WO2011003081A1

WO2011003081A1 - Method and system for converting electricity into alternative energy resources

Info

Publication number: WO2011003081A1
Application number: PCT/US2010/040944
Authority: WO
Inventors: Laurens Mets
Original assignee: The University Of Chicago
Priority date: 2009-07-02
Filing date: 2010-07-02
Publication date: 2011-01-06
Also published as: TWI500766B; BR112012000046B1; BR112012000046A2; US20210032582A1; HUE051809T2; DK2449084T3; US20220411733A1; EP3839860A1; EP2449084B1; EP2449084A4; TW201116628A; EP2449084A1

Abstract

A system to convert electric power into methane includes a biological reactor has at least a first chamber containing at least a cathode, a culture comprising methanogenic microorganisms, and water, and a second chamber containing at least an anode. The biological reactor has an operating state wherein the culture is maintained at a temperature above 50 °C. The system also includes a source of electricity coupled to the anode and the cathode, a supply of carbon dioxide coupled to the first chamber, and an outlet to receive methane from the first chamber.

Description

METHOD AND SYSTEM FOR CONVERTING

ELECTRICITY INTO ALTERNATIVE ENERGY RESOURCES

Background

[0001] This patent is directed to the conversion of electrical energy into alternative energy resources, such as fuels. In particular, the patent relates to conversion of carbon dioxide into methane and other energy resources using electrical energy, which conversion may also create or generate other products or byproducts, such as carbon credits or oxygen, for example.

[0002] The US annually consumes about 90 ExaJoules (EJ) of carbon-based fuels, 88% of its total energy consumption in 2008. The use of these fuels is supported by heavily capitalized processing, distribution and utilization industries.

[0003] The sustainability of these systems is questionable on two counts. First, the US imports 25% of the energy it uses, a proportion that is projected to increase substantially. Imported energy is obtained from sources that are under pressure to serve increasing demand from growing economies in other parts of the world. Second, more than 96% of the carbon- based fuels are obtained from fossil reserves, which are finite. Useful energy is obtained from carbon-based fuels by oxidizing reduced states of carbon to carbon dioxide. For fossil fuels, this process is basically open-loop, producing CO₂ with no compensating carbon reduction process to close the cycle. The consequent gradual accumulation of atmospheric CO₂ is beginning to cause changes in the global climate that threaten many aspects of our way of life. Therefore, a process that can close this carbon energy cycle for the total energy economy is needed.

[0004] An annual flux of 58,000 EJ of solar energy strikes US soil, making it our most abundant carbon-free energy resource - 500 times current consumption. Solar energy has the unique advantage of being a domestic resource not just in the US, but everywhere that people live. Its widespread use as a primary resource would secure energy independence throughout the world. Nevertheless, today solar energy is only a marginal component of the energy economy, providing less than 0.1% of marketed US energy consumption. Exploitation of solar energy is limited principally because it is intermittent and cannot be relied upon to provide the base-load energy that must be available whenever needed. What is lacking is a method for storing solar energy in a stable form that can be tapped whenever needed. Ideally, such a storage form should fit smoothly into the existing energy infrastructure so that it can be quickly deployed once developed.

[0005] There is a need in the energy industry for systems to convert one form of energy into another. In particular, there is a need for systems to convert electricity into a form of energy that can be stored inexpensively on industrial scales. Many sources of electricity generation cannot be adjusted to match changing demand. For example, coal power plants run most efficiently when maintained at a constant rate and cannot be adjusted as easily as natural gas (methane) fired power plants. Likewise, wind turbines generate electricity when the wind is blowing which may not necessarily happen when electricity demand is highest.

[0006] There is also a need to convert electricity into a form that can be transported long distances without significant losses. Many opportunities for wind farms, geothermal, hydroelectric or solar based power generation facilities are not located close to major population centers, but electric power losses over hundreds of miles add significant cost to such distant power facilities.

[0007] Methane is one of the most versatile forms of energy and can be stored easily. There already exists much infrastructure for transporting and distributing methane as well as infrastructure for converting methane into electricity and for powering vehicles. Methane also has the highest energy density per carbon atom of all fossil fuels, and therefore of all fossil fuels, methane releases the least carbon dioxide per unit energy when burned. Hence, systems for converting electricity into methane would be highly useful and valuable in all energy generation and utilization industries.

[0008] In principle, it would be possible to produce methane from electric power in a two-step process, such as outlined schematically in Fig. 1. The first step would use the electric power to make hydrogen gas from water in a standard water electrolysis system 50. In a second step, the hydrogen gas could then be pumped into a methanogenic reaction chamber 52 such as a highly specific biological reactor of methanogenic microbes. One such biological reactor is described in U.S. patent application 12/333,932 by Laurens Mets, which is incorporated in its entirety herein by reference.

Summary

[0009] According to an aspect of the present disclosure, a system to convert electric power into methane includes a biological reactor having at least a first chamber containing at least a cathode, a culture comprising methanogenic microorganisms, and water, and a second chamber containing at least an anode. The biological reactor has an operating state wherein the culture is maintained at a temperature above 50 ⁰C. The system also includes a source of electricity coupled to the anode and the cathode, a supply of carbon dioxide coupled to the first chamber, and an outlet to receive methane from the first chamber.

[0010] According to another aspect of the present disclosure, a method of converting electricity into methane includes supplying electricity to an anode and a cathode of biological reactor having at least a first chamber containing at least the cathode, a culture comprising methanogenic microorganisms, and water, and a second chamber containing at least the anode, the biological reactor having an operating state, wherein the culture is maintained at a temperature above 50 ⁰C. The method also includes supplying carbon dioxide to the first chamber, and collecting methane from the first chamber.

[0011] According to a further aspect of the present disclosure, a method of creating carbon credits includes supplying electricity to an anode and a cathode of biological reactor having at least a first chamber containing at least the cathode, a culture comprising methanogenic microorganisms, and water, and a second chamber containing at least the anode, the biological reactor having an operating state wherein the culture is maintained at a temperature about 50 ⁰C. The method also includes supplying carbon dioxide to the first chamber, and receiving carbon credits for the carbon dioxide converted in the biological reactor into methane.

Brief Description of the Drawings

[0012] It is believed that the disclosure will be more fully understood from the following description taken in conjunction with the accompanying drawings. Some of the figures may have been simplified by the omission of selected elements for the purpose of more clearly showing other elements. Such omissions of elements in some figures are not necessarily indicative of the presence or absence of particular elements in any of the exemplary embodiments, except as may be explicitly delineated in the corresponding written

description. None of the drawings is necessarily to scale.

[0013] Fig. 1 is a schematic view of a system for converting carbon dioxide into methane according to the prior art;

[0014] Fig. 2 is a schematic view of a system for converting carbon dioxide into methane according to the present disclosure;

[0015] Fig. 3 is a cross-sectional view of an embodiment of a biological reactor for converting carbon dioxide into methane; [0016] Fig. 4 is a cross-sectional view of another embodiment of a biological reactor for converting carbon dioxide into methane;

[0017] Fig. 5 is a cross-sectional view of yet another embodiment of a biological reactor for converting carbon dioxide into methane;

[0018] Fig. 6 is a cross-sectional view of a further embodiment of a biological reactor for converting carbon dioxide into methane;

[0019] Fig. 7 is a schematic view of an embodiment of a biological reactor with a plurality anodes and cathodes;

[0020] Fig. 8 is a cross-sectional view of the system of Fig. 7 taken along line 8-8;

[0021] Fig. 9 is a cross-sectional view of one of the plurality of biological reactors of

Fig. 8 taken along line 9-9;

[0022] Fig. 10 is a cross-sectional view of a variant biological reactor for use in the system of Fig. 7;

[0023] Fig. 11 is a schematic view of a series arrangement of biological reactors according to the present disclosure;

[0024] Fig. 12 is a schematic view of a parallel arrangement of biological reactors according to the present disclosure;

[0025] Fig. 13 is a schematic view of a stand-alone system according to the present disclosure;

[0026] Fig. 14 is a schematic view of an integrated system according to the present disclosure; and

[0027] Fig. 15 is a graph of methane production over time with varying voltage applied across the anode and cathode of a biological reactor according to Fig. 3.

Detailed Description of Various Embodiments

[0028] Although the following text sets forth a detailed description of numerous different embodiments of the invention, it should be understood that the legal scope of the invention is defined by the words of the claims set forth at the end of this patent. The detailed description is to be construed as exemplary only and does not describe every possible embodiment of the invention since describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims defining the invention. [0029] It should also be understood that, unless a term is expressly defined in this patent using the sentence "As used herein, the term ' ' is hereby defined to mean..." or a similar sentence, there is no intent to limit the meaning of that term, either expressly or by implication, beyond its plain or ordinary meaning, and such term should not be interpreted to be limited in scope based on any statement made in any section of this patent (other than the language of the claims). To the extent that any term recited in the claims at the end of this patent is referred to in this patent in a manner consistent with a single meaning, that is done for sake of clarity only so as to not confuse the reader, and it is not intended that such claim term be limited, by implication or otherwise, to that single meaning. Finally, unless a claim element is defined by reciting the word "means" and a function without the recital of any structure, it is not intended that the scope of any claim element be interpreted based on the application of 35 U. S. C. §112, sixth paragraph.

[0030] The present disclosure addresses the processing or conversion of carbon dioxide into methane using an electro-biological apparatus. The apparatus may be referred to herein as a biological reactor, bioreactor, processor, converter or generator. It will be recognized that this designation is not intended to limit the role that the converter may perform within a system including one or more converters.

[0031] For example, the apparatus provides a non-fossil carbon-based energy resource. In this regard, the apparatus is being used to generate an energy resource that may be substituted for fossil-based carbon fuels, to reduce reliance on fossil-based carbon fuels, for example. Additionally, the apparatus converts or processes carbon dioxide to generate this energy resource. In this regard, the apparatus removes carbon dioxide from the environment, which may be a beneficial activity in and of itself. Such removal of carbon dioxide from the environment may happen by removing carbon dioxide directly from the atmosphere or by utilizing carbon dioxide from another industrial process and thereby preventing such carbon dioxide from being released into the atmosphere or into a storage system or into another process. Further, the apparatus converts or processes carbon dioxide into methane using electricity to convert electricity into another energy resource when demand for electricity may be such that the electricity would otherwise be wasted or even sold at a loss to the electricity producer, for example. In this regard, the apparatus may be viewed as part of an energy storage system. In the operation of a power grid, or an individual power plant or other power source on the grid, or as part of a facility not associated with a power grid, or in the operation of a biological reactor, available power output may be used by one or more biological reactors to consume as an input carbon dioxide, water or electrical power and to produce methane or oxygen when business conditions are favorable to provide an incentive greater than for other use of such inputs. Such conditions may exist when certain regulatory policies, power purchase agreements, carbon credits, futures trading opportunities, storage capacity, electrical demand, taxes, tax credits or abatements, contracts, customer preferences, transmission capacity, pricing conditions, or other market incentives can provide sufficient value for operation of the biological reactor to produce methane or oxygen or to consume carbon dioxide, water or electrical power. In addition to the above and other uses, the apparatus converts electrical energy or power into methane which may be transmitted via natural gas transmission pipes which on a per unit energy basis are less expensive than electrical transmission lines and in some locales the electrical transmission lines may not have as much spare transmission capacity as the natural gas transmission lines. In this regard, the apparatus may be viewed as part of an energy transmission system. All of these roles may be performed by an apparatus according to the present disclosure.

[0032] As illustrated in Fig. 2, the biological reactor according to the present disclosure may include a container that is divided into at least a first chamber and a second chamber. At least one cathode is disposed in the first chamber, and at least one anode is disposed in the second chamber. The first chamber may have inlets that are connected to a source of carbon dioxide gas and a source of water, and an outlet that is connected, for example, to a storage device used to store methane produced in the first chamber. The first and second chambers are separated by a divider that is permeable to ions (protons) to permit them to move from the second chamber to the first chamber. This membrane also may be impermeable to the gaseous products and by-products of the conversion process to limit or prevent them from moving between the first chamber and the second chamber.

I. Description of System and Biological Reactor

[0033] Methanogenic microorganisms may be cultured, for example, in shake or stirred tank bioreactors, hollow fiber bioreactors, or fluidized bed bioreactors, and operated in a batch, fed batch, continuous, semi-continuous, or perfusion mode. In batch mode (single batch), an initial amount of medium containing nutrients necessary for growth is added to the biological reactor, and the biological reactor is operated until the number of viable cells rises to a steady-state maximum, or stationary condition. In fed-batch mode, concentrated media or selected amounts of single nutrients are added at fixed intervals to the culture. Methanogenic microorganisms can survive for years under fed batch conditions, provided that any waste products are effectively minimized or removed to prevent loss of efficiency of methane production over time. Any inhibitory waste products may be removed by continuous perfusion production processes, well known in the art. Perfusion processes may involve simple dilution by continuous feeding of fresh medium into the culture, while the same volume is continuously withdrawn from the reactor. Perfusion processes may also involve continuous, selective removal of medium by centrifugation while cells are retained in the culture or by selective removal of toxic components by dialysis, adsorption,

electrophoresis, or other methods. Continuously perfused cultures may be maintained for weeks, months or years.

[0034] Fig. 3 illustrates a first embodiment of a system 100 that may be used, for example, to convert electric power into methane. The system 100 includes a biological reactor 102 having at least a first chamber 104 and a second chamber 106. The first chamber 104 may contain at least a cathode 108, a culture comprising living methanogenic microorganisms, and water. In particular, the culture may comprise autotrophic and/or hydrogenotrophic methanogenic archaea, and the water may be part of an aqueous electrolytic medium compatible with the living microorganisms. The second chamber may contain at least an anode 110.

[0035] The biological reactor 102 may also include a selectively permeable barrier 112, which may be a proton permeable barrier, separating the anode 110 from the cathode 108. The barrier 112 may be at least gas semipermeable (e.g., certain gases may pass through, while others are limited), although according to certain embodiments, the barrier 112 is impermeable to gases. According to certain embodiments, the barrier 112 may prevent gases produced on each side of the barrier from mixing.

[0036] According to certain embodiments, the barrier 112 may be a solid polymer electrolyte membrane (PEM), such as is available under tradename Nafion from E. I. du Pont de Nemours and Company. For optimum energy conversion in the reactor according to certain embodiments, it is believed that the permeability of the barrier to hydronium ions should preferably be a minimum of two orders of magnitude greater on a molar basis than permeability of the barrier to oxygen under conditions of operation of the reactor. Other suitable PEM membranes that meet these criteria, such as sulfonated polyarylene block copolymers (see, e.g., Bae, B., K Miyatake, and M. Watanabe. Macromolecules 43:2684-2691 (2010), which is incorporated by reference herein in its entirety) and PTFE- supported Nafion (see, e.g., G.-B. Jung, et al, J Fuel Cell Technol 4:248-255(2007), which is incorporated by reference herein in its entirety), are under active development in numerous laboratories. Suitable commercial PEM membranes, in addition to Nafion, include Gore-Select

(PRIMEA), Flemion (Asahi), 3M Fluoropolymer ionomer, SPEEK (Polyfuel), Kynar blended membrane (Arkema), Fumapem (FuMA-Tech), and Solupor (Lydall).

[0037] In the biological reactor 102, water acts as a primary net electron donor for the methanogenic microorganisms (e.g, methanogenic archaea) in the biological reactor.

Accordingly, it is also believed that the barrier 112 should be permeable for hydronium ions (H₃O⁺) (i.e., enable hydronium ions to cross the barrier 112 from the anode 110 to the cathode 108 and complete the electrical circuit).

[0038] The cathode 108 may be of a high surface to volume electrically conductive material. For example, the cathode 108 may be made of a porous electrically conductive material. In particular, the cathode 108 may be made from a reticulated vitreous carbon foam according to certain embodiments. As explained in greater detail below, other materials may be used. According to certain embodiments, the pores of the cathode may be large enough (e.g., greater than 1-2 micrometers in minimum dimension) to accommodate living methanogenic microorganisms within the pores. The electrical conductivity of the cathode matrix is preferably at least two orders of magnitude greater than the ion conductivity of the aqueous electrolytic medium contained within its pores.

[0039] It will be recognized that the role of the cathode 108 is to supply electrons to the microorganisms while minimizing side-reactions and minimizing energy loss. Additionally, it is advantageous for the cathode to be inexpensive. At the present time, it is believed that certain materials may be more or less suitable for inclusion in the reactor.

[0040] For instance, platinum cathodes may be less suitable for inclusion in the reactor. In this regard, the platinum provides a surface highly active for catalyzing hydrogen gas production from the combination of protons or hydronium ions with electrons provided by the cathode. The activity of platinum cathode catalysts for hydrogen formation in aqueous solutions is so high that the hydrogen concentration in the vicinity of the catalyst quickly rises above its solubility limit and hydrogen gas bubbles emerge. Despite the fact that the methanogenic microorganisms are evolved to consume hydrogen in the process of methane formation, hydrogen in bubbles re-dissolves only slowly in the medium and is largely unavailable to the microorganisms. Consequently, much of the energy consumed in hydrogen formation at a platinum catalyst does not contribute to methane formation. Additionally, the binding energy of hydrogen is higher than the binding energy per bond of methane. This difference results in an energetic loss when hydrogen gas is produced as an intermediate step.

[0041] On the other hand, a solid carbon cathode is an example of an inexpensive, electrically conductive material that has low activity for hydrogen formation and that can provide electrons to microorganisms. However, it will be recognized that electron transfer between microorganisms and an external electron source or sink, such as an electrode, requires some level of proximity between the microorganisms and the electrode and the total rate of electron transfer is related to the area of electrode in close contact with

microorganisms. Since a porous electrode that allows the microorganisms to enter the pores has a much larger surface area in proximity to the microorganisms than a planar electrode of equivalent dimensions, the porous electrode is expected to provide superior volumetric current density.

[0042] A suitable porous cathode material may be provided by reticulated vitreous carbon foam, as demonstrated in Example 1. It is inexpensive and conductive. Its porous structure provides for electrical connections to a large number of the microorganisms allowing for a high volumetric productivity. Additionally, the vitreous nature of the carbon provides low activity for hydrogen production, which increases both energetic and Faradaic efficiency. It will also be recognized that vitreous carbon is also very resistant to corrosion.

[0043] Other suitable porous electrode materials may include, but are not limited to graphite foam (see, e.g., US Patent 6033506, which is incorporated by reference herein in its entirety), woven carbon and graphite materials, carbon, graphite or carbon nanotube impregnated paper (see, e.g., Hu, L., et al. Proc Nat Acad Sci USA 106: 21490-4 (2009), which is incorporated by reference herein in its entirety), and metal foams, or woven or non- woven mesh comprised of materials, such as titanium, that are non-reactive under the conditions of the reaction and that present a high surface to volume ratio.

[0044] Further enhancement of electron transfer between the cathode and the

microorganisms may be achieved with conductive fibers. Suitable conductive fibers may consist of conductive pili generated by the microorganisms as described in more detail below. Alternatively or additionally, nanowires, such as carbon nanotubes (Iijima, S. Nature 354:56 (1991), which is incorporated by reference herein in its entirety), may be attached directly to the cathode. Wang, J. et al, J. Am. Chem. Soc. 125:2408-2409 (2003) and references therein, all of which are incorporated by reference herein in their entirety, provide techniques for modifying glassy carbon electrodes with carbon nanotubes. Additionally, conductive organic polymers may be used for this purpose (see, e.g., Jiang, P. Angewandte Chemie 43:4471- 4475 (2004), which is incorporated by reference herein in its entirety). Non-conductive materials that bind the microorganisms to the surface of the electrode may also enhance electron transfer. Suitable non-conductive binders include but are not limited to poly-cationic polymers such as poly-lysine or poly(beta -aminosulfonamides). The living methanogenic microorganisms may also produce biological materials, such as those that support biofilm formation, that effectively bind them to the surface of the electrode.

[0045] The anode 110 may comprise a Pt-carbon catalytic layer or other materials known to provide low overpotential for the oxidation of water to oxygen.

[0046] As illustrated in Fig. 3, a source of electricity 120 is coupled to the anode 110 and the cathode 108. As mentioned above, the source 120 may be generated from carbon-free, renewable sources. In particular, the source 120 may be generated from carbon-free, renewable sources such as solar sources (e.g., photovoltaic cell arrays) and wind sources (e.g., wind turbines). However, according to other embodiments, the source 120 may be a coal power plant, a fuel cell, a nuclear power plant. According to still further embodiments, the source 120 may be a connector to an electrical transmission grid. Further details are provided below.

[0047] Based upon dynamic computational models of porous electrodes containing aqueous electrolyte, the optimal conductivity of the cathode electrolyte is believed to be preferably in the range of 0.01 to 0.25 S/cm or higher in the operating state of the reactor. Higher conductivity of the electrolyte may reduce ohmic losses in the reactor and hence may increase energy conversion efficiency. Computational models further suggest that the optimal thickness of the porous cathode (perpendicular to the planes of the reactor layers) may be between 0.2 cm and 0.01 cm, or less. Thinner cathode layers may have lower ohmic resistance under a given set of operating conditions and hence may have an increased energy conversion efficiency.

[0048] The biological reactor 102 may operate at an electrical current density above 6 mA/cm . For example, the biological reactor 102 may operate at an electrical current density of between 6 and 10 mA/cm . According to certain embodiments, the biological reactor 102 may operate at electrical current densities at least one order of magnitude higher (e.g., 60-100 mA/cm ). The current may be supplied as direct current, or may be supplied as pulsed current such as from rectified alternating current. The frequency of such pulsed current is not constrained by the properties of the reactor. The frequency of the pulsed current may be variable, such as that generated by variable speed turbines, for example wind turbines lacking constant-speed gearing

[0049] The living methanogenic microorganisms (e.g., autotrophic and/or

hydrogenotrophic methanogenic archaea) may be impregnated into the cathode 108. While various embodiments and variants of the microorganisms are described in greater detail in the following section, it is noted that the microorganisms may be a strain of archaea adapted to nearly stationary growth conditions according to certain embodiments of the present disclosure. In addition, according to certain embodiments of the present disclosure, the microorganisms may be Archaea of the subkingdom Euryarchaeota, in particular, the microorganisms may consist essentially of Methanothermobacter thermautotrophicus.

[0050] As explained in greater detail below, the biological reactor 102 may have an operating state wherein the culture is maintained at a temperature above 50° C, although certain embodiments may have an operating state in the range of between approximately 60° C and 100° C. The biological reactor 102 may also have a dormant state wherein electricity and/or carbon dioxide is not supplied to the reactor 102. According to such a dormant state, the production of methane may be significantly reduced relative to the operating state, such that the production may be several orders of magnitude less than the operating state, and likewise the requirement for input electrical power and for input carbon dioxide may be several orders of magnitude less than the operating state. According to certain embodiments of the present disclosure, the biological reactor 102 may change between the operating state and the dormant state or between dormant state and operating state without addition of microorganisms to the reactor 102. Additionally, according to certain embodiments, the reactor 102 may change between dormant and operating state rapidly, and the temperature of the reactor 102 may be maintained during the dormant state to facilitate the rapid change.

[0051] The biological reactor 102 may have an inlet 130 connected to the first chamber for receiving gaseous carbon dioxide. The inlet 130 may be coupled to a supply of carbon dioxide 132 to couple the supply of carbon dioxide to the first chamber 104. The biological reactor 102 may also have an outlet 134 to receive methane from the first chamber.

[0052] The biological reactor 102 may also have an outlet 136 connected to the second chamber 106 for receiving byproducts. For example, gaseous oxygen may be generated in the second chamber 106 as a byproduct of the production of methane in the first chamber 104. According to certain embodiments, oxygen may be the only gaseous byproduct of the biological reactor 102. In either event, the gaseous oxygen may be received by the outlet 134 connected to the second chamber 106.

[0053] In keeping with the disclosure of Fig. 3, a method of the present disclosure may include supplying electricity to the anode 110 and the cathode 108 of the biological reactor 102 having at least the first chamber 104 containing at least the cathode 108, a culture comprising living methanogenic microorganisms (e.g., autotrophic and/or hydrogenotrophic methanogenic archaea), and water (e.g., as part of an aqueous electrolytic medium compatible with the living microorganisms), and the second chamber 106 containing at least the anode 110, wherein the culture is maintained at a temperature above 50 ⁰C. Further, the method may include generating electricity from carbon-free, renewable sources, such as from solar and wind sources, as noted above. According to certain embodiments, electricity may be supplied during a non-peak demand period. Further details are provided in section III, below.

[0054] The method may also include supplying carbon dioxide to the first chamber 104. As noted above, the method may include recycling carbon dioxide from at least a

concentrated industrial source or atmospheric carbon dioxide, which carbon dioxide is supplied to the first chamber 104.

[0055] The method may further include collecting methane from the first chamber 104. The method may further include storing and transporting the methane. The method may also include collecting other gaseous products or byproducts of the biological reactor; for example, the method may include collecting oxygen from the second chamber 106.

[0056] It will be recognized that while the system of Fig. 3 may be viewed as operating to convert electricity into methane, it is also possible to view the system of Fig. 3 as operating to create or earn carbon credits, as an alternative to carbon sequestration for example.

According to such a method, the method would include supplying electricity to the anode 110 and the cathode 108 of biological reactor 102 having at least the first chamber 104 containing at least the cathode 108, methanogenic microorganisms (e.g., methanogenic archaea), and water (e.g., as part of an aqueous electrolytic medium compatible with the living

microorganisms), and a second chamber containing at least the anode, wherein the culture is maintained at a temperature above 50 ⁰C. The method would also include supplying carbon dioxide to the first chamber 104. Finally, the method would include receiving carbon credits for the carbon dioxide converted in the biological reactor 102 into methane. According to such a method, the carbon dioxide may be recycled from a concentrated industrial source. [0057] It will be recognized that the system 100 is only one such embodiment of a system according to the present disclosure. Additional embodiments and variants of the system 100 are illustrated in Figs. 4-10, and will be described in the following section. While these embodiments are generally shown in cross-section, assuming a generally cylindrical shape for the reactor and disc-like shapes for the anode and cathode, which may be arranged parallel to one another as illustrated, it will be appreciated that other geometries may be used instead.

[0058] Fig. 4 illustrates a system 200 that includes a biological reactor 202, a source of electricity 204 and a source of carbon dioxide 206. As illustrated, the source of electricity 204 and the source of carbon dioxide 206 are both coupled to the biological reactor 202. The biological reactor 202 uses a circulating liquid/gas media, as explained in greater detail below.

[0059] The biological reactor 202 includes a housing 210 that defines, in part, first and second chambers 212, 214. The reactor 202 also includes a cathode 216 disposed in the first chamber 212, and an anode 218 disposed in the second chamber 214. The first and second chambers 212, 214 are separated by proton permeable, gas impermeable barrier 220, the barrier 220 having surfaces 222, 224 which also define in part the first and second chambers 212, 214.

[0060] The biological reactor 202 also includes current collectors 230, 232, one each for the cathode 216 and the anode 218. The current collector 230 for the cathode 216 may be made as a solid disc of material, so as to maintain a sealed condition within the chamber 212 between an inlet 234 for the carbon dioxide and an outlet 236 for the methane (and potentially byproducts). The inlet 234 and the outlet 236 may be defined in the housing 210. The current collector 232 for the anode 218 may also define a porous gas diffusion layer, on which the anode catalyst layer is disposed. It will be recognized that a porous gas diffusion layer should be provided so as to permit gaseous byproducts to exit the second chamber 214, because the barrier 220 prevents their exit through the outlet 236 via the first chamber 212.

[0061] In keeping with the disclosure above, the cathode 216 is made of a porous material, such as a reticulated carbon foam. The cathode 216 is impregnated with the methanogenic microorganisms and with the aqueous electrolytic medium. The methanogenic microorganisms (e.g., archaea) are thus in a passage 238 formed between the barrier 220 and the current collector 230 between the inlet 234 and the outlet 236. [0062] In operation, carbon dioxide is dissolved into the aqueous electrolytic medium and is circulated through the cathode 216. The methanogenic microorganisms may reside within the circulating electrolytic medium or may be bound to the porous cathode 216. In the presence of an electric current, the methanogenic microorganisms process the carbon dioxide to generate methane. The methane is carried by the electrolytic medium out of the reactor 202 via the outlet 236. According to such an embodiment, post-processing equipment, such as a liquid/gas separator, may be connected to the outlet to extract the methane from the solution.

[0063] Fig. 5 illustrates a system 250 including a reactor 252 that is a variant of that illustrated in Fig. 4. Similar to the reactor 202, the reactor 252 includes a housing 260 that defines, in part, first and second chambers 262, 264. The reactor 252 also includes a cathode 266 disposed in the first chamber 262, and an anode 268 disposed in the second chamber 264. The first and second chambers 262, 264 are separated by proton permeable, gas impermeable barrier 270, the barrier 270 having surfaces 272, 274 that also define in part the first and second chambers 262, 264.

[0064] Unlike the embodiment illustrated in Fig. 4, the embodiment illustrated in Fig. 5 also includes a porous, proton conducting gas diffusion layer 280. The gas diffusion layer 280 is disposed between the cathode 266 and the barrier 270. Using this gas diffusion layer 280, gaseous carbon dioxide may enter the first chamber 212 through the gas diffusion layer 280 and then diffuse into the cathode 266, while gaseous methane produced by the microorganisms may diffuse from the cathode 266 into the layer 280 and then out of the first chamber 212. Proton-conducting gas diffusion layers suitable for use as layer 280 may be produced by coating porous materials with proton-conducting ionomer, by incorporating ionomer directly into the porous matrix, or by chemical derivitization of porous matrix materials with sulfate, phosphate, or other groups that promote proton-conduction, for example.

[0065] It will thus be recognized that the carbon dioxide and the methane are not carried by a circulating liquid media according to the embodiment of Fig. 5. Instead, the culture and the media are contained in the first chamber 262, while only the gaseous carbon dioxide and the methane circulate between inlet and outlet. Such an embodiment may present certain advantages relative to the reactor 202 of Fig. 4, in that the handling of the methane postprocessing or generation may be simplified. Further, the absence of a circulating liquid media in the reactor 202 may simplify the serial connection between multiple reactors, as illustrated in Fig. 11. However, while the circulating media in the embodiment of Fig. 4 provided any water required by the culture, it may be necessary to couple equipment to the reactor to provide water vapor to the culture, in addition to the gaseous carbon dioxide. The electrolytic medium and microorganisms may be retained within the pores of the cathode 266 by surface tension or alternatively by including materials within the electrolyte that increase its viscosity or form a gel.

[0066] Fig. 6 illustrates a system 300 including a reactor 302 that is a variant of that illustrated in Fig. 5. Similar to the reactors 202 and 252, the reactor 302 includes a housing 310 that defines, in part, first and second chambers 312, 314. The reactor 302 also includes a cathode 316 disposed in the first chamber 312, and an anode 318 disposed in the second chamber 314. The first and second chambers 312, 314 are separated by proton permeable, gas impermeable barrier 320, the barrier 320 having surfaces 322, 324 that also define in part the first and second chambers 312, 314.

[0067] Moreover, similar to the embodiment illustrated in Fig. 5, the embodiment illustrated in Fig. 6 also includes a porous, proton conducting gas diffusion layer 330.

However, the gas diffusion layer 330 is not disposed between the cathode 316 and the barrier 320, but instead is disposed between the cathode 316 and the current collector 332. In this arrangement, the gas diffusion layer 330 is current-conducting rather than proton-conduction like the gas diffusion layer 280 in reactor 252. Current would pass through the layer 330 into the cathode 316. As in the reactor 252, the carbon dioxide still would enter the first chamber 312 passes through the gas diffusion layer 330 and diffuse into the cathode 316, while methane produced by the microorganisms would diffuse from the cathode 316 through the layer 330.

[0068] As a result, the embodiment of Fig. 6 illustrates a reactor wherein the gaseous carbon dioxide enters the cathode from a side or along a path opposite that of the protons. By comparison, the embodiment of Fig. 5 illustrates a reactor wherein the gaseous carbon dioxide and the protons enter the cathode from the same side or along a similar path. The counter-diffusion of the embodiment of Fig. 6 may provide slower production than that of Fig. 5, but may provide acceptable production levels. As to the material used for the barrier 320 according to such an embodiment, it is believed that a porous carbon foam impregnated with Nafion particles may be suitable.

[0069] Figs. 7-10 illustrate a system 400 including a biological reactor 402 that highlights several aspects of the present disclosure over and above those illustrated in Figs. 2- 6. In particular, while the general nature of the reactor (with first and second chambers, anode, cathode, barrier, microorganisms, and aqueous electrolytic medium) has much in common with the systems illustrated in Figs. 2-6, the reactor 402 illustrates new geometries, as well as a reactor in which a plurality of anodes and a plurality of cathodes are present.

[0070] In particular, as illustrated in Fig. 7, the reactor 402 includes a number of tubular reactor subunits 404 that may be arranged in a matrix format. It will be recognized that the particular arrangement of the subunits 404 utilizes an offset relative to the arrangement of adjacent rows of subunits 404, so as to increase the number of subunits 404 within a volume. It will also be recognized that adjacent rows of subunits 404 may be aligned with each other instead. It will also be recognized that while four rows of five subunits 404 each and four rows of four subunits 404 each have been illustrated, this should not be taken as limiting the reactor 402 thereby.

[0071] Fig. 8 illustrates a plurality of subunits in cross-section, so as to appreciate the similarities and differences with the systems illustrated in Figs. 2-6 above. While it need not be the case for all embodiments, each of the subunits 404 illustrated in Fig. 8 is identical, such that discussion of any one of the subunits 404 would be inclusive of remarks that may be made relative to the other subunits 404 as well.

[0072] As seen in Fig. 8, the reactor 402 includes a housing 410, in which the subunits 404 are disposed. It will be recognized that the housing 410 is sealed against leakage of products and byproducts as explained in greater detail below. Disposed at one end of the housing 410 is a common current collector 412 that is connected to a generally tubular cathode 414 of each of the subunits 404. In a similar fashion, the reactor 402 includes a porous gas diffusion layer/current collector 416 that is connected to a generally tubular anode 418 of each subunit 404. Disposed between the cathode 414 and the anode 418 is a generally tubular proton-permeable, gas impermeable barrier 420, as is discussed in greater detail above. This arrangement is also illustrated in Fig. 9.

[0073] According to this embodiment, the carbon dioxide enters the reactor 402 via an inlet 430 and moves along a passage 432. The carbon dioxide then passes along the porous cathode 414, which is impregnated with methanogenic microorganisms and aqueous electrolytic medium. The methane produced in the cathode 414 then is collected in a space 434 that is connected to the outlet 436. [0074] Fig. 10 illustrates a variant to the subunit 404 illustrated relative to the system 400 in Figs. 7 and 8. Given the similarities between the subunit 404 and its variant, the common structures will be designated with a prime.

[0075] As illustrated in Fig. 10, the subunit 404' includes a tubular cathode 414', a tubular anode 418' and a tubular barrier 420'. As in the subunit 404, the tubular cathode 414' is disposed centrally of the subunit 404', with the anode 418' disposed radially outward of the cathode 416' and the barrier 420' disposed therebetween. However, similar to the variants described in Fig. 5, the subunit 404' includes a porous, proton-conducting gas diffusion layer 440. This layer 440 may be in communication with the passage 432 and the space 434 in a reactor 402, instead of the cathode 414'. As such, carbon dioxide would pass from the inlet 430 through the layer 440 to the cathode 414', while methane would pass from the cathode 414' through the layer 440 to the outlet 436. An arrangement similar to Fig. 10, but with an electrically conductive gas diffusion layer arranged as in Fig 6 between the cathode 414' and the current collector 412' is also possible.

[0076] Figs. 11 and 12 illustrate two different power management options that may be used with any of the reactors described above. In this regard, it will be recognized that each of the systems 450, 452 illustrated in Figs. 11 and 12 may include a plurality of individual reactors 454, 456.

[0077] In Fig. 11, the individual reactors 454 are connected in series to match a fixed or constant voltage. The system 450 accommodates a variable current by providing a plurality of switches 458 to permit additional series chains of reactors 454 to be switched into the circuit to match variable current. In Fig. 12, the individual reactors 456 are connected in parallel to match a fixed or constant current. The system 452 accommodates a variable voltage by providing pairs of switches 460 to permit additional parallel planes of reactors 456 to be switched into the circuit to match variable voltage. It will be recognized that it may also be possible to address variable current and variable voltage applications with addressable switching so as to build dynamic parallel reactor planes and to adjust the lengths of series chains as needed.

II. Cultures comprising methanogenic microorganisms

Cultures

[0078] With regard to the present invention, the reactor (also referred to herein as the electromethanogenic reactor, the electrobiological methanogenesis reactor, the biological reactor, the bioreactor, etc.) comprises a culture comprising methanogenic microorganisms (a term used interchangeably with "methanogens"). The term "culture" as used herein refers to a population of live microorganisms in or on culture medium. When part of the reactor, the culture medium also serves as the electrolytic medium facilitating electrical conduction within the reactor.

Monocultures, Substantially Pure Cultures

[0079] In some embodiments, the culture is a monoculture and/or is a substantially-pure culture. As used herein the term "monoculture" refers to a population of microorganisms derived or descended from a single species (which may encompass multiple strains) or a single strain of microorganism. The monoculture in some aspects is "pure," i.e., nearly homogeneous, except for (a) naturally-occurring mutations that may occur in progeny and (b) natural contamination by non-methanogenic microorganisms resulting from exposure to non- sterile conditions. Organisms in monocultures can be grown, selected, adapted, manipulated, modified, mutated, or transformed, e.g. by selection or adaptation under specific conditions, irradiation, or recombinant DNA techniques, without losing their monoculture nature.

[0080] As used herein, a "substantially-pure culture" refers to a culture that substantially lacks microorganisms other than the desired species or strain(s) of microorganism. In other words, a substantially-pure culture of a strain of microorganism is substantially free of other contaminants, which can include microbial contaminants (e.g., organisms of different species or strain). In some embodiments, the substantially-pure culture is a culture in which greater than or about 70%, greater than or about 75%, greater than or about 80%, greater than or about 85%, greater than or about 90%, greater than or about 91%, greater than or about 92%, greater than or about 93%, greater than or about 94%, greater than or about 95%, greater than or about 96%, greater than or about 97%, greater than or about 98%, greater than or about 99% of the total population of the microorganisms of the culture is a single, species or strain of methanogenic microorganism. By way of example, in some embodiments, the

substantially-pure culture is a culture in which greater than 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more of the total population of

microorganisms of the culture is a single methanogenic microorganism species, e.g.,

Methanothermobacter thermautotrophicus .

[0081] When initially set up, the biological reactor is inoculated with a pure or substantially pure monoculture. As the biological reactor is exposed to non-sterile conditions during operation, the biological reactor may be contaminated by other non-methanogenic microorganisms in the environment without significant impact on operating efficiency over a period of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 months, or 1.5 or 2 years.

Mixed Cultures

[0082] In other embodiments, the culture comprises a plurality of (e.g., a mixture or combination of two or more) different species of methanogenic microorganisms. In some aspects, the culture comprises two, three, four, five, six, seven, eight, nine, ten, or more different species of methanogenic microorganisms. In some aspects, the culture comprises a plurality of different species of methanogenic microorganisms, but the culture is substantially free of any non-methanogenic microorganism.

[0083] In yet other embodiments, the culture comprises a plurality of microorganisms of different species, in which at least one is a methanogenic microorganism. In some aspects of this embodiment, the culture comprises at least one species of methanogenic microorganism and further comprises at least one selected non-methanogenic microorganism. In some aspects, the culture comprises two or more different species of methanogens, and, optionally comprises at least one selected non-methanogenic microorganism.

[0084] Suitable cultures of mixtures of two or more microbes are also readily isolated from the specified environmental sources (Bryant et al. Archiv Microbiol 59:20-31 (1967) "Methanobacillus omelianskii, a symbiotic association of two species of bacteria.", which is incorporated by reference herein in its entirety). Suitable mixtures may be consortia in which cells of two or more species are physically associated or they may be syntrophic mixtures in which two or more species cooperate metabolically without physical association. Also, suitable mixtures may be consortia in which cells of two or more species are physically associated or they may be syntrophic mixtures in which two or more species cooperate metabolically with physical association. Mixed cultures may have useful properties beyond those available from pure cultures of known hydrogenotrophic methanogens. These properties may include, for instance, resistance to contaminants in the gas feed stream, such as oxygen, ethanol, or other trace components, or aggregated growth, which may increase the culture density and volumetric gas processing capacity of the culture. Another contaminant in the gas feed stream may be carbon monoxide.

[0085] Suitable cultures of mixed organisms may also be obtained by combining cultures isolated from two or more sources. One or more of the species in a suitable mixed culture should be an Archaeal methanogen. Any non-Archael species may be bacterial or eukaryotic. [0086] Mixed cultures have been described in the art. See, for example, Cheng et al., U.S. 2009/0317882, and Zeikus US 2007/7250288, each of which is incorporated by reference in its entirety.

Reactor States and Growth Phases

[0087] As described herein, the reactor may be in a dormant (e.g., off) state or in an operating (e.g., on) state with regard to the production of methane, and, consequently, the reactor may be turned "on" or "off as desired in accordance with the need or desire for methane production. In some embodiments, the methanogenic microorganisms of the culture are in a state which accords with the state of the reactor. Therefore, in some embodiments, the methanogenic microorganisms are in a dormant state in which the methanogenic microorganisms are not producing methane (e.g., not producing methane at a detectable level). In alternative embodiments, the methanogenic microorganisms are in an operating state in which the methanogenic microorganisms are producing methane (e.g., producing methane at a detectable level).

[0088] When the methanogenic microorganisms are in the operating state, the methanogenic microorganisms may be in one of a variety of growth phases, which differ with regard to the growth rate of the microorganisms (which can be expressed, e.g., as doubling time of microorganism number or cell mass). The phases of growth typically observed include a lag phase, an active growth phase (also known as exponential or logarithmic phase when microorganisms multiply rapidly), a stationary phase, and a death phase (exponential or logarithmic decline in cell numbers). In some aspects, the methanogenic microorganisms of the biological reactor are in a lag phase, an active growth phase, a stationary phase, or a nearly stationary phase .

Active growth phase

[0089] In some embodiments, the methanogenic microorganisms are in an active growth phase in which the methanogenic microorganisms are actively multiplying at a rapid rate.

[0090] In some aspects, during operation of the biological reactor, the doubling time of the microorganisms may be rapid or similar to that observed during the growth phase in its natural environment or in a nutrient-rich environment. For example, the doubling time of many methanogenic microorganisms in the active growth phase is about 15 minutes, about 20 minutes, about 30 minutes, about 45 minutes, about 60 minutes, about 75 minutes, about 80 minutes, about 90 minutes, or about 2 hours.

Stationary growth phase, nearly stationary growth phase [0091] Stationary phase represents a growth phase in which, after the logarithmic or active growth phase, the rate of cell division and the rate of cell death are in equilibrium or near equilibrium, and thus a relatively constant concentration of microorganisms is maintained in the reactor. (See, Eugene W. Nester, Denise G. Anderson, C. Evans Roberts Jr., Nancy N. Pearsall, Martha T. Nester; Microbiology: A Human Perspective, 2004, Fourth Edition, Chapter 4, which is incorporated by reference herein in its entirety).

[0092] In other embodiments, the methanogenic microorganisms are in an stationary growth phase or nearly stationary growth phase in which the methanogenic microorganisms are not rapidly growing or have a substantially reduced growth rate. In some aspects, the doubling time of the methanogenic microorganisms is about 1 week or greater, including about 2, 3, 4 weeks or greater, or 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 months or greater.

[0093] In some embodiments, the reactor comprises a culture comprising methanogenic microorganisms, which microorganisms are initially in an active growth phase, and subsequently in a stationary or nearly stationary phase. In some embodiments, the reactor comprises a culture comprising methanogenic microorganisms which cycle between a dormant and an operating state.

Methanogenesis

[0094] As used herein, the term "methanogenic" refers to microorganisms that produce methane as a metabolic byproduct. In some embodiments, the reactor (also referenced herein interchangeably as electromethanogenic reactor, biological reactor or bioreactor, etc.) comprises a culture comprising hydrogenotrophic methanogenic microorganisms. As used herein, the term "hydrogenotrophic" refers to a microorganism capable of converting hydrogen to another compound as part of its metabolism. Hydrogenotrophic methanogenic microorganisms are capable of utilizing hydrogen in the production of methane. In some embodiments, the reactor comprises a culture comprising autotrophic methanogenic microorganisms. As used herein, the term "autotrophic" refers to a microorganism capable of using carbon dioxide and a source of reducing power to provide all carbon and energy necessary for growth and maintenance of the cell (e.g., microorganism). Suitable sources of reducing power may include but are not limited to hydrogen, hydrogen sulfide, sulfur, formic acid, carbon monoxide, reduced metals, sugars (e.g., glucose, fructose), acetate, photons, or cathodic electrodes or a combination thereof. In some aspects, the methanogenic

microorganisms produce methane from carbon dioxide, electricity, and water, a process referred to as electrobiological methanogenesis. [0095] The methanogenic microorganisms produce substantial amounts of methane in the operating state, as described herein. In some aspects, the methanogenic microorganisms produce methane in an active growth phase or stationary growth phase or nearly stationary growth phase.

[0096] The efficiency of methane production per molecule of carbon dioxide (CO₂) by the methanogenic microorganisms may be any efficiency suitable for the purposes herein. It has been reported that naturally-occurring methanogenic microorganisms in the active growth phase produce methane at a ratio of about 8 CO₂ molecules converted to methane per molecule of CO₂ converted to cellular material, ranging up to a ratio of about 20 CO₂ molecules converted to methane per molecule of CO₂ converted to cellular material. In some embodiments, the methanogenic microorganisms of the biological reactor of the present invention demonstrate an increased efficiency, particularly when adapted to stationary phase growth conditions. Accordingly, in some aspects, the ratio of the number of CO₂ molecules converted to methane to the number of CO₂ molecules converted to cellular material is higher than the ratio of naturally-occurring methanogenic microorganisms in the active growth phase. In exemplary embodiments, the ratio of the number of CO₂ molecules converted to methane to the number of CO₂ molecules converted to cellular material is N:l, wherein N is a number greater than 20, e.g. about 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or higher. In some aspects, N is less than 500, less than 400, less than 300, or less than 200. In some aspects, N ranges from about 40 to about 150.

Archaea

Naturally-Occurring Archaea

[0097] In some embodiments, the methanogenic microorganisms, e.g., the autotrophic methanogenic microorganisms, are archaea. The term "Archaea" refers to a categorization of organisms of the division Mendosicutes, typically found in unusual environments and distinguished from the rest of the prokaryotes by several criteria, including ether- linked membrane lipids and lack of muramic acid in cell walls. On the basis of ssrRNA analysis, the Archaea consist of two phylogenetically-distinct groups: Crenarchaeota and

Euryarchaeota. On the basis of their physiology, the Archaea can be organized into three partially overlapping groupings: methanogens (prokaryotes that produce methane); extreme halophiles (prokaryotes that live at very high concentrations of salt (NaCl); and extreme (hyper) thermophiles (prokaryotes that live at very high temperatures - e.g., 50-122⁰C). Besides the unifying archaeal features that distinguish them from bacteria (i.e., no murein in cell wall, ether-linked membrane lipids, etc.), these prokaryotes exhibit unique structural or biochemical attributes which adapt them to their particular habitats. The Crenarchaeota consist mainly of hyperthermophilic sulfur-dependent prokaryotes and the Euryarchaeota contain the methanogens and extreme halophiles.

[0098] Methanogens (or methanobacteria) suitable for practice of the invention are readily obtainable from public collections of organisms or can be isolated from a variety of environmental sources. Such environmental sources include anaerobic soils and sands, bogs, swamps, marshes, estuaries, dense algal mats, both terrestrial and marine mud and sediments, deep ocean and deep well sites, sewage and organic waste sites and treatment facilities, and animal intestinal tracts and feces. Examples of suitable organisms have been classified into four different genera within the Methanobacteria class (e.g. Methanobacterium alcaliphilum, Methanobacterium bryantii, Methanobacterium congolense, Methanobacterium defluvii, Methanobacterium espanolae, Methanobacterium formicicum, Methanobacterium ivanovii, Methanobacterium palustre, Methanobacterium thermaggregans, Methanobacterium uliginosum, Methanobrevibacter acididurans, Methanobrevibacter arboriphilicus,

Methanobrevibacter gottschalkii, Methanobrevibacter olleyae, Methanobrevibacter rum inantium, Methanobrevibacter smithii, Methanobrevibacter woesei, Methanobrevibacter wolinii, Methanothermobacter marburgensis, Methanothermobacter thermautotrophicum (also known as Methanothermobacter thermoautotroiphicus), Methanothermobacter thermoflexus, Methanothermobacter thermophilus, Methanothermobacter wolfeii,

Methanothermus sociabilis), 5 different genera within the Methanomicrobia class (e.g.

Methanocorpusculum bavaricum, Methanocorpusculum parvum, Methanoculleus

chikuoensis, Methanoculleus submarinus, Methanogenium frigidum, Methanogenium liminatans, Methanogenium marinum, Methanosarcina acetivorans, Methanosarcina barken, Methanosarcina mazei, Methanosarcina thermophila, Methanomicrobium mobile), 7 different genera within the Methanococci class (e.g. Methanocaldococcus jannaschii, Methanococcus aeolicus, Methanococcus maripaludis, Methanococcus vannielii,

Methanococcus voltaei, Methanothermococcus thermolithotrophicus, Methanocaldococcus fervens, Methanocaldococcus indicus, Methanocaldococcus infernus, Methanocaldococcus vulcanius), and one genus within the Methanopyri class (e.g. Methanopyrus kandlerϊ).

Suitable cultures are available from public culture collections (e.g. the American Type Culture Collection, the Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, and the Oregon Collection of Methanogens). In some embodiments, the methanogen is selected from the group consisting of Methanosarcinia barkeri, Methanococcus maripaludis, and Methanothermobacter thermoautotrophicus.

[0099] Additional species of methanogens suitable for purposes of the present invention include, but are not limited to, Methanobacterium formicum, Methanobrevibacter ruminantium, Methanocalculus chunghsingensis, Methanococcoides burtonii,

Methanococcus deltae, Methanocorpusculum labreanum, Methanoculleus bourgensis (Methanogenium olentangyi, Methanogenium bourgense), Methanoculleus marisnigri, Methangenium cariaci, Methanogenium organophilum, Methanopyrus kandleri,

Methanoregula boonei. In some embodiments, the biological reactor comprises a culture (e.g. monoculture or substantially pure culture) of thermophilic or hyperthermophilic microorganisms, which may also be halophiles. In some embodiments, the methanogenic microorganism is from the phylum Euryarchaeota. Examples of species of thermophilic or hyperthermophilic autotrophic methanogens suitable for the purposes of the present invention include Methanocaldococcus few ens, Methanocaldococcus indicus, Methanocaldococcus infernos, Methanocaldococcus jannaschii, Methanocaldococcus vulcanius, Methanopyrus kandleri, Methanothermobacter deβuvii, Methanothermobacter marburgensis,

Methanothermobacter thermautotrophicus, Methanothermobacter thermoflexus,

Methanothermobacter thermophϊlus, Methanothermobacter wolfeii, Methanothermococcus okinawensis, Methanothermococcus thermolithotrophicus, Methanothermus fervidus, Methanothermus sociabilis, Methanotorris formicicus, and Methanotorris igneus.

[00100] In accordance with the foregoing, in some embodiments, the methanogenic microorganisms are of the superkingdom Archaea, formerly called Archaebacteria. In certain aspects, the archaea are of the phylum: Crenarchaeota, Euryarchaeota, Korarchaeota, Nanoarchaeota, or Thaumarchaeota. In some aspects, the Crenarchaeota are of the class Thermoprotei. In some aspects, the Euryarchaeota are of the class: archaeoglobi, halobacteria, methanobacteria, methanococci, methanomicrobia, methanopyri, thermococci, thermoplasmata. In some embodiments, the Korarchaeota are of the class: Candidatus Korarchaeum or korarchaeote SRI-306. In some aspects, the Nanoarchaeota are of the class nanoarchaeum. In some aspects, the Thaumarchaeota is of the class Cenarchaeales or marine archaeal group 1.

[00101] In some embodiments, the methanogenic microorganisms are of the order:

Candidatus Korarchaeum, Nanoarchaeum, Caldisphaerales, Desulfurococcales,

Fervidicoccales, Sulfolobales, Thermoproteales, Archaeoglobales, Halobacteriales, Methanobacteriales, Methanococcales, Methanocellales, Methanomicrobiales, Methanosarcinales, Methanopyrales, Thermococcales, Thermoplasmatales, Cenarchaeales, or Nitrosopumilales.

[00102] In some embodiments, the culture comprises a classified species of the Archaea phylum Euryarchaeota, including, but not limited to, any of those set forth in Table 1. In some embodiments, the culture comprises an unclassified species of Euryarchaeota, including, but not limited to, any of those set forth in Table 2. In some embodiments, the culture comprises an unclassified species of Archaea, including, but not limited to, any of those set forth in Table 3.

[00103] In some embodiments, the culture comprises a classified species of the Archaea phylum Crenarchaeota, including but not limited to any of those set forth in Table 4. In some embodiments, the culture comprises an unclassified species of the Archaea phylum Crenarchaeota, including, but not limited to, any of those set forth in Table 5.

[00104] The archaea listed in Tables 1-5 are known in the art. See, for example, the entries for "Archaea" in the Taxonomy Browser of the National Center for Biotechnological Information (NCBI) website.

Modified Archaea

[00105] Any of the above naturally-occurring methanogenic microorganisms may be modified. Accordingly, in some embodiments, the culture of the reactor comprises methanogenic microorganisms that have been modified (e.g., adapted in culture, genetically modified) to exhibit or comprise certain characteristics or features, which, optionally, may be specific to a given growth phase (active growth phase, stationary growth phase, nearly stationary growth phase) or reactor state (e.g., dormant state, operating state). For example, in some embodiments, the culture of the reactor comprises a methanogenic microorganism that has been modified to survive and/or grow in a desired culture condition which is different from a prior culture condition in which the methanogenic microorganism survived and/or grew, e.g., the natural environment from which the microorganism was isolated, or a culture condition previously reported in literature. The desired culture conditions may differ from the prior environment in temperature, pH, pressure, cell density, volume, humidity, salt content, conductivity, carbon content, nitrogen content, vitamin-content, amino acid content, mineral-content, or a combination thereof. In some embodiments, the culture of the biological reactor comprises a methanogenic microorganism, which, before adaptation in culture or genetic modification, is one that is not a halophile and/or not a thermophile or hyperthermophile, but, through adaptation in culture or genetic modification, has become a halophile and/or thermophile or hyperthermophile. Also, for example, in some embodiments, the methano genie microorganism before genetic modification is one which does not express a protein, but through genetic modification has become a methanogenic microorganism which expresses the protein. Further, for example, in some embodiments, the methanogenic microorganism before adaptation in culture or genetic modification, is one which survives and/or grows in the presence of a particular carbon source, nitrogen source, amino acid, mineral, salt, vitamin, or combination thereof but through adaptation in culture or genetic modification, has become a methanogenic microorganism which survives and/or grows in the substantial absence thereof. Alternatively or additionally, in some embodiments, the methanogenic microorganism before adaptation in culture or genetic modification, is one which survives and/or grows in the presence of a particular amount or concentration of carbon source, nitrogen source, amino acid, mineral, salt, vitamin, but through adaptation in culture or genetic modification, has become a methanogenic microorganism which survives and/or grows in a different amount or concentration thereof.

[00106] In some embodiments, the methanogenic microorganisms are adapted to a particular growth phase or reactor state. Furthermore, for example, the methanogenic microorganism in some embodiments is one which, before adaptation in culture or genetic modification, is one which survives and/or grows in a given pH range, but through adaptation in culture becomes a methanogenic microorganism that survives and/or grows in different pH range. In some embodiments, the methanogenic microorganisms (e.g., archaea) are adapted in culture to a nearly stationary growth phase in a pH range of about 3.5 to about 10 (e.g., about 5.0 to about 8.0, about 6.0 to about 7.5). Accordingly, in some aspects, the

methanogenic microorganisms are adapted in culture to a nearly stationary growth phase at a pH of about 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2,

5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3,

7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4,

9.5, 9.6, 9.7, 9.8, 9.9, or 10.0. In some embodiments, the methanogenic microorganisms (e.g., archaea) are adapted in culture to an active growth phase in a pH range of about 6.5 to about 7.5 (e.g., about 6.8 to about 7.3). Accordingly, in some aspects, the methanogenic microorganisms are adapted in culture to a nearly stationary growth phase at a pH of about 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, or 7.5. [00107] As used herein, the term "adaptation in culture" refers to a process in which microorganisms (e.g., naturally-occurring archaea) are cultured under a set of desired culture conditions (e.g., high salinity, high temperature, substantial absence of any carbon source, low pH, etc.), which differs from prior culture conditions. The culturing under the desired conditions occurs for a period of time which is sufficient to yield modified microorganisms (progeny of the parental line (i.e. the unadapted microorganisms)) which survive and/or grow (and/or produce methane) under the desired condition(s). The period of time of adaptation in some aspects is 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 8 days, 9 days, 10 days, 11 days, 12 days, 13 days, 2 weeks, 3 weeks 4 weeks, 5 weeks, 6 weeks 1 month, 2 months, 3 months, 4 months, 5 months 6 months, 7 months, 8 months, 9 months, 10 months, 12 months, 1 year, 2 years. The process of adapting in culture selects for microorganisms that can survive and/or grow and/or produce methane in the desired culture conditions; these selected microorganisms remain in the culture, whereas the other microorganisms that cannot survive and/or grow and/or produce methane in the desired culture conditions eventually die in the culture. In some embodiments, as a result of the adaptation in culture, the methanogenic microorganisms produce methane at a higher efficiency, e.g., at a ratio of the number of carbon dioxide molecules converted to methane to the number of carbon dioxide molecules converted to cellular materials which is higher than N:l, wherein N is a number greater than 20, as further described herein.

[00108] In some embodiments, the adaptation process occurs before the microorganisms are placed in the reactor. In some embodiments, the adaptation process occurs after the microorganisms are placed in the reactor. In some embodiments, the microorganisms are adapted to a first set of conditions and then placed in the reactor, and, after placement into the biological reactor, the microorganisms are adapted to another set of conditions.

[00109] For purposes of the present invention, in some embodiments, the culture of the reactor comprises a methanogenic microorganism (e.g., archaea) which has been adapted in culture to survive and/or grow in a high salt and/or high conductivity culture medium. For example, the culture of the biological reactor comprises a methanogenic microorganism (e.g., archaea) which has been adapted in culture to survive and/or grow in a culture medium having a conductivity of about 1 to about 25 S/m.

[00110] In alternative or additional embodiments, the culture of the reactor comprises a methanogenic microorganism (e.g., archaea) which has been adapted in culture to survive and/or grow at higher temperature (e.g., a temperature which is between about 1 and about 15 degrees C greater than the temperature that the microorganisms survives and/or grows before adaptation). In exemplary embodiments, the methanogenic microorganisms are adapted to survive and/or grow in a temperature which is greater than 50 ⁰C, e.g., greater than 55 ⁰C, greater than 60 ⁰C, greater than 65 ⁰C, greater than 70 ⁰C, greater than 75 ⁰C, greater than 80 ⁰C, greater than 85 ⁰C, greater than 9O⁰C, greater than 95 ⁰C, greater than 100 ⁰C, greater than 105 ⁰C, greater than 110 ⁰C, greater than 115 ⁰C, greater than 120 ⁰C.

[00111] In some embodiments, the culture comprises a methanogenic microorganism (e.g., archaea) which has been adapted in culture to grow and/or survive in conditions which are low in or substantially absent of any vitamins. In some aspects, the culture comprises a methanogenic microorganism (e.g., archaea) which has been adapted in culture to grow and/or survive in conditions which are low in or substantially absent of any organic carbon source. In some embodiments, the culture comprises a methanogenic microorganism which has been adapted in culture to grow and/or survive in conditions with substantially reduced amounts of carbon dioxide. In these embodiments, the methanogenic microorganisms may be adapted to exhibit an increased methanogenesis efficiency, producing the same amount of methane (as compared to the unadapted microorganism) with a reduced amount of carbon dioxide. In some embodiments, the culture comprises a methanogenic microorganism which has been adapted in culture to survive in conditions which substantially lacks carbon dioxide. In these embodiments, the methanogenic microorganisms may be in a dormant phase in which the microorganisms survive but do not produce detectable levels of methane. In some embodiments, the methanogenic microorganisms have been adapted to grow and/or survive in conditions which are low in or substantially absent of any hydrogen. In some

embodiments, the methanogenic microorganisms have been adapted to grow and/or survive in conditions which are low in or substantially absent of any external source of water, e.g., the conditions do not comprise a dilution step.

[00112] In exemplary embodiments, the methanogens are adapted in culture to a nearly stationary growth phase. Such methanogens favor methane production over cell growth as measured, e.g., by the ratio of the number of CO₂ molecules converted to methane to the number of CO₂ molecules converted to cellular materials. This ratio is increased as compared to unadapted methanogens (which may exhibit, e.g., a ratio ranging from about 8:1 to about 20:1). In some embodiments, the methanogens are adapted in culture to a nearly stationary growth phase by being deprived of one or more nutrients otherwise required for optimal growth for a prolonged period of time (e.g., 1 week, 2 week, 3 weeks, 1 month, 2 months, 3 months, 4 months, 5 months, 6 months, 7 months, 8 months, 9 months, 10 months, 11 months, 1 year, 2 years, 3 years, 4 years, 5 years or more). In some embodiments, the methanogens are deprived of inorganic nutrients (e.g., hydrogen or electrons) necessary for optimum growth. In some embodiments, depriving the methanogens of hydrogen or electrons is achieved by sparging the media with an insert gas mixture such as AnCO₂ at a flow rate of 250 niL/min for several hours until neither hydrogen nor methane appear in the effluent gas stream. In some embodiments, the methanogenic microorganisms have been adapted to a nearly stationary growth phase in conditions which are low in or substantially absent of any external source of water, e.g., the adaptation conditions do not comprise a dilution step.

[00113] In some aspects, the culture comprises a methanogenic microorganism which has been adapted in culture to grow and/or survive in the culture medium set forth herein as Medium 1 and/or Medium 2 or a medium which is substantially similar to Medium 1 or Medium 2.

Genetically modified archaea

[00114] In some embodiments, the culture comprises methanogenic microorganisms which have been purposefully or intentionally genetically modified to become suitable, e.g., more suitable, for the purposes of the present invention. Suitable cultures may also be obtained by genetic modification of non-methanogenic organisms in which genes essential for supporting autotrophic methanogenesis are transferred from a methanogenic microbe or from a combination of microbes that may or may not be methanogenic on their own. Suitable genetic modification may also be obtained by enzymatic or chemical synthesis of the necessary genes.

[00115] In exemplary embodiments, a host cell that is not naturally methanogenic is intentionally genetically modified to express one or more genes that are known to be important for methanogenesis. For example, the host cell in some aspects is intentionally genetically modified to express one or more coenzymes or cof actors involved in

methanogenesis. In some specific aspects, the coenzymes or cofactors are selected from the group consisting of F420, coenzyme B, coenzyme M, methanofuran, and methanopterin, the structures of which are known in the art. In some aspects the organisms are modified to express the enzymes, well known in the art, that employ these cofactors in methanogenesis.

[00116] In some embodiments, the host cells that are intentionally modified are extreme halophiles. In other embodiments, the host cells that are intentionally modified are thermophiles or hyperthermophiles. In other embodiments, the host cells that are intentionally modified are non-autotrophic methanogens. In some aspects, the host cells that are intentionally modified are methanogens that are not autotrophic. In some aspects, the host cells that are intentionally modified are cells which are neither methanogenic nor autotrophic. In other embodiments, the host cells that are intentionally modified are host cells comprising synthetic genomes. In some aspects, the host cells that are intentionally modified are host cells which comprise a genome which is not native to the host cell.

[00117] In some embodiments, the culture comprises microorganisms that have been purposefully or intentionally genetically modified to express pili or altered pili, e.g., altered pili that promote cell adhesion to the cathode or other components of the electrobiological methanogenesis reactor or pili altered to become electrically conductive. Pili are thin filamentous protein complexes that form flexible filaments that are made of proteins called pilins. Pili traverse the outer membrane of microbial cells and can extend from the cell surface to attach to a variety of other surfaces. Pili formation facilitates such disparate and important functions as surface adhesion, cell-cell interactions that mediate processes such as aggregation, conjugation, and twitching motility. Recent in silico analyses of more than twenty archaeal genomes have identified a large number of archaeal genes that encode putative proteins resembling type IV pilins (Szabό et al. 2007, which is incorporated by reference herein in its entirety). The expression of several archaeal pilin-like proteins has since been confirmed in vivo (Wang et al. 2008; Zolghadr et al. 2007; Frδls et al. 2007, 2008, which are incorporated by reference herein in their entirety). The sequence divergence of these proteins as well as the differential expression of the operons encoding these proteins suggests they play a variety of roles in distinct biological processes.

[00118] Certain microorganisms such as Geobacter and Rhodoferax species, have highly conductive pili that can function as biologically produced nanowires as described in US 20060257985, which is incorporated by reference herein in its entirety. Many methanogenic organisms, including most of the Methanocaldococcus species and the Methanotorris species, have native pili and in some cases these pili are used for attachment. None of these organisms are known to have natively electrically conductive pili.

[00119] In certain embodiments of the present invention the pili of a methanogenic organism and/or surfaces in contact with pili of a methanogenic organism or other biological components can be altered in order to promote cell adhesion to the cathode or other components of the electrobiological methanogenesis reactor. Pili of a methanogenic organism can be further engineered to optimize their electrical conductivity. Pilin proteins can be engineered to bind to various complexes. For example, pilin proteins can be engineered to bind iron, mimicking the pili of Geobacter species or alternatively, they can be engineered to bind a low potential ferredoxin-like iron- sulfur cluster that occurs naturally in many hyperthermophilic methanogens. The desired complex for a particular application will be governed by the midpoint potential of the redox reaction.

[00120] The cells may be genetically modified, e.g., using recombinant DNA technology. For example, cell or strain variants or mutants may be prepared by introducing appropriate nucleotide changes into the organism's DNA. The changes may include, for example, deletions, insertions, or substitutions of, nucleotides within a nucleic acid sequence of interest. The changes may also include introduction of a DNA sequence that is not naturally found in the strain or cell type. One of ordinary skill in the art will readily be able to select an appropriate method depending upon the particular cell type being modified. Methods for introducing such changes are well known in the art and include, for example,

oligonucleotide-mediated mutagenesis, transposon mutagenesis, phage transduction, transformation, random mutagenesis (which may be induced by exposure to mutagenic compounds, radiation such as X-rays, UV light, etc.), PCR-mediated mutagenesis, DNA transfection, electroporation, etc.

[00121] The ability of the pili of the methanogenic organisms to adhere to the cathode coupled with an increased ability to conduct electrons, will enable the organisms to receive directly electrons passing through the cathode from the negative electrode of the power source. The use of methanogenic organisms with genetically engineered pili attached to the cathode will greatly increase the efficiency of conversion of electric power to methane.

Culture Media

[00122] The culture comprising the methanogenic microorganisms, e.g., the

methanogenic archaea, may be maintained in or on a culture medium. In some embodiments, the culture medium is a solution or suspension (e.g., an aqueous solution). In other embodiments, the culture medium is a solid or semisolid. In yet other embodiments, the culture medium comprises or is a gel, a gelatin, or a paste.

[00123] In some embodiments, the culture medium is one that encourages the active growth phase of the methanogenic microorganisms. In exemplary aspects, the culture medium comprises materials, e.g., nutrients, in non-limiting amounts that support relatively rapid growth of the microorganisms. The materials and amounts of each material of the culture medium that supports the active phase of the methanogenic microorganisms will vary depending on the species or strain of the microorganisms of the culture. However, it is within the skill of the ordinary artisan to determine the contents of culture medium suitable for supporting the active phase of the microorganisms of the culture. In some embodiments, the culture medium encourages or permits a stationary phase of the methanogenic

microorganisms. Exemplary culture medium components and concentrations are described in further detail below. Using this guidance, alternative variations can be selected for particular species for electrobiological methanogenesis in the operating state of the biological reactor using well known techniques in the field.

Inorganic materials: Inorganic elements, minerals, and salts

[00124] In some embodiments, the medium for culturing archaea comprises one or more nutrients that are inorganic elements, or salts thereof. Common inorganic elements include but are not limited to sodium, potassium, magnesium, calcium, iron, chloride, sulfur sources such as hydrogen sulfide or elemental sulfur, phosphorus sources such as phosphate and nitrogen sources such as ammonium, nitrogen gas or nitrate. Exemplary sources include NaCl, NaHCO₃, KCl, MgCl₂, MgSO₄, CaCl₂, ferrous sulfate, Na₂HPO₄, NaH₂PO₄ H₂O, H₂S, Na₂S, NH₄OH, N₂, and NaNO₃ . In some embodiments, the culture medium further comprises one or more trace elements selected from the group consisting of ions of barium, bromium, boron, cobalt, iodine, manganese, chromium, copper, nickel, selenium, vanadium, titanium, germanium, molybdenum, silicon, iron, fluorine, silver, rubidium, tin, zirconium, cadmium, zinc, tungsten and aluminum. These ions may be provided, for example, in trace element salts, such as H₃BO₃, Ba(C₂H₃O₂)₂, KBr, CoCl₂-OH₂O, KI, MnCl₂-2H₂O, Cr(SO₄)₃- 15H₂O, CuSO₄-5H₂O, NiSO₄-OH₂O, H₂SeO₃, NaVO₃, TiCl₄, GeO₂, (NH₄)6Mo₇O₂₄-4H₂O, Na₂SiO₃-9H₂O, FeSO₄-7H₂O, NaF, AgNO₃, RbCl, SnCl₂ ,ZrOCl₂-8H₂O, CdSO₄-8H₂O, ZnSO₄-7H₂O, Fe(NO₃)₃-9H₂ONa₂WO₄, AlCl₃-OH₂O.

[00125] In some embodiments, the medium comprises one or more minerals selected from the group consisting of nickel, cobalt, sodium, magnesium, iron, copper, manganese, zinc, boron, phosphorus, sulfur, nitrogen, selenium, tungsten, aluminum and potassium including any suitable non-toxic salts thereof. Thus, in some embodiments, the minerals in the medium are provided as mineral salts. Any suitable salts or hydrates may be used to make the medium. For example, and in some embodiments, the media comprises one or more of the following mineral salts: Na₃nitrilotriacetate, nitrilotriacetic acid, NiCl₂-OH₂O, CoCl₂-OH₂O, Na₂MoO₄-H₂O, MgCl₂-OH₂O, FeSO₄-H₂O, Na₂SeO₃, Na₂WO₄, KH₂PO₄, and NaCl. In some embodiments, L-cysteine may be added as a redox buffer to support early phases of growth of a low-density culture. In some embodiments, the medium comprises nickel, optionally NiCl₂-OH₂O in an amount of about 0.001 mM to about 0.01 mM, e.g. 0.002 mM, 0.003 mM, 0.004 mM, 0.005 mM, 0.006 mM, 0.007 mM, 0.008 mM, 0.009 mM, or any combination of the foregoing range endpoints. In some embodiments, the media comprises a nitrogen source, e.g., ammonium hydroxide or ammonium chloride in an amount of about 1 mM to about 10 mM, e.g. 2 mM, 3 mM, 4 mM, 5 mM, 6 mM, 7 mM, 8 mM, 9 mM, or any combination of the foregoing range endpoints. In some embodiments, the media comprises cobalt, e.g. CoCl₂-OH₂O, in an amount of about 0.001 mM to about 0.01 mM, e.g., 0.002 mM, 0.003 mM, 0.004 mM, 0.005 mM, 0.006 mM, 0.007 mM, 0.008 mM, 0.009 mM, or any combination of the foregoing range endpoints. In some embodiments, the media comprises molybdenum, a molybdenum source or molybdate, e.g. Na₂MoO₄-H₂O, in an amount of about 0.005 mM to about 0.05 mM, e.g., 0.006 mM, 0.007 mM, 0.008 mM, 0.009 mM, 0.01 mM, 0.02 mM, 0.03 mM, 0.04 mM, or any combination of the foregoing range endpoints. In some embodiments, the media comprises magnesium, e.g. MgCl₂-OH₂O, in an amount of about 0.5 mM to about 1.5 mM, e.g., 0.6 mM, 0.7 mM, 0.8 mM, 0.9 mM, 1.0 mM, 1.1 mM, 1.2 mM, 1.3 mM, 1.4 mM, or any combination of the foregoing range endpoints. In some embodiments, the media comprises iron, e.g. FeSO₄-H₂O, in an amount of about 0.05 mM to about 0.5 mM, e.g., 0.06 mM, 0.07 mM, 0.08 mM, 0.09 mM, 0.1 mM, 0.2 mM, 0.3 mM, 0.4 mM, or any combination of the foregoing range endpoints. In some embodiments, the media comprises a sulfur source or sulfate in an amount of about 0.05 mM to about 0.5 mM, e.g., 0.06 mM, 0.07 mM, 0.08 mM, 0.09 mM, 0.1 mM, 0.2 mM, 0.3 mM, 0.4 mM, or any combination of the foregoing range endpoints. In some embodiments, the media comprises selenium, a selenium source or selenate, e.g. Na₂SeO₃, in an amount of about 0.005 mM to about 0.05 mM, e.g., 0.006 mM, 0.007 mM, 0.008 mM, 0.009 mM, 0.01 mM, 0.02 mM, 0.03 mM, 0.04 mM, or any combination of the foregoing range endpoints. In some embodiments, the media comprises tungsten, a tungsten source or tungstate, e.g. Na₂WO₄, in an amount of about 0.005 mM to about 0.05 mM, e.g., 0.006 mM, 0.007 mM, 0.008 mM, 0.009 mM, 0.01 mM, 0.02 mM, 0.03 mM, 0.04 mM, or any combination of the foregoing range endpoints. In some embodiments, the media comprises potassium, e.g. KH₂PO₄, in an amount of about 5 mM to about 15 mM, e.g., 6 mM, 7 mM, 8 mM, 9 mM, 10 mM, 11 mM, 12 mM, 13 mM, 14 mM, or any combination of the foregoing range endpoints. In some embodiments, the media comprises phosphorus, a phosphorus source, or phosphate, e.g. KH₂PO₄, in an amount of about 5 niM to about 15 niM, e.g., 6 niM, 7 niM, 8 niM, 9 niM, 10 niM, 11 niM, 12 niM, 13 niM, 14 niM, or any combination of the foregoing range endpoints. In some embodiments, the media comprises NaCl in an amount of about 5 mM to about 15 mM, e.g., 6 mM, 7 mM, 8 mM, 9 mM, 10 mM, 11 mM, 12 mM, 13 mM, 14 mM, or any combination of the foregoing range endpoints.

[00126] Some archaea are extreme halophiles and prefer high salt conditions, e.g. about 1.5M to about 5.5 M NaCl, or about 3 M to about 4 M NaCl. Other archaea may be adapted to growth in higher salt conditions than their normal environment.

[00127] In some embodiments, the culture medium serves more than one purpose.

Accordingly, in some aspects, the culture medium supports the growth and/or survival of the microorganisms of the culture and serves as the cathode electrolytic medium within the reactor. An electrolyte is a substance that, when dissolved in water, permits current to flow through the solution. The conductivity (or specific conductance) of an electrolytic medium is a measure of its ability to conduct electricity. The SI unit of conductivity is Siemens per meter (S/m), and unless otherwise qualified, it is measured at a standard temperature of 25 ⁰C. Deionized water may have a conductivity of about 5.5 μS/m, while sea water has a conductivity of about 5 S/m (i.e., sea water's conductivity is one million times higher than that of deionized water).

[00128] Conductivity is traditionally determined by measuring the AC resistance of the solution between two electrodes or by torroidal inductance meters.

[00129] Limiting ion conductivity in water at 298 K for exemplary ions:

[00130] In some embodiments, the culture medium comprises a high salt concentration for purposes of increasing the conductivity of the culture medium/reactor cathode electrolyte. Conductivity is readily adjusted, for example, by adding NaCl until the desired conductivity is achieved. In some embodiments, the conductivity of the medium/electrolyte is in the range of 1 to 25 S/m (0.01 to 0.25 S/cm). This conductivity is readily achieved within the range of salt concentrations that are compatible with living methanogenic Archaea. Vitamins

[00131] In some embodiments, vitamins are substantially absent from the culture medium, to reduce contamination by non-methanogens and/or to decrease the cost of the culture medium, and thus, the overall cost of the biological reactor. However, it is possible to operate the biological reactor using media supplemented with one or more vitamins selected from the group consisting of ascorbic acid, biotin, choline chloride; D-Ca⁺⁺pantothenate, folic acid, i-inositol, menadione, niacinamide, nicotinic acid, paraaminobenzoic acid (PABA), pyridoxal, pyridoxine, riboflavin, thiamine-HCl, vitamin A acetate, vitamin Bi₂ and vitamin D₂. In some embodiments, the medium is supplemented with a vitamin that is essential to survival of the methanogenic microorganism, but other vitamins are substantially absent. Other materials

[00132] The culture medium in some embodiments comprises materials other than inorganic compounds and salts. For example, the culture medium in some embodiments, comprises a chelating agent. Suitable chelating agents are known in the art and include but not limited to nitrilotriacetic acid and/or salts thereof. Also, in some aspects, the culture medium comprises a redox buffer, e.g., Cys, to support an early active growth phase in a low- density culture.

Carbon Sources

[00133] In some aspects, the culture medium comprises a carbon source, e.g., carbon dioxide, formate, or carbon monoxide. In some embodiments, the culture medium comprises a plurality of these carbon sources in combination. Preferably, organic carbon sources are substantially absent, to reduce contamination by non-methanogens.

Nitrogen Sources

[00134] In some embodiments, the culture medium comprises a nitrogen source, e.g., ammonium, anhydrous ammonia, ammonium salts and the like. In some embodiments, the culture medium may comprise nitrate or nitrite salts as a nitrogen source, although chemically reduced nitrogen compounds are preferable. In some aspects, the culture medium

substantially lacks an organic nitrogen source, e.g., urea, corn steep liquor, casein, peptone yeast extract, and meat extract. In some embodiments diatomic nitrogen (N₂) may serve as a nitrogen source, either alone or in combination with other nitrogen sources.

Oxygen

[00135] Methanogens that are primarily anaerobic may still be capable of surviving prolonged periods of oxygen stress, e.g. exposure to ambient air for at least 6, 12, 18, or 24 hours, or 2 days, 3 days, 4 days, 5 days, 6 days, 1 week or more. Ideally, exposure to air is for 4 days or less, or 3 days or less, or 2 days or less, or 24 hours or less. Methane production may continue in the presence of oxygen concentrations as high as 2-3% of the gas phase for extended periods (at least days). However, anaerobic organisms will grow optimally in conditions of low oxygen. In some embodiments, the biological reactor substantially excludes oxygen to promote high levels of methane production.

[00136] In some embodiments, the system comprises various methods and/or features that reduce the presence of oxygen in the CO₂ stream that is fed into the biological reactor. When obligate anaerobic methanogenic microorganisms are used to catalyze methane formation, the presence of oxygen may be detrimental to the performance of the process and contaminates the product gas. Therefore, reduction of the presence of oxygen in the CO₂ stream is helpful for improving the process. In one embodiment, the oxygen is removed by pre-treatment of the gas stream in a biological reactor. In this embodiment, the reductant may be provided either by provision of a source of organic material (e.g. glucose, starch, cellulose, fermentation residue from an ethanol plant, whey residue, etc.) that can serve as substrate for an oxidative fermentation. The microbial biological catalyst is chosen to oxidatively ferment the chosen organic source, yielding CO₂ from the contaminant oxygen. In another embodiment, oxygen removal is accomplished in the main fermentation vessel via a mixed culture of microbes that includes one capable of oxidative fermentation of an added organic source in addition to the autotrophic methanogen necessary for methane production. An example of a suitable mixed culture was originally isolated as "Methanobacillus omelianskii" and is readily obtained from environmental sources (Bryant et al. Archiv Microbiol 59:20-31 (1967) "Methanobacillus omelianskii, a symbiotic association of two species of bacteria.", which is incorporated by reference herein in its entirety). In another embodiment, carbon dioxide in the input gas stream is purified away from contaminating gases, including oxygen, buy selective absorption or by membrane separation. Methods for preparing carbon dioxide sufficiently free of oxygen are well known in the art.

Exemplary media

[00137] In some embodiments, the culture medium comprises the following components: Na₃nitrilotriacetate, nitrilotriacetic acid, NiCl₂-OH₂O, CoCl₂-OH₂O, Na₂MoO₄-H₂O, MgCl₂- 6H₂O, FeSO₄-H₂O, Na₂SeO₃, Na₂WO₄, KH₂PO₄, and NaCl. In some embodiments, L- cysteine may be added as a redox buffer to support early phases of growth of a low-density culture. In some embodiments, the media comprises Na₃nitrilotriacetate (0.81 mM), nitrilotriacetic acid (0.4 niM), NiCl₂-OH₂O (0.005 niM), CoCl₂-OH₂O (0.0025 niM),

Na₂MoO₄-H₂O (0.0025 niM), MgCl₂-OH₂O (1.0 niM), FeSO₄-H₂O (0.2 niM), Na₂SeO₃

(0.001 niM), Na₂WO₄ (0.01 niM), KH₂PO₄ (10 mM), and NaCl (10 niM). L-cysteine (0.2 niM) may be included.

[00138] In some embodiments, the culture medium comprises the following components:

KH₂PO₄, NH₄Cl, NaCl, Na₃nitrilotriacetate, NiCl₂-OH₂O, CoCl₂-H₂O, Na₂MoO₄-2H₂O,

FeSO₄-7H₂O, MgCl₂-OH₂O, Na₂SeO₃, Na₂WO₄, Na₂S-9H₂O. A culture medium comprising these components may be referred to herein as Medium 1, which is capable of supporting survival and/or growth of methanogenic microorganisms originally derived from a terrestrial environment, e.g., a Methanothermobacter species. Thus, in some embodiments, the biological reactor comprises a culture of Methanothermobacter and a culture medium of

Medium 1. In some aspects , the culture medium is adjusted with NH₄OH to a pH between about 6.8 and about 7.3. In some embodiments, the culture medium not only supports growth of and/or survival of and/or methane production by the methanogenic microorganisms but also serves as the cathode electrolytic medium suitable for conducting electricity within the reactor. Accordingly, in some aspects, the conductivity of the culture medium is in the range of about 1 to about 25 S/m (about 0.01 to about 0.25 S/cm).

[00139] In some embodiments, the KH₂PO₄ is present in the medium at a concentration within the range of about 1 mM to about 100 mM, e.g., about 2 mM, about 50 mM, about 5 mM to about 20 mM.

[00140] In some embodiments, the NH₄Cl is present in the culture medium at a concentration within the range of about 10 mM to about 1500 mM, e.g., about 20 mM to about 600 mM, about 60 mM to about 250 mM.

[00141] In some embodiments, the NaCl is present in the culture medium within the range of about 1 mM to about 100 mM, e.g., about 2 mM, about 50 mM, about 5 mM to about 20 mM.

[00142] In some embodiments, the Na₃nitrilotriacetate is present in the culture medium within the range of about 0.1 mM to about 10 mM, e.g., 0.20 mM to about 6 mM, about 0.5 to about 2.5 mM.

[00143] In some embodiments, the NiCl₂-OH₂O is present in the culture medium within the range of about 0.00025 to about 0.025 mM, e.g., about 0.005 mM to about 0.0125 mM, about 0.0005 mM to about 0.005 mM. [00144] In some embodiments, the CoCl₂-H₂O is present in the culture medium within the range of about 0.0005 mM to about 0.05 mM, e.g., about 0.001 mM to about 0.025 mM, about 0.0025 mM to about 0.01 mM.

[00145] In some embodiments, the Na₂Moθ₄-2H₂O is present in the culture medium within the range of about 0.00025 mM to about 0.025 mM, e.g., about 0.0005 mM to about

0.0125 mM, about 0.00125 mM to about 0.005 mM.

[00146] In some embodiments, the FeSO₄-VH₂O is present in the culture medium within the range of about 0.02 mM to about 2 mM, e.g., about 0.04 mM to about 1 mM, about 0.1 mM to about 0.4 mM.

[00147] In some embodiments, the MgCl₂-OH₂O is present in the culture medium within the range of about 0.1 mM to about 10 mM, e.g., about 0.2 mM to about 5 mM, about 0.5 mM to about 2 mM.

[00148] In some embodiments, the Na₂SeO₃ is present in the culture medium within the range of about 0.0001 mM to about 0.01 mM, e.g., about 0.0002 mM to about 0.005 mM, about 0.0005 mM to about 0.002 mM.

[00149] In some embodiments, the Na₂WO₄ is present in the culture medium within the range of about 0.001 mM to about 0.1 mM, e.g., about 0.05 mM to about 0.05 mM, about

0.005 mM to about 0.02 mM.

[00150] In some embodiments, Medium 1 is supplemented with components, such as sulfide, that support the active growth phase or relatively rapid multiplication of the microorganism. Accordingly, in some aspects, the culture medium comprises a higher sulfide concentration, e.g. 0.1 mM to about 10 mM (e.g., about 0.2 mM to about 5 mM, about

0.5 mM to about 2 mM), about 0.5 to 5 mM, or about 1 mM Na2S-9H2O, and preferably greater than 0.01 mM Na2S-9H2O, optionally with a pH between about 6.8 and about 7.0. In other embodiments, Medium 1 supports the inactive or stationary or nearly- stationary growth phase of the microorganism and the medium comprises a lower sulfide concentration.

Accordingly, in some aspects, the culture comprises about 0.01 mM or less Na2S-9H2O, and not 1 mM Na2S-9H2O. optionally with a pH between about 7.2 and about 7.4.

[00151] In some embodiments, the culture medium comprises the following components:

KH₂PO₄, NaCl, NH₄Cl, Na₂CO₃, CaCl₂ x 2H₂O, MgCl₂ x 6H₂O, FeCl₂ x 4H₂O, NiCl₂ x

6H₂O, Na₂SeO₃ x 5 H₂O, Na₂WO₄ x H₂O, MnCl₂ x 4H₂O, ZnCl₂, H₃BO₃, CoCl₂ x 6H₂O,

CuCl₂ x 2H₂O, Na₂MoO₄ x 2H₂O, Nitrilotriacetic acid, Na₃nitrilotriacetic acid, KA1(SO₄)₂ x

12 H₂O, Na₂S x 9H₂O. A culture medium comprising these components may be referred to herein as Medium 2, which is capable of supporting survival and/or growth of methanogenic microorganisms originally derived from a marine environment, e.g., a Methanocaldooccus species, Methanotorris species, Methanopyrus species, or Methanothermococcus species. In some aspects , the culture medium is adjusted with NH₄OH to a pH between about 6.3 and about 6.8 (e.g., about 6.4 to about 6.6). In some embodiments, the culture medium not only supports growth of and/or survival of and/or methane production by the methanogenic microorganisms but also serves as the cathode electrolytic medium suitable for conducting electricity within the reactor. Accordingly, in some aspects, the conductivity of the culture medium is in the range of about 1 to about 25 S/m (about 0.01 to about 0.25 S/cm).

[00152] In some embodiments, the KH₂PO₄ is present in the culture medium at a concentration within the range of about 0.35 mM to about 37 mM, e.g., about 0.7 mM to about 0.75 mM, about 1.75 mM to about 7.5 mM.

[00153] In some embodiments, the NaCl is present in the culture medium at a

concentration within the range of about 17 mM to about 1750 mM, e.g., about 30 mM to about 860 mM, about 80 mM to about 350 mM.

[00154] In some embodiments, the NH₄Cl is present in the culture medium at a concentration within the range of about 0.7 mM to about 750 mM, e.g., about 1.5 mM to about 40 mM, about 3.75 mM to about 15 mM.

[00155] In some embodiments, the Na₂CO₃ is present in the culture medium at a concentration within the range of about 5 mM to about 600 mM, e.g., 10 mM to about 300 mM, about 30 mM to about 150 mM.

[00156] In some embodiments, the CaCl₂ x 2H₂O is present in the culture medium at a concentration within the range of about 0.05 to about 50 mM, e.g., 0.2 mM to about 5 mM, about 0.5 mM to about 2 mM.

[00157] In some embodiments, the MgCl₂ x 6H₂O is present in the culture medium at a concentration within the range of about 3 mM to about 350 mM, e.g., about 6.5 mM to about

175 mM, about 15 mM to about 70 mM.

[00158] In some embodiments, the FeCl₂ x 4H₂O is present in the culture medium at a concentration within the range of about 0.003 mM to about 0.3 mM, e.g., about 0.006 mM to about 0.15 mM, about 0.015 mM to about 0.06 mM.

[00159] In some embodiments, the NiCl₂ x 6H₂O is present in the culture medium at a concentration within the range of about 0.0005 mM to about 0.007 mM, e.g., 0.0012 mM to about 0.03 mM, about 0.003 mM to about 0.012 mM. [00160] In some embodiments, the Na₂SeO₃ x 5 H₂O is present in the culture medium at a concentration within the range of about 0.0001 mM to about 0.01 mM, e.g., about 0.00025 mM to about 0.01 mM, about 0.001 mM to about 0.005 mM.

[00161] In some embodiments, the Na₂WO₄ x H₂O is present in the culture medium at a concentration within the range of about 0.0005 mM to about 0.007 mM, e.g., 0.0012 mM to about 0.03 mM, about 0.003 mM to about 0.012 mM.

[00162] In some embodiments, the MnCl₂ x 4H₂O is present in the culture medium at a concentration within the range of about 0.003 mM to about 0.4 mM, e.g., about 0.08 mM to about 2 mM, about 0.02 mM to about 0.08 mM.

[00163] In some embodiments, the ZnCl₂ is present in the culture medium at a

concentration within the range of about 0.0005 mM to about 0.007 mM, e.g., 0.0012 mM to about 0.03 mM, about 0.003 mM to about 0.012 mM.

[00164] In some embodiments, the H₃BO₃ is present in the culture medium at a concentration within the range of about 0.0001 mM to about 0.01 mM, e.g., about 0.00025 mM to about 0.01 mM, about 0.001 mM to about 0.005 mM.

[00165] In some embodiments, the CoCi₂ x 6H₂O is present in the culture medium at a concentration within the range of about 0.0005 mM to about 0.007 mM, e.g., 0.0012 mM to about 0.03 mM, about 0.003 mM to about 0.012 mM.

[00166] In some embodiments, the CuCl₂ x 2H₂O is present in the culture medium at a concentration within the range of about 0.00004 mM to about 0.004 mM, e.g., 0.00008 mM to about 0.002 mM, about 0.0002 mM to about 0.0008 mM.

[00167] In some embodiments, the Na₂MoO₄ x 2H₂O is present in the culture medium at a concentration within the range of about 0.00004 mM to about 0.004 mM, e.g., 0.00008 mM to about 0.002 mM, about 0.0002 mM to about 0.0008 mM.

[00168] In some embodiments, the Nitrilotriacetic acid is present in the culture medium at a concentration within the range of about 0.003 mM to about 0.7 mM, e.g., about 0.12 mM to about 0.3 mM, about 0.03 mM to about 0.12 mM.

[00169] In some embodiments, the Na₃nitrilotriacetic acid is present in the culture medium at a concentration within the range of about 0.002 mM to about 0.2 mM, e.g., about

0.004 mM to about 0.1 mM, about 0.01 mM to about 0.04 mM.

[00170] In some embodiments, the KA1(SO₄)₂ x 12 H₂O is present in the culture medium at a concentration within the range of about 0.00004 mM to about 0.004 mM, e.g., 0.00008 mM to about 0.002 mM, about 0.0002 mM to about 0.0008 mM. [00171] In some embodiments, the salt concentration in Medium 2 is adjusted upward to the range of 400 to 800 mM for formulation of the electrolyte in the reactor. Additionally, the sulfide concentration of relatively stationary cultures is adjusted downward to the range of <0.01mM (<lppm sulfide in the exit gas stream).

[00172] In some examples, the media is sparged with a H2:CO2 gas mixture in a 4:1 ratio. The gas mixture can, in some embodiments, be generated with mass flow controllers at a total flow of 250 ml/minute. In some embodiments, the medium should be replenished at a rate suitable to maintain a useful concentration of essential minerals and to eliminate any metabolic products that may inhibit methanogenesis. Dilution rates below 0.1 culture volume per hour are suitable, since they yield high volumetric concentrations of active methane generation capacity.

Culture Conditions

Temperature

[00173] In some embodiments, the temperature of the culture is maintained near the optimum temperature for growth of the organism used in the culture (e.g. about 35⁰C to about 37⁰C for mesophilic organisms such as Methanosarcinia barken and Methanococcus maripaludis or about 6O⁰C to about 65⁰C for thermophiles such as Methanothermobacter thermoautotrophicus, and about 85⁰C to about 9O⁰C for organisms such as

Methanocaldococcus jannaschii, Methanocaldococcus fervens, Methanocaldococcus indicus, Methanocaldococcus infernus, and Methanocaldococcus vulcanius). However, it is envisioned that temperatures above or below the temperatures for optimal growth may be used. In fact, higher conversion rates of methane may be obtained at temperatures above the optimal growth rate temperature. Temperatures of about 50 ⁰C or higher are contemplated, e.g., about 51 ⁰C or higher, about 52 ⁰C or higher, about 53⁰C or higher, about 54 ⁰C or higher, about 55 ⁰C or higher, about 56⁰C or higher, about 57 ⁰C or higher, about 58 ⁰C or higher, about 59 ⁰C or higher, about 6O⁰C to about 15O⁰C, about 6O⁰C to about 12O⁰C, about 6O⁰C to about 100⁰C, about 6O⁰C to about 8O⁰C. Temperatures of about 4O⁰C or higher, or about 5O⁰C or higher are contemplated, e.g. about 4O⁰C to about 15O⁰C, about 5O⁰C to about 15O⁰C, about 4O⁰C to about 12O⁰C, about 5O⁰C to about 12O⁰C, about 4O⁰C to about 100⁰C, or about 5O⁰C to about 100⁰C.

[00174] In view of the foregoing, the temperature at which the culture is maintained may be considered as a description of the methanogenic microorganisms contemplated herein. For example, when the temperature of the culture is maintained at a temperature between 55 ⁰C and 12O⁰C, the methanogenic microorganism is considered as one that can be cultured at this temperature. Accordingly, the methanogenic microorganism in some embodiments is a thermophile or a hyperthermophile. In some aspects, the culture of the biological reactor comprises an autotrophic thermophilic methanogenic microorganism or an autotrophic hyperthermophilic methanogenic microorganism. In some aspects, the culture of the biological reactor comprises an autotrophic thermophilic methanogenic microorganism or an autotrophic hyperthermophilic methanogenic microorganism, either of which is tolerant to high conductivity culture medium (e.g., about 1 to about 25 S/m), as described herein, e.g., a halophile.

[00175] Archaea may be capable of surviving extended periods at suboptimal

temperatures. In some embodiments, a culture of archaea can naturally survive or are adapted to survive at room temperature (e.g. 22-28 ⁰C) for a period of at least 3 weeks to 1, 2, 3, 4, 5 or 6 months.

[00176] In some embodiments, the organisms in the culture are not mesophilic. In some embodiments, the culture is not maintained at a temperature below or about 37 ⁰C. With respect to thermophilic organisms (including, but not limited to, Methanothermobacter thermoautotrophicus, Methanocaldococcus jannaschii, Methanocaldococcus fervens, Methanocaldococcus indicus, Methanocaldococcus infernus, and Methanocaldococcus vulcanius), in some embodiments, the temperature of the culture is e.g. about 6O⁰C to about 15O⁰C, about 6O⁰C to about 12O⁰C, about 6O⁰C to about 100⁰C, or about 6O⁰C to about 8O⁰C.

[00177] Archaea can also survive under a wide range of pH conditions. In some embodiments, the pH of the culture comprising methanogenic microorganisms is between about 3.5 and about 10.0, although for growth conditions, the pH may be between about 6.5 and about 7.5. For example, the pH of the culture may be about 3.5, about 3.6., about 3.7, about 3.8, about 3.9, about 4.0, about 4.5, about 5.0, about 5.5, about 6.0, about 6.5, about 7.0, about 7.5, about 8.0, about 8.5, about 9.0, about 9.5, about 10.0. In some embodiments, the pH of the media is acidic, e.g. about 0.1 to about 5.5, about 0.1 to about 4, about 0.1 to about 3, about 1 to about 3, or about 2 to about 3. In some embodiments, the pH of the media is close to neutral, e.g. about 6 to about 8. In some embodiments, the pH of the media is alkaline, e.g. about 8.5 to about 11, or about 8 to about 10. The pH of the media can be altered by means known in the art. For example, the pH can be controlled by sparging CO₂ and/or by adding acid (e.g., HCL) or base (e.g., NaOH or NH₄OH) as needed. Pressure

[00178] In some embodiments, suitably pressures within the biological reactor range from about 0.5 atmospheres to about 500 atmospheres. The biological reactor can also contain a source of intermittent agitation of the culture. Also in one embodiment, the methane gas removed from the biological reactor suitably comprises less than about 450 ppm hydrogen sulfide, or alternatively less than about 400 ppm, 300 ppm, 200 ppm, 150 ppm, 100 ppm, 50 ppm or 20 ppm of hydrogen sulfide. Total gas delivery rates (CO₂) in the range of 0.2 to 4 volume of gas (STP) per volume of culture per minute are suitable, since they both maintain and exploit high volumetric concentrations of active methane generation capacity. In one embodiment, the redox potential is maintained below -100 mV or lower during

methanogenesis. The method of the present invention encompasses conditions in which the redox potential is transiently increased to above -100 MV, as for example when air is added to the system.

Culture Containers

[00179] A biological reactor, also known as a fermentor vessel, bioreactor, or simply reactor, as set forth herein may be any suitable vessel in which methanogenesis can take place. Suitable biological reactors to be used in the present invention should be sized relative to the volume of the CO₂ source. Typical streams of 2,200,000 Ib CO₂/day from a

100,000,000 gal/yr ethanol plant would require a CO₂ recovery/methane production fermentor of about 750,000 gal total capacity. Fermentor vessels similar to the 750,000 gal individual fermentor units installed in such an ethanol plant would be suitable.

Culture Volume and Density

[00180] The concentration of living cells in the culture medium (culture density) is in some embodiments maintained above 1 g dry weight/L. In certain embodiments, the density may be 30 g dry weight/L or higher. The volume of the culture is based upon the pore volume within the porous cathode structure within the reactor, plus any volume needed to fill any ancillary components of the reactor system, such as pumps and liquid/gas separators. Culture Medium For Reducing Contamination By Non-Methanogens

[00181] The term "non-methanogen" as used herein refers to any microorganism that is not a methanogen or is not a host cell expressing genes that permit methanogenesis. For example, in some embodiments, the archaea are cultured under conditions wherein the temperature, pH, salinity, sulfide concentration, carbon source, hydrogen concentration or electric source is altered such that growth of non-methanogens is significantly retarded under such conditions. For example, in some embodiments, the methanogens are cultured at a temperature that is higher than 37 ⁰C. In some aspects, the methano genie microorganisms are cultured at a temperature of at least 50⁰C or higher, as discussed herein, e.g., 100⁰C or more, to avoid contamination by mesophilic non-methanogens. In other embodiments, the methanogens are cultured under conditions of high salinity (e.g., >75%) to avoid

contamination by non-methanogens that are not capable of growing under high salt conditions. In still other embodiments, the methanogens are cultured under conditions in which the pH of the culture media is altered to be more acidic or more basic in order to reduce or eliminate contamination by non-methanogens that are not capable of growing under such conditions.

[00182] Contamination by non-methanogens can also be accomplished by minimizing amounts of organic carbon nutrients (e.g., sugars, fatty acids, oils, etc.) in the media. For example, in some embodiments, organic nutrients are substantially absent from the medium.

[00183] In some embodiments, components required for the growth of non-methanogenic organisms are substantially absent from the media. Such components include, but are not limited to, one or more organic carbon sources, and/or one or more organic nitrogen sources, and/or one or more vitamins. In some embodiments, formate, acetate, ethanol, methanol, methylamine, and any other metabolically available organic materials are substantially absent from the media.

[00184] In some embodiments, high salt conditions that permit survival of methanogens can retard growth of contaminating organisms.

[00185] In some embodiments, high temperatures that permit survival of methanogens can retard growth of contaminating organisms.

[00186] The term "substantially lacks" or "substantially absent" or "substantially excludes" as used herein refers to the qualitative condition of lacking an amount of a particular component significant enough to contribute to the desired function (e.g. growth of microorganisms, production of methane). In some embodiments, the term "substantially lacks" when applied to a given component of the media means that the media contains less than 5%, 4%, 3%, 2%, 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1% or less of that component. In some embodiments, the media does not contain detectable amounts of a given component.

Kits [00187] The present invention further provides kits comprising any one or a combination of: a culture comprising methanogenic microorganisms, a reactor, and a culture medium. The culture of the kit may be in accordance with any of the teachings on cultures described herein. In exemplary embodiments, the kit comprises a culture comprising an adapted strain of methanogenic microorganisms that are capable of growth and/or survival under high temperature conditions (e.g., above about 50 ⁰C, as further described herein), high salt or high conductivity conditions (as further described herein). In some embodiments, the kit comprises only the methanogenic microorganisms. The culture medium of the kits may be in accordance with any of the teachings on culture medium described herein. In some embodiments, the kit comprises a culture medium comprising the components of Medium 1 or comprising the components of Medium 2, as described herein. In some embodiments, the kit comprises only the culture medium. In certain of these aspects, the kit may comprise the reactor comprising an anode and cathode. The reactor may be in accordance with any of the teachings of reactors described herein.

III. Implementations and Applications of the System

[00188] The biological reactor according to any of the embodiments discussed above may be used in a variety of implementations or applications, such as are illustrated in Figs. 13 and 14.

[00189] For example, a biological reactor may be used as part of a stand-alone system 500, as illustrated in Fig. 13. The system 500 may be used to provide multiple energy sources (e.g., electricity and methane), or to store electrical energy produced during favorable conditions as other energy resources (e.g., methane) for use when electrical energy cannot be generated at required levels. Such a stand-alone system 500 may be particularly useful in processing spatially or temporally stranded electricity where or when this electricity does not have preferable markets.

[00190] The system 500 may include a biological reactor 502 coupled to one or more electricity sources, for example a carbon-based power plant (e.g., coal-fired power plant, natural gas-fired power plant, or biomass-fired power plant) 504, a wind-powered turbine 506, water-powered turbine 508, a fuel cell 510, solar thermal system 512 or photovoltaic system 514, or a nuclear power plant 516. It will be recognized that other sources of electricity (e.g., a geothermal power source, or a capacitor or super capacitor used for energy storage) may be used in addition to or in substitution for those illustrated. According to one embodiment, the biological reactor 502 may be coupled directly to carbon-based power plant 504, nuclear power plant 516, or other power plant that may not be able to ramp power production up or down without significant costs and/or delays, and in such a system the biological reactor 502 uses surplus electricity to convert carbon dioxide into methane that can be used in a generator to produce sufficient electricity to meet additional demands.

According to another embodiment, the biological reactor 502 may use surplus electricity (electricity that is not needed for other purposes) generated by one or more of the sources 506, 508, 510, 512, 514 to convert carbon dioxide into methane to be used in a generator to produce electricity when wind, water, solar or other conditions are unfavorable to produce electricity or to produce sufficient electricity to meet demands.

[00191] As is also illustrated in Fig. 13, the biological reactor 502 may be coupled to one or more carbon dioxide sources, for example one or more carbon-based power plants (e.g., coal-fired power plant, natural gas-fired power plant, biomass-fired power plant, or carbon- based fuel cells, which may be used as heating and power co-generation facilities or as dedicated factory power facilities) 520, which plants may be the same as or different from the plant 504. Alternatively, the stand-alone system 500 may be disposed in the vicinity of an industrial plant that provides carbon dioxide as an byproduct or a waste product, including ethanol manufacturing plants (e.g., fuel ethanol fermentation facilities) 522, industrial manufacturing plants (e.g., cement manufacturing plants or chemical manufacturing facilities) 524, commercial manufacturing plants (e.g., breweries) 526, and petrochemical refineries 528. While such significant point source emissions may serve well as a source of carbon dioxide for the biological reactor 502, it may also be possible to use atmospheric sources 530 as well (by using a carbon dioxide adsorption/desorption systems to capture atmospheric carbon dioxide, for example). As a further alternative, the carbon dioxide may be stored for use in the biological reactor (e.g., a stored source 532).

[00192] Where a significant point source of emissions is used as the carbon dioxide source (e.g., sources 520, 522, 524, 526, 528), the carbon dioxide emissions may be diverted into the biological reactor 502 to produce methane when electric power is available at prices below a pre-determined threshold. When electric power is above the pre-determined threshold, the carbon dioxide emissions may instead be emitted to the atmosphere, or it may be stored (as represented by the source 532) for later utilization in the biological reactor 502.

[00193] According to certain embodiments, the carbon dioxide from a point emission source may be commingled with other gases, including carbon monoxide, hydrogen, hydrogen sulfide, nitrogen, or oxygen or other gases common to industrial processes, or it may be substantially pure. The mixture of gases can be delivered directly to the biological reactor 502, or the carbon dioxide may be separated from the gaseous mixture before delivery to the biological reactor 502. Such sources of mixed gases include landfills, trash-to-energy facilities, municipal or industrial solid waste facilities, anaerobic digesters, concentrated animal feeding operations, natural gas wells, and facilities for purifying natural gas, which sources may be considered along side the illustrated sources 520, 522, 524, 526, 528, 530, 532.

[00194] In operation, electricity and carbon dioxide may be delivered to the biological reactor 502 continuously to maintain a desired output of methane. Alternatively, the delivery rate of the electrical current, the carbon dioxide, or water to the biological reactor 502 may be varied which may cause the rate of methane production to vary. The variations in electrical current, carbon dioxide, and water may vary according to design (to modulate the rate of methane production in response to greater or lesser demand) or as the availability of these inputs varies.

[00195] As is also illustrated in Fig. 13, the system 500 may include certain postprocessing equipment 540 associated with the biological reactor 502. For example, depending on the nature of the biological reactor 502, the flow of material exiting the first (cathode) chamber may be sent to a liquid-gas separator. Alternatively, it may be necessary to process the methane from a gaseous form into a liquid form, which may be more convenient for purposes of storage or transport. According to still further embodiments, the gas may need to be filtered to remove byproducts, which byproducts may be stored or transported separately or may be disposed of as waste material. In any event, the methane produced by the biological reactor may be sent to a storage site 550, or optionally to a distribution or transportation system 552 such as is discussed in detail with reference to the system illustrated in Fig. 14. The methane may also be used locally, for example to replace natural gas in local operations for heat, or in chemical production.

[00196] It will be recognized that while the discussion has focused on methane as the primary product of the reactor 502, the reactor 502 also will produce oxygen, which may be referred to as a secondary product or as a byproduct. Oxygen may be stored or transported in the same fashion as methane, and as such a parallel storage site and/or distribution system may be established for the oxygen generated as well. As one such example, the oxygen may be used locally, for example to enhance the efficiency of combustion and/or fuel cell energy conversion.

[00197] In the alternative to a stand-alone implementation, an integrated system 600 may be provided wherein a reactor 602 is coupled to an electrical power distribution grid 604, or power grid for short, as illustrated in Fig. 14. The power grid 604 may connect to a source of electricity 606, for example one or more power plants discussed above, such as a carbon- based power plant (e.g., coal-fired power plant, natural gas-fired power plant, or biomass- fired power plant), a wind-powered turbine, water-powered turbine, a fuel cell, solar thermal system or photovoltaic system, or a nuclear power plant. These plants 606 may be connected, via transmission substations 608 and high-voltage transmission lines 610, to power substations 612 and associated local distribution grids 614. A local distribution grid 614 may be connected to one or more biological reactors 602 according to the present disclosure via an induction circuit 616.

[00198] As noted above, certain of these power plants, such as those combusting the carbon-based fuels, operate most efficiently at steady state (i.e., ramping power production up or down causes significant costs and/or delays). The power grid may also be connected to power plants that have a variable output, such as the wind-powered and water-powered turbines and the solar- thermal and photovoltaic systems. Additionally, power users have variable demand. As such, the electricity that power producers with the lowest marginal operating expenses desire to supply to the grid 604 can, and typically does, exceed demand during extended periods (so called off-peak periods). During those periods, the excess capacity can be used by one or more biological reactors 602 according to the present disclosure to produce methane.

[00199] As also noted above, the biological reactor 602 may be coupled to one or more carbon dioxide sources 620, for example including carbon-based power plants (e.g., coal- fired power plant, natural gas-fired power plant, biomass-fired power plant, or carbon-based fuel cells). Alternatively, the system 600 may be disposed near an industrial plant that provides carbon dioxide as a byproduct or a waste product, or may use atmospheric sources of carbon dioxide or stored carbon dioxide. In fact, while it may be possible to have a readily available source of carbon dioxide for conversion into methane when off-peak electricity is also available, it might also be necessary to store carbon dioxide during non-off-peak (or peak) periods for later conversion when the electricity is available. For example, an industrial source of carbon dioxide may typically generate most of its carbon dioxide during daylight hours, which may coincide with the typical peak demand period for electricity, causing some manner of storage to be required so that sufficient carbon dioxide is available to be used in conjunction with off-peak electricity production. Simple and inexpensive, gas impermeable tanks may be sufficient for such storage for short periods of time, such as part of a day or for several days. As to such storage issues for longer periods or for larger volumes, considerable effort is presently being devoted to sequestration of carbon dioxide in underground storage sites, and it may be possible to utilize the sequestered carbon dioxide stored in such sites as the source 620 of carbon dioxide for use in the biological reactors 602 according to the present disclosure.

[00200] As was the case with the system 500, the system 600 may include optional postprocessing equipment 630 that is used to separate or treat the methane produced in the reactor 602 as required. The methane may be directed from the biological reactor 602 (with or without post-processing) into one or more containment vessels 640. In fact, the methane may be stored in aboveground storage tanks, or transported via local or interstate natural gas pipelines to underground storage locations, or reservoirs, such as depleted gas reservoirs, aquifers, and salt caverns. Additionally, the methane may be liquefied for even more compact storage, in particular where the biological reactors 602 are located where a connection to a power grid and a source of carbon dioxide are readily available, but the connection to a natural gas pipeline is uneconomical.

[00201] It will be further noted from Fig. 14 that methane may be taken from storage 640 or sent directly from the reactor 602 (optionally via the post-processing equipment 630) to a methane collection subsystem 650. From the collection subsystem 650, the methane may be introduced into a transport system 652, which system 652 may be a system of local, interstate or international pipelines for the transportation of methane, or alternatively natural gas. In this regard, the methane produced by the reactor 602 may take advantage of existing infrastructure to transport the methane from its location of production to its location of consumption. The transportation system 652 may be coupled to a distribution subsystem 654 that further facilitates its transmission to the consumer 656, which consumer may be located remote from the biological reactor 602. It will be recognized that according to certain embodiments of the present disclosure, the consumer 656 may even be one of the sources of electricity 606 connected to the power grid 604.

[00202] It will also be recognized that a biological reactor for producing methane may be useful in a closed atmospheric environment containing carbon dioxide or in which carbon dioxide is released by respiration, or other biological processes or by chemical reactions such as combustion or by a fuel cell. According to such an embodiment, the biological reactor may be operating as a stand-alone implementation (as in Fig. 13) or as part of an integrated system (as in Fig. 14). The carbon dioxide in such an environment can be combined in the biological reactor with electrical current and water to produce methane and oxygen.

Production of methane by this process may occur in a building sealed for containment purposes, or underground compartment, mine or cave or in submersible vehicle such as a submarine, or any other device or compartment that has limited access to external molecular oxygen, but sufficient electrical power, water and carbon dioxide to support the production of methane and oxygen. Oxygen produced by the biological reactor may likewise be stored as a gas, or liquefied for future use, sale or distribution.

[00203] While the foregoing examples have discussed the potential uses for methane produced by the biological reactor in meeting industrial, commercial, transportation, or residential needs (e.g., conversion into electricity through combustion in a carbon-based fuel generator or other uses, such as heating or cooking, non-combustion based conversion of methane into electricity such as via fuel cells, or chemical conversion into other compounds such as via halogenation, or reaction with other reactive species), it is also possible to appreciate the use of the biological reactor according to the present disclosure, either in a stand-alone system or as connected to a power grid, as a mechanism for carbon capture. That is, separate and apart from its uses to provide an alternative energy resource, the biological reactors according to the present disclosure may be used to remove carbon dioxide from the atmosphere, where the carbon dioxide is produced by living microorganisms, by chemical oxidation of organic material or from combustion of carbon-based fossil fuels, in particular where the carbon dioxide may be produced by large point sources such as fossil fuel power plants, cement kilns or fermentation facilities. The conversion of carbon dioxide into methane thus may produce not only methane, which has multiple other uses, but the conversion of carbon dioxide according to the present disclosure may generate or earn carbon credits for the source of the carbon dioxide, in that the carbon dioxide production of the source is decreased. These carbon credits may then be used within a regulatory scheme to offset other activities undertaken by the carbon dioxide producer, or in the life cycle of the products used or sold by the carbon dioxide producer, such as for renewable fuels derived from biomass, or gasoline refined from crude petroleum or may be used within a trading scheme to produce a separate source of revenue. Credits or offsets may be sold or conveyed in association with the methane, or oxygen, or other secondary products generated by the biological reactor or through the use of the biological reactor, or the credits may be traded independently such as on an exchange or sold directly to customers. In cases where the biological reactor functions within a business, or as part of a business contract with an entity, that uses oxygen, natural gas or methane from fossil or geologic sources, the methane produced by the biological reactor can be delivered to, or sold into a natural gas distribution system at times or in locations different from the use of natural gas and the business may retain any credits or offsets associated with the oxygen or methane produced with the biological reactor and apply such credit or offsets to natural gas or oxygen purchased from other sources and not produced directly by the biological reactor.

IV. Other Exemplary Embodiments

[00204] According to one embodiment, a method of converting carbon dioxide to methane comprises a) preparing a culture of hydrogenotrophic methanogenic archaea, b) placing the culture of hydrogenotrophic methanogenic archaea in a cathode chamber of an electrolysis chamber, the electrolysis chamber having an anode and a cathode, the cathode situated in the cathode chamber, and the cathode and anode chambers separated by a selectively permeable barrier; c) supplying carbon dioxide to the cathode chamber of the electrolysis chamber; d) supplying water to the electrolysis chamber, and e) wherein the hydrogenotrophic methanogenic archaea utilize the electrons released by the cathode and convert the carbon dioxide to methane. Additionally, step e) of such a method may only result in the production of methane gas by the hydrogenotrophic methanogenic archaea and a separate stream of oxygen gas by the anode.

[00205] According to another embodiment, a method of converting carbon dioxide to methane comprises a) preparing a culture of hydrogenotrophic methanogenic archaea; b) placing the culture of hydrogenotrophic methanogenic archaea in a cathode chamber of an electrolysis chamber, the electrolysis chamber having an anode chamber and a cathode chamber wherein the anode chamber has an anode and the cathode chamber has a cathode; c) supplying carbon dioxide to the electrolysis chamber; d) supplying water to the electrolysis chamber; e) wherein an electric potential difference is maintained between the cathode and the anode; and f) wherein the hydrogenotrophic methanogenic archaea utilize the electric potential difference between the cathode and the anode to convert the carbon dioxide to methane. According to such a method, the anode chamber and the cathode chamber may be separated by a selectively permeable barrier.

EXAMPLE 1

[00206] Vertical electrolysis chamber/cell configuration. A cylindrical electrolysis cell, 1.2 cm in internal diameter, was constructed from polusulfone plastic and arranged with an air-exposed anode on the bottom, covered by a Nafion 117 PEM and the closed cathode chamber on the top (Fig. 3). A Pt-carbon catalytic layer on a carbon mesh gas diffusion layer (GDE-LT) was used as the anode, with a titanium ring current collector around the circumference of the cell. The active area of the Nafion 117 PEM was 1.2 cm . The enclosed cathode chamber had a total internal volume of 3 ml and during operation the -1.5 ml of gas phase above the liquid phase was swept with a continuous flow (20 ml/min) of inert carrier gas. The composition of the exit gas, including any gases emitted within the cathode chamber, was analyzed continuously by mass spectrometry. The cathode electrode was constructed from reticulated vitreous carbon foam (ERG Materials and Aerospace Corp.) in the form of a cylinder, 1.2 cm diameter, 1 cm tall, placed in contact with the PEM, filling approximately half of the chamber, and connected electrically to the outside via a titanium wire. The cathode chamber was filled with 1.5 ml concentrated cell suspension, which settled into and filled the foam electrode. The carbon foam provided a high surface area for close contact between the cathode and the microorganisms. Occasionally, gas was released from bubbles formed in the solution by the addition of 5-10 microliters of antifoam agent.

[00207] Preparation of the cell suspension. Initial culture growth. Cells were grown in a continuously stirred tank fermenter, Bio Flo 110, with a total internal volume of 1.3L and a typical liquid volume of 0.6L. An initial inoculum of the autotrophic hydrogenotrophic thermophilic methanogen, Methanothermobacter thermautotrophicus, DSMZ 3590, was grown at 6O⁰C as a batch culture in a medium containing the following components:

Na3nitrilotriacetate, 0.81 mM; nitrilotriacetic acid, 0.4 mM; NiCl₂-OH₂O, 0.005 mM; CoCl₂- 6H₂O, 0.0025 mM; Na₂MoO₄-2H₂O, 0.0025 mM; MgCl₂-OH₂O, 1.0 mM; FeSO₄-7H₂O, 0.2 mM; Na₂SeO₃, 0.001 mM; Na₂WO₄, 0.01 mM; KH₂PO₄, 10 mM; NaCl, 10 mM; L-cysteine, 0.2 mM. This medium was sparged with a 4:1 H₂:CO₂ gas mixture generated with mass flow controllers at a total flow of 250 standard ml/minute. The pH of the medium was initially maintained at 6.85 via a pH stat that used 2M ammonium hydroxide to make adjustments. During the early growth phase of the culture when methane production was limited by cell concentration and increased at an exponential rate, a 0.5M sodium sulfide solution was added as needed to maintain the redox potential below -300 mV. Once the culture was grown and methane production reached a steady- state, the culture maintained the redox potential below - 450 mV on its own, using hydrogen as the reducing agent. Sulfide addition was slowed to a minimal rate (<1 ppm of H₂S in the outflow gas, as determined by mass spectrometry) needed for maintaining steady methane productivity with this strain of methanogen. Under these conditions, steady state methane production corresponds to 96-98% conversion of the input hydrogen.

[00208] Selection of a strain adapted to nearly stationary growth conditions. After steady state conditions had been established, the culture was maintained for several weeks without the addition of fresh medium. Instead, the increased volume of the culture generated by water production during methanogenesis was continually removed. The inorganic nutrients removed along with the removed medium and microorganisms were replaced from a 10Ox concentrated stock formulated as follows: Na₃nitrilotriacetate, 81 mM; nitrilotriacetic acid, 40 mM; NiCl₂-OH₂O, 0.5 mM; CoCl₂-OH₂O, 0.25 mM; Na₂MoO₄-2H₂O, 0.25 mM; MgCl₂- 6H₂O, 100 mM; FeSO₄-7H₂O, 20 mM; Na₂SeO₃, 0.1 mM; Na₂WO₄, 1.0 mM; KH₂PO₄, 1.0 M; NaCl, 1.0 M; L-cysteine, 20 mM. The goal of maintaining this extended culture under nearly stationary growth conditions was to select for a strain that could perform well and survive under conditions similar to those that are encountered in the electrolysis chamber.

[00209] Performance under electrolysis conditions. The adapted culture, at a cell concentration of 5-7g dry weight/L, was starved for energy by sparging at 250 ml/min with a 4:1 gas mixture of AnCO₂ for several hours until neither hydrogen nor methane appeared in the effluent gas stream. The cells in a sample from the culture were then concentrated threefold by centrifugation under anaerobic conditions and resuspended at a final concentration of 15-21 g dry weight/L. One and one half milliliters of this concentrated suspension was placed into the chamber and impregnated into the carbon foam cathode (Fig. 3). The cathode was polarized at a voltage of 3.0 to 4.0 V, relative to the anode, and the gasses emerging from the chamber were monitored in a 20 ml/min flow of He carrier gas. As can be seen in Fig. 15, methane is the sole gas product at voltages less than 4.0V, but a minor proportion of hydrogen gas can also be produced at higher voltages. Other possible electrochemical reaction products, such as carbon monoxide, formic acid or methanol were not detected.

[00210] Various alternative improvements. Many modifications of this setup are anticipated and intended to be within the scope of this disclosure. Expanded graphite foam or particulate graphite or other high surface to volume electrically conductive materials may be suitable as cathode electrodes. A circulating cathode solution may allow for more rapid and complete gas exchange with the outside of the electrolysis chamber. Alternative temperatures may allow for more efficient charge transfer across the membrane separating the cathode and anode chamber. Alternative materials, including composite Nafion/PTFE, may be suitable for use as the selectively permeable membrane separating the cathode and anode chambers. Alternative geometries of the chambers may improve the charge and gas transport to and from the microbes. Alternative strains of methanogenic microbes may be more tolerant of the various mechanical strains, electrical demands, and metabolite exposure present in this invention.

TABLE 1

Class Order Family Genus Species Taxonomy

ID

archaβon

Thermococci Thermococcales Thermococcaceae Palaeococcus

ferrophilus

Thermococci Thermococcales Thermococcaceae Palaeococcus Helgesonll

Thermococci Thθrmococcales Thermococcaceae Palaeococcus Sp AxOO-33

Thermococci Thermococcales Thermococcaceae Pyrococcus

abyssi

Thermococci Thermococcales Thermococcaceae Pyrococcus

Furiosus

Thermococci Thermococcales Thermococcaceae Pyrococcus

Glycovorans

Thermococci Thermococcales Thermococcaceae Pyrococcus

Horikoshii

Thermococci Thermococcales Thermococcaceae Pyrococcus Pyrococcus woesei

Pyrococcus sp

Pyrococcus sp 12/1

Pyrococcus sp 121

Pyrococcus sp 303

Pyrococcus sp 304

Pyrococcus sp 312

Pyrococcus sp 32-4

Pyrococcus sp 321

Pyrococcus sp 322

Pyrococcus sp 323

Pyrococcus sp 324

Pyrococcus sp 95-12-1

Pyrococcus sp AV5

Pyrococcus sp Ax99-7

Pyrococcus sp C2

Pyrococcus sp CH 1

Pyrococcus sp ES4

Pyrococcus sp EX2

Pyrococcus sp Fla95-Pc

Pyrococcus sp GB-3A

Pyrococcus sp GB-D

Pyrococcus sp GBD

Pyrococcus sp Gl-H

Pyrococcus sp Gl-J

Pyrococcus sp GIL

Pyrococcus sp HT3

Pyrococcus sp JT1

Pyrococcus sp MA2 31

Pyrococcus sp MA2 32

Pyrococcus sp MA2 34

Pyrococcus sp MV1019

Pyrococcus sp MV4

Pyrococcus sp MV7

Pyrococcus sp MZ14

Pyrococcus sp MZ4

Pyrococcus sp NA2

Pyrococcus sp NS102-T

Pyrococcus sp Pikanate 5017

Pyrococcus sp ST700

Pyrococcus sp Tc-2-70

Pyrococcus sp Tc95-7C-I

Pyrococcus sp TC95-7C-S

Pyrococcus sp Tc95_6

Pyrococcus sp V211

Pyrococcus sp V212

Pyrococcus sp V221

Pyrococcus sp V222

Pyrococcus sp V231

Pyrococcus sp V232

Pyrococcus sp V61

Pyrococcus sp V62

Pyrococcus sp V63

Pyrococcus sp V72

Pyrococcus sp V73

Pyrococcus sp VB112 Class Order Family Genus Species Taxonomy

ID

Pyrococcus sp VB113

Pyrococcus sp VB81

Pyrococcus sp VB82

Pyrococcus sp VB83

Pyrococcus sp VB85

Pyrococcus sp VB86

Pyrococcus sp VB93

Thermococcus Thermococcus acidaminovorans

Thermococcus aegaeus

Thθrmococcus aggregans

Thermococcus alcaliphilus

Thθrmococcus atlanticus

Thθrmococcus barophilus

Thθrmococcus barophilus MP

Thermococcus barossii

Thermococcus celer

Thθrmococcus celericrescens

Thermococcus chitonophagus

Thermococcus coalθscens

Thermococcus fumicolans

Thermococcus gammatolerans

EJ3

Thermococcus gorgonaπus

Thermococcus guaymasensis

Thermococcus hydroihermalls

Thermococcus kodakareπsis

Thermococcus kodakarensis

KOD1

Thermococcus litoralis

Thermococcus litoralis DSM 5₄73

Thermococcus marinus

Thermococcus mexicalis

Thermococcus nautilus

Thermococcus onnurineus

ThQrmococcus onnurineus NA1

Thermococcus pacificus

Thermococcus peptoπophilus

Thermococcus peptonophilus

JCM 9653

Thermococcus profundus

Thermococcus radiotolerans

Thermococcus sibiπcus

Thermococcus sibiricus MM 739

Thermococcus siculi

Thermococcus stetteri

Thθrmococcus thiorθducβns

Thermococcus waimanguensis

Thermococcus waiotapuensis

Thermococcus zilligii

Thermococcus sp

Thermococcus sp 'AEPII 1a'

Thermococcus sp 'Bio pi

O₄05IT2

Thermococcus sp 11N A5

Thermococcus sp 12-4

Thermococcus sp 13-2

Thermococcus sp 13-3

Thermococcus sp 1519

Thermococcus sp 21-1

Thermococcus sp 23-1

Thermococcus sp 23-2

Thermococcus sp 26-2

Thermococcus sp 26-3

Thermococcus sp 26/2

Thermococcus sp 28-1

Thermococcus sp 29-1

Thermococcus sp 300-Tc

Thermococcus sp 31-1

Thermococcus sp 31-3

Thermococcus sp 5-1

Thermococcus sp 70-4-2

Thermococcus sp 83-5-2 Class Order Family Genus Species Taxonomy

ID

Thermococcus sp 9N2

Thermococcus sp 9N2 20

Thermococcus sp 9N2 21

Thermococcus sp 9N3

Thermococcus sp 9oN 7

ThΘrmococcus sp A4

Thθrmococcus sp AF1T1₄ 13

Thermococcus sp AF1T1₄23

Thermococcus sp AF1T20 1 1

Thermococcus sp AF1T6 10

Thermococcus sp AF1T6 12

ThΘrmococcus sp AF1T6 63

Thermococcus sp AF2T511

Thermococcus sp Ag85-VW

Thermococcus sp AM4

Thermococcus sp AMT11

Thermococcus sp Anhetθ70-l78

Thermococcus sp Anhete70-SCI

Thermococcus sp Anhθtθ85-I78

Thermococcus sp Anhθtθ85-SCI

Thermococcus sp AT1273

Thermococcus sp AxOO-17

Thermococcus sp AxOO-27

Thermococcus sp AxOO-39

ThΘrmococcus sp AXOO-45

Thermococcus sp AxO1 -2

Thermococcus sp AxO1 -3

Thermococcus sp AxO1 -37

Thermococcus sp AxO1 -39

Thermococcus sp Ax01 -61

Thermococcus sp AxO1 -62

Thermococcus sp AxO1 -65

Thermococcus sp Ax98-43

Thermococcus sp Ax98-46

Thermococcus sp Ax98-48

Thermococcus sp AX99-47

Thermococcus sp AX99-57

Thermococcus sp AX99-67

Thermococcus sp B1

Thermococcus sp B 1001

Thermococcus sp B4

Thermococcus sp BHI60a21

Thermococcus sp BHI80a28

Thermococcus sp BHI80a40

Thermococcus sp CAR-80

Thgrmococcus sp CKU-1

Thermococcus sp CKU-199

Thermococcus sp CL1

Thermococcus sp CL2

Thermococcus sp CMI

Thermococcus sp CNR-5

Thermococcus sp CX1

Thermococcus sp CX2

Thermococcus sp CX3

Thermococcus sp CX4

Thermococcus sp CYA

Thermococcus sp Dex80a71

Thermococcus sp Dex80a75

Thermococcus sp ES1

Thermococcus sp Fθ85_1_2

Thermococcus sp GB18

Thermococcus sp GB20

Thermococcus sp GE8

Thermococcus sp Gorda2

Thermococcus sp Gorda3

Thermococcus sp Gorda4

Thermococcus sp Gorda5

Thermococcus sp Gordaθ

Thermococcus sp GT

Thermococcus sp GU5L5

Thermococcus sp HJ21

Thermococcus sp JDF-3

Thermococcus sp Kl Class Order Family Genus Species Taxonomy

ID

Thermococcus sp KS-1

Thermococcus sp KS-8

Thermococcus sp MA2 27

Thermococcus sp MA2 28

Thermococcus sp MA2 29

ThΘrmococcus sp MA2 33

Thθrmococcus sp MV1031

Thermococcus sp MV1049

Thermococcus sp MV1083

Thermococcus sp MV1092

Thermococcus sp MV1099

ThΘrmococcus sp MZ1

Thermococcus sp MZ10

Thermococcus sp MZ1 1

Thermococcus sp MZ12

Thermococcus sp MZ13

Thermococcus sp MZ2

Thermococcus sp MZ3

Thermococcus sp MZ5

Thermococcus sp MZ6

Thermococcus sp MZ8

Thermococcus sp MZ9

Thermococcus sp NS85-T

Thermococcus sp P6

ThΘrmococcus sp Pd70

Thermococcus sp Pd85

Thermococcus sp Rt3

Thermococcus sp SB611

Thermococcus sp SN531

Thermococcus sp SRB55_1

Thermococcus sp SRB70_1

Thermococcus sp SRB70_10

Thermococcus sp Tc-1 -70

Thermococcus sp Tc-1 -85

Thermococcus sp Tc-1 -95

Thermococcus sp Tc-2-85

Thermococcus sp TC-2-95

Thermococcus sp Tc-365-70

Thermococcus sp Tc-365-85

Thermococcus sp Tc-365-95

Thermococcus sp Tc-4-70

Thermococcus sp Tc-4-85

Thermococcus sp Tc-l-70

Thermococcus sp Tc-l-85

Thermococcus sp Tc-S-70

Thgrmococcus sp Tc-S-85

Thermococcus sp Tc55_1

Thermococcus sp Tc55_12

Thermococcus sp TC70-4C-I

Thermococcus sp TC70-4C-S

Thermococcus sp TC70-7C-I

Thermococcus sp TC70-7C-S

Thermococcus sp Tc70-CRC-l

Thermococcus sp TC70-CRC-S

Thermococcus sp Tc70-MC-S

Thermococcus sp Tc70-SC-l

Thermococcus sp Tc70-SC-S

Thermococcus sp Tc70-vw

Thermococcus sp Tc70_1

Thermococcus sp Tc70_10

Thermococcus sp Tc70_11

Thermococcus sp Tc70_12

Thermococcus sp Tc70_20

Thermococcus sp Tc70_6

Thermococcus sp TC7O_9

Thermococcus sp Tc85-0 age SC

Thermococcus sp Tc85-4C-I

Thermococcus sp Tc85-4C-S

Thermococcus sp Tc85-7C-S

Thermococcus sp TC85-CRC-I

Thermococcus sp TC85-CRC-S

Thermococcus sp TC85-MC-I

Thermococcus sp TC85-MC-S

Class Order Family Genus Species Taxonomy

ID

unclassified unclassified unclassified unclassified uncultured SA2 group

euryarchaeote

uncultured SA1 group

euryarchaeote

uncultured marine euryarchaeote

DH148-Y15

uncultured maπnθ euryarchaθote

DH148-Y16

uncultured marine euryarchaeote

DH148-Y19

uncultured marine euryarchaeote

DH148-Y2

uncultured marine euryarchaeote

DH148-Y4

uncultured marine euryarchaeote

DH148-Z1

uncultured marine group IV

euryarchaeote

uncultured marine group III

euryarchaeote

uncultured marine group III

euryarchaeote AD1000-40-D7

uncultured marine group III

euryarchaeote HF10_21C05

uncultured marine group III

euryarchaeote HF130_43E12

uncultured marine group III

euryarchaeote HF130_95B02

uncultured marine group III

euryarchaeote HF200_25B11

uncultured marine group III

euryarchaeote HF500 17G02

uncultured marine group III

euryarchaeotG KM3-28-E8

uncultured marinθ group III

euryarchaeote SAT1000-53-B3 uncultured marine group Il

euryarchaeote

uncultured marine group Il

euryarchaeote 37F11

uncultured marine group Il

euryarchaeote AD1000-18-D2

uncultured marine group Il

euryarchaeote DeepAnt-15E7

uncultured marine group Il

euryarchaeote DeepAnt-JyKC7 uncultured marine group Il

euryarchaeote EF100_57A08

uncultured marine group Il

euryarchaeote HF10_15F03

uncultured marine group Il

euryarchaeote HF10_15F05

uncultured marine group Il

euryarchaeote HF10_15G04

uncultured marine group Il

euryarchaeote HF10_20F02

uncultured marine group Il

euryarchaeote HF10_24E03

uncultured marine group Il

euryarchaeote HF10_25H10

uncultured marine group Il

euryarchaeote HF10_27F06

uncultured marine group Il

euryarchaeote HF10_28B09

uncultured marine group Il

euryarchaeote HF10_29E05

uncultured marine group Il

euryarchaeote HF10_30E08

uncultured marine group Il

euryarchaeote HF10_30F11

uncultured marine group Il

euryarchaeote HF10_35F06

uncultured marine group Il Class Order Family Genus Species Taxonomy

ID

euryarchaeote HF10 36B02

uncultured marine group Il

euryarchaeote HF10_39E10

uncultured marine group Il

euryarchaeote HF10_43A09

uncultured marine group Il

euryarchaθote HF10_₄8G07

uncultured marine group Il

euryarchaeote HF10_53B05

uncultured marine group Il

euryarchaeote HF10_61D03

uncultured marine group Il

euryarchaeote HF10_65D0₄

uncultured marine group Il

euryarchaeote HF10_73E12

uncultured marine group Il

euryarchaeote HF10_8H07

uncultured marine group Il

euryarchaeote HF10_90C09

uncultured marine group Il

euryarchaeote HF13CM7B12

uncultured marine group Il

euryarchaeote HF130_17D07

uncultured marine group Il

euryarchaeote HF130_21B0₄

uncultured marine group Il

euryarchaeote HF130_26G06

uncultured marine group Il

euryarchaeote HF130_27A09

uncultured marine group Il

euryarchaeote HF130_28F07

uncultured marine group Il

euryarchaeote HF130_29F10

uncultured marine group Il

euryarchaeotθ HF130_30F08

uncultured marine group Il

euryarchaeote HF130_31B11

uncultured marine group Il

euryarchaeote HF130_32D03

uncultured marine group Il

euryarchaeote HF130_33C02

uncultured marine group Il

euryarchaeote HF130_34E01

uncultured marine group Il

euryarchaeote HF130_35A10

uncultured marinθ group Il

euryarchaeotθ HF130_37H07

uncultured marine group Il

euryarchaeote HF130 40B01

uncultured marine group Il

euryarchaeote HF130_40B02

uncultured marine group Il

euryarchaeote HF130_₄OG07

uncultured marine group Il

euryarchaeote HF130 40G09

uncultured marine group Il

euryarchaeote HF130_44A02

uncultured marine group Il

euryarchaeote HF130_49F04

uncultured marine group Il

euryarchaeote HF130_4G08

uncultured marine group Il

euryarchaeote HF130_56E12

uncultured marine group Il

euryarchaeote HF130_67F08

uncultured marine group Il

euryarchaeote HF130_6E07

uncultured marine group Il

euryarchaeote HF130_71B05

uncultured marine group Il

euryarchaeote HF130_73G01

uncultured marine group Il

euryarchaeote HF130_75B06 Class Order Family Genus Species Taxonomy

ID

uncultured marine group Il

euryarchaeote HF130_76G06

uncultured marine group Il

euryarchaeote HF130_83E02

uncultured marine group Il

euryarchaeote HF130_88G10

uncultured marine group Il

euryarchaeote HF130_90E09

uncultured marine group Il

euryarchaeote HF130_9₄A03

uncultured marine group Il

euryarchaeote HF200_101 H01 uncultured marine group Il

euryarchaeote HF200_102F03 uncultured marine group Il

euryarchaeote HF200_103E03 uncultured marine group Il

euryarchaeote HF200_15F05

uncultured marine group Il

euryarchaeote HF200_25F07

uncultured marine group Il

euryarchaeote HF200_35B05

uncultured marine group Il

euryarchaeote HF200_35E02

uncultured marine group Il

euryarchaeote HF200_43D02

uncultured marine group Il

euryarchaeote HF200_44E05

uncultured marine group Il

euryarchaeote HF200_49H12

uncultured marine group Il

euryarchaeote HF200 50D06

uncultured marine group Il

euryarchaeote HF200_63E02

uncultured marine group Il

euryarchaeote HF20Q_64GQ8

uncultured marine group Il

euryarchaeote HF200_65H08

uncultured marine group Il

euryarchaeote HF200 66A10

uncultured marine group Il

euryarchaeote HF200_70E08

uncultured marine group Il

euryarchaeote HF200_71A04

uncultured marine group Il

euryarchaeote HF200_72A06

uncultured marine group Il

euryarchaeote HF200_78D05

uncultured marine group Il

euryarchaeote HF200_84A01

uncultured marine group Il

euryarchaeote HF200_89A11

uncultured marine group Il

euryarchaeote HF200_97B09

uncultured marine group Il

euryarchaeote HF500_100E05 uncultured marine group Il

euryarchaeote HF500_11G07

uncultured marine group Il

euryarchaeote HF500_22F05

uncultured marine group Il

euryarchaeote HF500_24F01

uncultured marine group Il

euryarchaeote HF500_25E08

uncultured marine group Il

euryarchaeote HF500_26A05

uncultured marine group Il

euryarchaeote HF500_30A08

uncultured marine group Il

euryarchaeote HF500_47D04

uncultured marine group Il

euryarchaeote HF500_56B09

uncultured marine group Il Class Order Family Genus Species Taxonomy

ID

euryarchaeote HF500 58A11

uncultured marine group Il

euryarchaeote HF500_67F10

uncultured marine group Il

euryarchaeote HF7CM05F02

uncultured marine group Il

euryarchaθote HF70_106D07

uncultured marine group Il

euryarchaeote HF70_1₄F12

uncultured marine group Il

euryarchaeote HF70_25A12

uncultured marine group Il

euryarchaeote HF70_39H11

uncultured marine group Il

euryarchaeote HF70_41 E01

uncultured marine group Il

euryarchaeote HF70_48A05

uncultured marine group Il

euryarchaeote HF70_48G03

uncultured marine group Il

euryarchaeote HF70_51 B02

uncultured marine group Il

euryarchaeote HF70_53G11

uncultured marine group Il

euryarchaeote HF70_59C08

uncultured marine group Il

euryarchaeote HF70_89B11

uncultured marine group Il

euryarchaeote HF70_91G08

uncultured marine group Il

euryarchaeote HF70_95E04

uncultured marine group Il

euryarchaeote HF70_97E04

uncultured marine group Il

euryarchaeotθ KM3-130-D10

uncultured marine group Il

euryarchaeote KM3-136-D10

uncultured marine group Il

euryarchaeote KM3-72-G3

uncultured marine group Il

euryarchaeote KM3-85-F5

uncultured marine group Il

euryarchaeote SAT1000-15-B12 uncultured archaeon ACE-6

uncultured archaeon BURTON-41 uncultured archaeon BURTOM-47 uncultured archaeon CLEAR-15 uncultured archaeon CLEAR-24 uncultured archaeon PENDANT- 17

uncultured archaeon PENDANT- 33

euryarchaeote J3 25-8

euryarchaeote D4 75-18

115532

euryarchaeote D4 75-4

euryarchaeote DJ3 25-13

euryarchaeote J4 75-12

euryarchaeote J4 75-15

euryarchaeote J4 75-24

euryarchaeote SvA99MeOH

euryarchaeote SvA99TMA

methanogenic archaeon CH1270 methanogenic archaeon F1/B-1 methanogenic archaeon F1/B-2 methanogenic archaeon F1/B-3 methanogenic archaeon F1/P-1 methanogenic archaeon F1/P-2 methanogenic archaeon F1/P-3 methanogenic archaeon F4/B-1 methanogenic archaeon F4/B-2 methanogenic archaeon F4/B-3

methanogenic archaeon F4/P-1

TABLE 2

TABLE 3

Name of Unclassified Species Taxonomy ID archaeoπ GSLlC 378400 archaeoπ GSLlD 378399Si a m e of U # da. s-sjf ie ύ . Sm cfe .$..

archaeoπ HR3812-Enrichment-017

archaeoπ HR3812-Eπrichmeπt-018

archaeoπ HR3812-Enrichment-019

archaeoπ HR3812-Eπrichmeπt-020

archaeoπ HR3812-Eπrichmeπt-021

archaeoπ HR3812-Enrichment-022

archaeoπ K-4a2archaeoπ K-5a2

archaeoπ LL25Alarchaeon LL25A10

archaeoπ LL25A2archaeoπ LL25A3

archaeoπ LL25A4archaeon LL25A6

archaeoπ LL25A7archaeon LL25A8

archaeoπ LL37Alarchaeoπ LL37A19

archaeoπ LL37A2archaeon LL37A20

archaeoπ LL37A29

archaeoπ LL37A3

archaeonLL37A33

archaeoπ LL37A35

archaeoπ SLl.19

archaeoπ SLl.60

archaeoπ SLl.61

archaeoπ SL2.43

archaeoπ SL2.45

archaeoπ SVAL2.51

archaeoπ SVAL2.52

archaeoπ SVAL2.53

archaeoπ SVAL2.54

archaeoπ SVAL2.55

archaeoπ SVAL2.56

archaeoπ enrichment clone M21

archaeoπ enrichment clone M33

archaeoπ enrichment culture clone 1OP

Aarchaeoπ enrichment culture clone ITP

Aarchaeoπ enrichment culture clone 2TP

Aarchaeoπ enrichment culture clone AOM-Cloπe-All

archaeon enrichment culture clone AOM-Cloπe-A2

archaeon enrichment culture clone AOM-Cloπe-B2

archaeon enrichment culture clone AOM-Cloπe-B6

archaeon enrichment culture clone AOM-Cloπe-C3

archaeon enrichment culture clone AOM-Cloπe-C9

archaeon enrichment culture clone AOM-Cloπe-DIO

archaeon enrichment culture clone AOM-Cloπe-ElO

archaeon enrichment culture clone AOM-Cloπe-E7

archaeon enrichment culture clone AOM-Cloπe-E9

archaeon enrichment culture clone AOM-Clone-F5

archaeon enrichment culture clone AOM-Clone-F9

archaeon enrichment culture clone AOM-Clone-G10

archaeon enrichment culture clone AOM-Clone-H9

archaeon enrichment culture clone ArchlO

archaeon enrichment culture clone ARQ17-JL

archaeon enrichment culture clone ARQ19-JL

archaeon enrichment culture clone ARQ2-JL

archaeon enrichment culture clone ARQ9-JL

archaeon enrichment culture clone Cl-IOC-A

archaeon enrichment culture clone Cl-IlC-A

archaeon enrichment culture clone C1-13C-A Name of Unclassified Species Taxonomy ID archaeoπ enrichment culture clone C1-16C-A

archaeon enrichment culture clone C1-18C-A

archaeon enrichment culture clone C1-19C-A

archaeon enrichment culture clone Cl-IC-A

archaeon enrichment culture clone C1-20C-A

archaeon enrichment culture clone C1-24C-A

archaeon enrichment culture clone C1-26C-A

archaeon enrichment culture clone C1-29C-A

archaeon enrichment culture clone C1-2C-A

archaeon enrichment culture clone C1-30C-A

archaeon enrichment culture clone C1-31C-A

archaeon enrichment culture clone C1-32C-A

archaeon enrichment culture clone C1-34C-A

archaeon enrichment culture clone C1-38C-A

archaeon enrichment culture clone C1-3C-A

archaeon enrichment culture clone C1-42C-A

archaeon enrichment culture clone C1-44C-A

archaeon enrichment culture clone C1-46C-A

archaeon enrichment culture clone C1-47C-A

archaeon enrichment culture clone C1-48C-A

archaeon enrichment culture clone C1-4C-A

archaeon enrichment culture clone C1-52C-A

archaeon enrichment culture clone C1-5C-A

archaeon enrichment culture clone C1-8C-A

archaeon enrichment culture clone C3-15C-A

archaeon enrichment culture clone C3-18C-A

archaeon enrichment culture clone C3-1C-A

archaeon enrichment culture clone C3-20C-A

archaeon enrichment culture clone C3-22C-A

archaeon enrichment culture clone C3-26C-A

archaeon enrichment culture clone C3-33C-A

archaeon enrichment culture clone C3-37C-A

archaeon enrichment culture clone C3-41C-A

archaeon enrichment culture clone C3-42C-A

archaeon enrichment culture clone C3-47C-A

archaeon enrichment culture clone C3-54C-A

archaeon enrichment culture clone C3-56C-A

archaeon enrichment culture clone C3-5C-A

archaeon enrichment culture clone C3-7C-A

archaeon enrichment culture clone C4-10C-A

archaeon enrichment culture clone C4-11C-A

archaeon enrichment culture clone C4-12C-A

archaeon enrichment culture clone C4-14C-A

archaeon enrichment culture clone C4-15C-A

archaeon enrichment culture clone C4-16C-A

archaeon enrichment culture clone C4-17C-A

archaeon enrichment culture clone C4-18C-A

archaeon enrichment culture clone C4-20C-A

archaeon enrichment culture clone C4-21C-A

archaeon enrichment culture clone C4-22C-A

archaeon enrichment culture clone C4-23C-A

archaeon enrichment culture clone C4-24C-A

archaeon enrichment culture clone C4-26C-A

archaeon enrichment culture clone C4-27C-A

archaeon enrichment culture clone C4-28C-A

archaeon enrichment culture clone C4-29C-A

archaeon enrichment culture clone C4-2C-A

archaeon enrichment culture clone C4-30C-A

archaeon enrichment culture clone C4-32C-A Name of Unclassified Species Taxonomy ID archaeoπ enrichment culture clone C4-34C-A

archaeon enrichment culture clone C4-35C-A

archaeon enrichment culture clone C4-37C-A

archaeon enrichment culture clone C4-38C-A

archaeon enrichment culture clone C4-3C-A

archaeon enrichment culture clone C4-40C-A

archaeon enrichment culture clone C4-41C-A

archaeon enrichment culture clone C4-42C-A

archaeon enrichment culture clone C4-43C-A

archaeon enrichment culture clone C4-45C-A

archaeon enrichment culture clone C4-46C-A

archaeon enrichment culture clone C4-47C-A

archaeon enrichment culture clone C4-48C-A

archaeon enrichment culture clone C4-49C-A

archaeon enrichment culture clone C4-4C-A

archaeon enrichment culture clone C4-50C-A

archaeon enrichment culture clone C4-51C-A

archaeon enrichment culture clone C4-52C-A

archaeon enrichment culture clone C4-54C-A

archaeon enrichment culture clone C4-6C-A

archaeon enrichment culture clone C4-8C-A

archaeon enrichment culture clone C4-9C-A

archaeon enrichment culture clone DanδO AlOE

archaeon enrichment culture clone DanδO AIlE

archaeon enrichment culture clone DanδO A12E

archaeon enrichment culture clone Dan60_A13E

archaeon enrichment culture clone Dan60_A14E

archaeon enrichment culture clone Dan60_A15E

archaeon enrichment culture clone DanδO A16E

archaeon enrichment culture clone DanδO A17E

archaeon enrichment culture clone DanδO A18E

archaeon enrichment culture clone Dan60_A19E

archaeon enrichment culture clone Dan60_AlE

archaeon enrichment culture clone Dan60_A20E

archaeon enrichment culture clone DanδO A2E

archaeon enrichment culture clone DanδO A3E

archaeon enrichment culture clone DanδO A4E

archaeon enrichment culture clone Dan60_A5E

archaeon enrichment culture clone Dan60_A6E

archaeon enrichment culture clone Dan60_A7E

archaeon enrichment culture clone DanδO A8E

archaeon enrichment culture clone DanδO A9E

archaeon enrichment culture clone Dan60S_A10E

archaeon enrichment culture clone Dan60S_AllE

archaeon enrichment culture clone Dan60S_A12E

archaeon enrichment culture clone DanδOS A13E

archaeon enrichment culture clone DanδOS A14E

archaeon enrichment culture clone DanδOS A15E

archaeon enrichment culture clone Dan60S_A16E

archaeon enrichment culture clone Dan60S_A17E

archaeon enrichment culture clone Dan60S_A18E

archaeon enrichment culture clone DanδOS A19E

archaeon enrichment culture clone DanδOS AlE

archaeon enrichment culture clone DanδOS A20E

archaeon enrichment culture clone Dan60S_A2E

archaeon enrichment culture clone Dan60S_A3E

archaeon enrichment culture clone Dan60S_A4E

archaeon enrichment culture clone DanδOS A5E

archaeon enrichment culture clone DanδOS A6E Name of Uo classified 5 pedes S Taxonomy ID archaeon enrichment culture clone Dan60S A7E

archaeon enrichment culture clone Dan60S A8E

archaeon enrichment culture clone Dan60S A9E

archaeon enrichment culture clone DGGE-IA

archaeon enrichment culture clone DGGE-2A

archaeon enrichment culture clone DGGE-4A

archaeon enrichment culture clone EA17.1

archaeon enrichment culture clone EA29.3

archaeon enrichment culture clone EA29.6

archaeon enrichment culture clone EA3.11

archaeon enrichment culture clone EA3.3

archaeon enrichment culture clone EA3.5

archaeon enrichment culture clone EA8.1

archaeon enrichment culture clone EA8.8

archaeon enrichment culture clone EA8.9

archaeon enrichment culture clone HS25 1

archaeon enrichment culture clone HS7 1

archaeon enrichment culture clone LCB A1C7

archaeon enrichment culture clone LCB A1C9

archaeon enrichment culture clone MBT-Il

archaeon enrichment culture clone McrA2

archaeon enrichment culture clone MST-4

archaeon enrichment culture clone Nye-0_2-enr40

archaeon enrichment culture clone PW15.4A

archaeon enrichment culture clone PW15.6

archaeon enrichment culture clone PW15.7A

archaeon enrichment culture clone PW20.4A

archaeon enrichment culture clone PW25.2A

archaeon enrichment culture clone PW25.9

archaeon enrichment culture clone PW30.6A

archaeon enrichment culture clone PW32.12A

archaeon enrichment culture clone PW32.5A

archaeon enrichment culture clone PW45.1

archaeon enrichment culture clone PW45.7A

archaeon enrichment culture clone PW45.9A

archaeon enrichment culture clone PW5.2A

archaeon enrichment culture clone PW54.3A

archaeon enrichment culture clone PW54.4

archaeon enrichment culture clone PW68.8A

archaeon enrichment culture clone R3-lall

archaeon enrichment culture clone R3-la2

archaeon enrichment culture clone R3-la3

archaeon enrichment culture clone R3-la6

archaeon enrichment culture clone R3-lb6

archaeon enrichment culture clone R3-ldlO

archaeon enrichment culture clone R3-le5

archaeon enrichment culture clone R3-le8

archaeon enrichment culture clone R3-lf5

archaeon enrichment culture clone R3-lg4

archaeon enrichment culture clone R3-lh9

archaeon enrichment culture clone T-RF321

archaeon enrichment culture clone VNC3A001

archaeon enrichment culture clone VNC3A005

archaeon enrichment culture clone YE25 1

archaeon enrichment culture clone YE7 1

archaeon enrichment culture clone YE7 5

archaeon enrichment culture DGGE band 1507ag 1

archaeon enrichment culture DGGE band 1507cas 1

archaeon enrichment culture DGGE band 1507cas 2 Name of Unclassified Species Taxonomy ID archaeon enrichment culture DGGE band 1510b-ker 1

archaeon enrichment culture DGGE band 1510b-ker 2

archaeon enrichment culture DGGE band 1521cmc 1

archaeon enrichment culture DGGE band 1521cmc 2

archaeon enrichment culture DGGE band 1523rope 1

archaeon enrichment culture DGGE band 1523rope 2

archaeon enrichment culture DGGE band DS13

archaeon enrichment culture DGGE band DS18

archaeon enrichment culture DGGE band DS19

methanogenic archaeon enrichment culture clone 4.17a Arc Band 1 methanogenic archaeon enrichment culture clone 4.17b Arc Band 1 methanogenic archaeon enrichment culture clone BAMC-4

methanogenic archaeon enrichment culture clone BAMC-5

methanogenic archaeon enrichment culture clone NapK-0_20-enr35 methanogenic archaeon enrichment culture clone NapK-0_20-enr36 methanogenic archaeon enrichment culture clone Napk-0_20-enr74 methanogenic archaeon enrichment culture clone NapK-80_100-enr37 toluene-degrading methanogenic consortium archaeon

uncultured ammonia-oxidizing archaeon

uncultured archaeal symbiont PAIlO

uncultured archaeal symbiont PAlIl

uncultured archaeal symbiont PA115

uncultured archaeal symbiont PA120

uncultured archaeal symbiont PA121

uncultured archaeal symbiont PA122

uncultured archaeal symbiont PA201

uncultured archaeal symbiont PA202

uncultured archaeal symbiont PA203

uncultured archaeal symbiont PA204

uncultured archaeal symbiont STlOl

uncultured archaeal symbiont ST119

uncultured archaeal symbiont ST120

uncultured archaeal symbiont ST123

uncultured archaeal symbiont ST124

uncultured archaeal symbiont ST141

uncultured archaeal symbiont ST150

uncultured archaeon

uncultured archaeon MedDCM-OCT-S02-C115

uncultured archaeon MedDCM-OCT-S04-C14

uncultured archaeon MedDCM-OCT-S04-C140

uncultured archaeon MedDCM-OCT-S04-C163

uncultured archaeon MedDCM-OCT-S04-C246

uncultured archaeon MedDCM-OCT-S05-C10

uncultured archaeon MedDCM-OCT-S05-C205

uncultured archaeon MedDCM-OCT-S05-C32

uncultured archaeon MedDCM-OCT-S05-C418

uncultured archaeon MedDCM-OCT-S05-C57

uncultured archaeon MedDCM-OCT-S05-C724

uncultured archaeon MedDCM-OCT-S06-C18

uncultured archaeon MedDCM-OCT-S08-C16

uncultured archaeon MedDCM-OCT-S08-C282

uncultured archaeon MedDCM-OCT-S08-C37

uncultured archaeon MedDCM-OCT-S08-C54

uncultured archaeon MedDCM-OCT-S08-C82

uncultured archaeon MedDCM-OCT-S08-C92

uncultured archaeon MedDCM-OCT-S09-C13

uncultured archaeon MedDCM-OCT-S09-C50

uncultured archaeon MedDCM-OCT-Sll-C441

uncultured archaeon MedDCM-OCT-Sll-C473 Name of UocfassJffed Specfes 1 Taxonomy ID uncultured archaeoπ 'Antarctica #17'

uncultured archaeon 'Norris Geyer Basin #1'

uncultured archaeon 'Norris Geyer Basin #13'

uncultured archaeon 'Norris Geyer Basin #14'

uncultured archaeon 'Norris Geyer Basin #16'

uncultured archaeon 'Norris Geyer Basin #4'

uncultured archaeon 'Norris Geyer Basin #6'

uncultured archaeon 'Norris Geyer Basin #8'

uncultured archaeon 'Norris Geyer Basin #9'

uncultured archaeon 'Obsidian Pool #1'

uncultured archaeon 'Obsidian Pool #10'

uncultured archaeon 'Obsidian Pool #3'

uncultured archaeon 'Obsidian Pool #4'

uncultured archaeon 'Obsidian Pool #6'

uncultured archaeon 'Obsidian Pool #9'

uncultured archaeon 'Queen's Laundry #28'

uncultured archaeon 101B

uncultured archaeon 102A

uncultured archaeon 103D

uncultured archaeon 112D

uncultured archaeon 113C

uncultured archaeon 130D

uncultured archaeon 142C

uncultured archaeon 145B

uncultured archaeon 15A

uncultured archaeon 17B

uncultured archaeon 19a-l

uncultured archaeon 19a-14

uncultured archaeon 19a-18

uncultured archaeon 19a-19

uncultured archaeon 19a-23

uncultured archaeon 19a-27

uncultured archaeon 19a-29

uncultured archaeon 19a-4

uncultured archaeon 19a-5

uncultured archaeon 19b-l

uncultured archaeon 19b-16

uncultured archaeon 19b-17

uncultured archaeon 19b-2

uncultured archaeon 19b-23

uncultured archaeon 19b-24

uncultured archaeon 19b-26

uncultured archaeon 19b-30

uncultured archaeon 19b-31

uncultured archaeon 19b-32

uncultured archaeon 19b-34

uncultured archaeon 19b-35

uncultured archaeon 19b-37

uncultured archaeon 19b-38

uncultured archaeon 19b-39

uncultured archaeon 19b-41

uncultured archaeon 19b-42

uncultured archaeon 19b-46

uncultured archaeon 19b-5

uncultured archaeon 19b-52

uncultured archaeon 19b-7

uncultured archaeon 19b-8

uncultured archaeon 19b-9

uncultured archaeon 19c-l Name of Unclassified Species Taxonomy ID uncultured archaeon 19c-10

uncultured archaeon 19c-12

uncultured archaeon 19c-17

uncultured archaeon 19c-18

uncultured archaeon 19c-27

uncultured archaeon 19c-31

uncultured archaeon 19c-33

uncultured archaeon 19c-35

uncultured archaeon 19c-36

uncultured archaeon 19c-45

uncultured archaeon 19c-49

uncultured archaeon 19c-5

uncultured archaeon 19c-50

uncultured archaeon 19c-51

uncultured archaeon 19c-52

uncultured archaeon 19c-53

uncultured archaeon 19c-54

uncultured archaeon 1MT315

uncultured archaeon 1MT325

uncultured archaeon 2Oa-I

uncultured archaeon 2Oa-IO

uncultured archaeon 20a-12

uncultured archaeon 20a-15

uncultured archaeon 20a-17

uncultured archaeon 20a-2

uncultured archaeon 20a-25

uncultured archaeon 20a-28

uncultured archaeon 20a-3

uncultured archaeon 20a-6

uncultured archaeon 20a-7

uncultured archaeon 20a-9

uncultured archaeon 2OB

uncultured archaeon 2Ob-I

uncultured archaeon 2Ob-IO

uncultured archaeon 20b-14

uncultured archaeon 20b-15

uncultured archaeon 20b-16

uncultured archaeon 20b-18

uncultured archaeon 20b-22

uncultured archaeon 20b-25

uncultured archaeon 20b-26

uncultured archaeon 20b-27

uncultured archaeon 20b-28

uncultured archaeon 20b-30

uncultured archaeon 20b-31

uncultured archaeon 20b-37

uncultured archaeon 20b-39

uncultured archaeon 20b-4

uncultured archaeon 20b-40

uncultured archaeon 20b-47

uncultured archaeon 20b-53

uncultured archaeon 20b-54

uncultured archaeon 20b-7

uncultured archaeon 20b-9

uncultured archaeon 2Oc-IO

uncultured archaeon 20c-12

uncultured archaeon 20c-16

uncultured archaeon 20c-17

uncultured archaeon 20c-18 Name of Unclassified Species Taxonomy ID uncultured archaeon 20c-19

uncultured archaeon 20c-20

uncultured archaeon 20c-22

uncultured archaeon 20c-23

uncultured archaeon 20c-25

uncultured archaeon 20c-29

uncultured archaeon 20c-3

uncultured archaeon 20c-37

uncultured archaeon 20c-39

uncultured archaeon 20c-4

uncultured archaeon 20c-42

uncultured archaeon 20c-43

uncultured archaeon 20c-47

uncultured archaeon 20c-52

uncultured archaeon 20c-54

uncultured archaeon 20c-8

uncultured archaeon 2OD

uncultured archaeon 22C

uncultured archaeon 26A

uncultured archaeon 27

uncultured archaeon 27A

uncultured archaeon 27D

uncultured archaeon 2C100

uncultured archaeon 2C129

uncultured archaeon 2C130

uncultured archaeon 2C169

uncultured archaeon 2C174

uncultured archaeon 2C25

uncultured archaeon 2C30

uncultured archaeon 2C300X

uncultured archaeon 2C46

uncultured archaeon 2C8

uncultured archaeon 2C82

uncultured archaeon 2C83

uncultured archaeon 2C84

uncultured archaeon 2C87

uncultured archaeon 2C9

uncultured archaeon 2MTl

uncultured archaeon 2MT103

uncultured archaeon 2MT120

uncultured archaeon 2MT16

uncultured archaeon 2MT196

uncultured archaeon 2MT198

uncultured archaeon 2MT22

uncultured archaeon 2MT310

uncultured archaeon 2MT320

uncultured archaeon 2MT53

uncultured archaeon 2MT7

uncultured archaeon 2MT8

uncultured archaeon 2MT98

uncultured archaeon 6OB

uncultured archaeon 61B

uncultured archaeon 61D

uncultured archaeon 63-Al

uncultured archaeon 63-A10

uncultured archaeon 63-A11

uncultured archaeon 63-A12

uncultured archaeon 63-A14

uncultured archaeon 63-A15 Name of Unclassified Species Taxonomy ID uncultured archaeon 63-A16

uncultured archaeon 63-A17

uncultured archaeon 63-A18

uncultured archaeon 63-A19

uncultured archaeon 63-A20

uncultured archaeon 63-A21

uncultured archaeon 63-A22

uncultured archaeon 63-A23

uncultured archaeon 63-A24

uncultured archaeon 63-A3

uncultured archaeon 63-A4

uncultured archaeon 63-A5

uncultured archaeon 63-A6

uncultured archaeon 63-A7

uncultured archaeon 63-A8

uncultured archaeon 63-A9

uncultured archaeon 63D

uncultured archaeon 64D

uncultured archaeon 65B

uncultured archaeon 65C

uncultured archaeon 66D

uncultured archaeon 7OA

uncultured archaeon 71A

uncultured archaeon 71C

uncultured archaeon 73A

uncultured archaeon 73D

uncultured archaeon 76A

uncultured archaeon 8OB

uncultured archaeon 82D

uncultured archaeon 83D

uncultured archaeon 84C

uncultured archaeon 85A

uncultured archaeon 9OC

uncultured archaeon 91B

uncultured archaeon 93A

uncultured archaeon 94B

uncultured archaeon 94D

uncultured archaeon 95A

uncultured archaeon A016

uncultured archaeon A140

uncultured archaeon A145

uncultured archaeon A148

uncultured archaeon A151

uncultured archaeon A153

uncultured archaeon A154

uncultured archaeon A157

uncultured archaeon A174

uncultured archaeon A175

uncultured archaeon A177

uncultured archaeon A178

uncultured archaeon ACAl-Ocm

uncultured archaeon ACAl-9cm

uncultured archaeon ACAIO-Ocm

uncultured archaeon ACA16-9cm

uncultured archaeon ACA17-9cm

uncultured archaeon ACA3-0cm

uncultured archaeon ACA4-0cm

uncultured archaeon AM-I

uncultured archaeon AM-10 Name of Unclassified Species Taxonomy ID uncultured archaeon AM-Il

uncultured archaeon AM-12

uncultured archaeon AM-13

uncultured archaeon AM-14

uncultured archaeon AM-15

uncultured archaeon AM-16

uncultured archaeon AM-17

uncultured archaeon AM-18

uncultured archaeon AM-19

uncultured archaeon AM-2

uncultured archaeon AM-20

uncultured archaeon AM-21

uncultured archaeon AM-22

uncultured archaeon AM-3

uncultured archaeon AM-4

uncultured archaeon AM-5

uncultured archaeon AM-6

uncultured archaeon AM-7

uncultured archaeon AM-8

uncultured archaeon AM-9

uncultured archaeon APAl-Ocm

uncultured archaeon APA2-17cm

uncultured archaeon APA3-0cm

uncultured archaeon APA3-llcm

uncultured archaeon APA4-0cm

uncultured archaeon APA6-17cm

uncultured archaeon APA7-17cm

uncultured archaeon Ar21

uncultured archaeon Ar26

uncultured archaeon Ar28

uncultured archaeon Arc.l

uncultured archaeon Arc.118

uncultured archaeon Arc.119

uncultured archaeon Arc.148

uncultured archaeon Arc.168

uncultured archaeon Arc.171

uncultured archaeon Arc.2

uncultured archaeon Arc.201

uncultured archaeon Arc.212

uncultured archaeon Arc.22

uncultured archaeon Arc.3

uncultured archaeon Arc.4

uncultured archaeon Arc.43

uncultured archaeon Arc.75

uncultured archaeon Arc.9

uncultured archaeon Arc.98

uncultured archaeon Casl4#l

uncultured archaeon Casl4#2

uncultured archaeon Casl4#3

uncultured archaeon Casl4#4

uncultured archaeon Casl4#5

uncultured archaeon Casl4#6

uncultured archaeon Casl8#l

uncultured archaeon Casl8#2

uncultured archaeon Casl8#3

uncultured archaeon Casl8#4

uncultured archaeon Casl9#l

uncultured archaeon Casl9#2

uncultured archaeon Casl9#3 Name of Unclassified Species Taxonomy ID uncultured archaeon Casl9#4

uncultured archaeon Casl9#5

uncultured archaeon Casl9#6

uncultured archaeon Cas20#l

uncultured archaeon Cas20#2

uncultured archaeon Cas20#3

uncultured archaeon Cas20#4

uncultured archaeon Cas20#5

uncultured archaeon CR-PAlOa

uncultured archaeon CR-PA12a

uncultured archaeon CR-PA13a

uncultured archaeon CR-PAlSa

uncultured archaeon CR-PA16a

uncultured archaeon CR-PAIa

uncultured archaeon CR-PA2a

uncultured archaeon CR-PA4a

uncultured archaeon CR-PA6a

uncultured archaeon CR-PA7a

uncultured archaeon CR-PA8a

uncultured archaeon CRA12-27cm

uncultured archaeon CRA13-llcm

uncultured archaeon CRA20-0cm

uncultured archaeon CRA36-0cm

uncultured archaeon CRA4-23cm

uncultured archaeon CRA7-0cm

uncultured archaeon CRA7-llcm

uncultured archaeon CRA8-llcm

uncultured archaeon CRA8-23cm

uncultured archaeon CRA8-27cm

uncultured archaeon CRA9-27cm

uncultured archaeon CRE-FLlOa

uncultured archaeon CRE-FLlIa

uncultured archaeon CRE-FLIa

uncultured archaeon CRE-FL2a

uncultured archaeon CRE-FL3a

uncultured archaeon CRE-FL4a

uncultured archaeon CRE-FL5a

uncultured archaeon CRE-FL6a

uncultured archaeon CRE-FL7a

uncultured archaeon CRE-FL8a

uncultured archaeon CRE-FL9a

uncultured archaeon CRE-PAlOa

uncultured archaeon CRE-PAlIa

uncultured archaeon CRE-PA2a

uncultured archaeon CRE-PA3a

uncultured archaeon CRE-PA4a

uncultured archaeon CRE-PA5a

uncultured archaeon CRE-PA6a

uncultured archaeon CRE-PA7a

uncultured archaeon CRE-PA8a

uncultured archaeon CRE-PA9a

uncultured archaeon CRO-lla

uncultured archaeon CRO-12a

uncultured archaeon CRO-14a

uncultured archaeon CRO-Ia

uncultured archaeon CRO-2a

uncultured archaeon CRO-3a

uncultured archaeon CRO-4a

uncultured archaeon CRO-5a Name of Unclassified Species Taxonomy ID uncultured archaeon CRO-6a

uncultured archaeon CRO-7a

uncultured archaeon CRO-8a

uncultured archaeon DGGE band PSARC-I

uncultured archaeon DGGE band PSARC-2

uncultured archaeon EIb

uncultured archaeon ER-E

uncultured archaeon ER-H

uncultured archaeon GAOl

uncultured archaeon GA02

uncultured archaeon GA04

uncultured archaeon GAlO

uncultured archaeon GA32

uncultured archaeon GA42

uncultured archaeon GA54

uncultured archaeon GA55

uncultured archaeon GA67

uncultured archaeon GA77

uncultured archaeon GZfoslOC7

uncultured archaeon GZfosllAlO

uncultured archaeon GZfosllHll

uncultured archaeon GZfosl2El

uncultured archaeon GZfosl2E2

uncultured archaeon GZfosl3El

uncultured archaeon GZfosl4B8

uncultured archaeon GZfosl7A3

uncultured archaeon GZfosl7C7

uncultured archaeon GZfosl7Fl

uncultured archaeon GZfosl7Gll

uncultured archaeon GZfosl8B6

uncultured archaeon GZfosl8C8

uncultured archaeon GZfosl8F2

uncultured archaeon GZfoslδHll

uncultured archaeon GZfosl9A5

uncultured archaeon GZfosl9C7

uncultured archaeon GZfosl9C8

uncultured archaeon GZfoslCll

uncultured archaeon GZfoslDl

uncultured archaeon GZfos21B5

uncultured archaeon GZfos22D9

uncultured archaeon GZfos23H7

uncultured archaeon GZfos23H9

uncultured archaeon GZfos24D9

uncultured archaeon GZfos26B2

uncultured archaeon GZfos26D6

uncultured archaeon GZfos26D8

uncultured archaeon GZfos26E7

uncultured archaeon GZfos26F9

uncultured archaeon GZfos26G2

uncultured archaeon GZfos27A8

uncultured archaeon GZfos27B6

uncultured archaeon GZfos27E6

uncultured archaeon GZfos27E7

uncultured archaeon GZfos27G5

uncultured archaeon GZfos28B8

uncultured archaeon GZfos28G7

uncultured archaeon GZfos29E12

uncultured archaeon GZfos30H9

uncultured archaeon GZfos31B6 Name of Unclassified Species Taxonomy ID uncultured archaeon GZfos32E4

uncultured archaeon GZfos32E7

uncultured archaeon GZfos32G12

uncultured archaeon GZfos33El

uncultured archaeon GZfos33H6

uncultured archaeon GZfos34A6

uncultured archaeon GZfos34G5

uncultured archaeon GZfos34H10

uncultured archaeon GZfos34H9

uncultured archaeon GZfos35A2

uncultured archaeon GZfos35B7

uncultured archaeon GZfos35D7

uncultured archaeon GZfos36D8

uncultured archaeon GZfos37B2

uncultured archaeon GZfos37Dl

uncultured archaeon GZfos3D4

uncultured archaeon GZfos9C4

uncultured archaeon GZfos9Dl

uncultured archaeon GZfos9D8

uncultured archaeon GZfos9E5

uncultured archaeon HAOl

uncultured archaeon HA03

uncultured archaeon HA04

uncultured archaeon HA05

uncultured archaeon HA06

uncultured archaeon HA08

uncultured archaeon HA09

uncultured archaeon HAlO

uncultured archaeon HAIl

uncultured archaeon HA19

uncultured archaeon HA25

uncultured archaeon HA48

uncultured archaeon HA55

uncultured archaeon KNIAIl

uncultured archaeon KNIA12

uncultured archaeon KNIA13

uncultured archaeon KNIA14

uncultured archaeon KNIA15

uncultured archaeon nld

uncultured archaeon n41r

uncultured archaeon OS-I

uncultured archaeon OS-IO

uncultured archaeon OS-Il

uncultured archaeon OS-12

uncultured archaeon OS-13

uncultured archaeon OS-14

uncultured archaeon OS-15

uncultured archaeon OS-16

uncultured archaeon OS-17

uncultured archaeon OS-18

uncultured archaeon OS-19

uncultured archaeon OS-2

uncultured archaeon OS-20

uncultured archaeon OS-21

uncultured archaeon OS-22

uncultured archaeon OS-23

uncultured archaeon OS-24

uncultured archaeon OS-25

uncultured archaeon OS-26 Name of Unclassified Species Taxonomy ID uncultured archaeon OS-27

uncultured archaeon OS-28

uncultured archaeon OS-29

uncultured archaeon OS-3

uncultured archaeon OS-30

uncultured archaeon OS-31

uncultured archaeon OS-32

uncultured archaeon OS-33

uncultured archaeon OS-4

uncultured archaeon OS-5

uncultured archaeon OS-6

uncultured archaeon OS-7

uncultured archaeon OS-8

uncultured archaeon OS-9

uncultured archaeon pHGPAl

uncultured archaeon pHGPA13

uncultured archaeon pPACMA-A

uncultured archaeon pPACMA-B

uncultured archaeon pPACMA-C

uncultured archaeon pPACMA-E

uncultured archaeon pPACMA-F

uncultured archaeon pPACMA-G

uncultured archaeon pPACMA-H

uncultured archaeon pPACMA-I

uncultured archaeon pPACMA-J

uncultured archaeon pPACMA-K

uncultured archaeon pPACMA-L

uncultured archaeon pPACMA-M

uncultured archaeon pPACMA-N

uncultured archaeon pPACMA-P

uncultured archaeon pPACMA-Q

uncultured archaeon pPACMA-S

uncultured archaeon pPACMA-T

uncultured archaeon pPACMA-U

uncultured archaeon pPACMA-V

uncultured archaeon pPACMA-W

uncultured archaeon pPACMA-X

uncultured archaeon pPACMA-Y

uncultured archaeon pPCAlO.l

uncultured archaeon pPCA12.14

uncultured archaeon pPCA12.6

uncultured archaeon pPCA13.4

uncultured archaeon pPCA13.5

uncultured archaeon pPCA14.16

uncultured archaeon pPCA14.17

uncultured archaeon pPCA14.18

uncultured archaeon pPCA14.41

uncultured archaeon pPCA15.21

uncultured archaeon pPCA17.1

uncultured archaeon pPCA19.6

uncultured archaeon pPCA2.4

uncultured archaeon pPCA4.21

uncultured archaeon pPCA4.4

uncultured archaeon pPCA4.9

uncultured archaeon pPCA7.13

uncultured archaeon pPCA7.17

uncultured archaeon pPCA7.21

uncultured archaeon pPCA7.30

uncultured archaeon pPCA7.34 Name of Unclassified Species Taxonomy ID uncultured archaeon pPCA7.6

uncultured archaeon pPCA7.8

uncultured archaeon pPCA8.3

uncultured archaeon RSS50-1

uncultured archaeon RSS50-10

uncultured archaeon RSS50-11

uncultured archaeon RSS50-2

uncultured archaeon RSS50-3

uncultured archaeon RSS50-4

uncultured archaeon RSS50-5

uncultured archaeon RSS50-6

uncultured archaeon RSS50-7

uncultured archaeon RSS50-8

uncultured archaeon RSS50-9

uncultured archaeon S15-1

uncultured archaeon S15-10

uncultured archaeon S15-11

uncultured archaeon S15-12

uncultured archaeon S15-13

uncultured archaeon S15-14

uncultured archaeon S15-15

uncultured archaeon S15-16

uncultured archaeon S15-17

uncultured archaeon S15-18

uncultured archaeon S15-19

uncultured archaeon S15-2

uncultured archaeon S15-20

uncultured archaeon S15-21

uncultured archaeon S15-22

uncultured archaeon S15-23

uncultured archaeon S15-24

uncultured archaeon S15-25

uncultured archaeon S15-26

uncultured archaeon S15-27

uncultured archaeon S15-28

uncultured archaeon S15-29

uncultured archaeon S15-3

uncultured archaeon S15-30

uncultured archaeon S15-4

uncultured archaeon S15-5

uncultured archaeon S15-6

uncultured archaeon S15-7

uncultured archaeon S15-8

uncultured archaeon S15-9

uncultured archaeon S30-1

uncultured archaeon S30-10

uncultured archaeon S30-11

uncultured archaeon S30-12

uncultured archaeon S30-13

uncultured archaeon S30-14

uncultured archaeon S30-15

uncultured archaeon S30-16

uncultured archaeon S30-17

uncultured archaeon S30-18

uncultured archaeon S30-19

uncultured archaeon S30-2

uncultured archaeon S30-20

uncultured archaeon S30-21

uncultured archaeon S30-22 Name of Unclassified Species Taxonomy ID uncultured archaeon S30-23

uncultured archaeon S30-24

uncultured archaeon S30-25

uncultured archaeon S30-26

uncultured archaeon S30-27

uncultured archaeon S30-28

uncultured archaeon S30-29

uncultured archaeon S30-3

uncultured archaeon S30-30

uncultured archaeon S30-4

uncultured archaeon S30-5

uncultured archaeon S30-6

uncultured archaeon S30-7

uncultured archaeon S30-8

uncultured archaeon S30-9

uncultured archaeon SAGMA-I

uncultured archaeon SAGMA-10

uncultured archaeon SAGMA-Il

uncultured archaeon SAGMA-12

uncultured archaeon SAGMA-13

uncultured archaeon SAGMA-14

uncultured archaeon SAGMA-15

uncultured archaeon SAGMA-16

uncultured archaeon SAGMA-17

uncultured archaeon SAGMA-2

uncultured archaeon SAGMA-3

uncultured archaeon SAGMA-4

uncultured archaeon SAGMA-6

uncultured archaeon SAGMA-7

uncultured archaeon SAGMA-8

uncultured archaeon SAGMA-9

uncultured archaeon SAGMA-A

uncultured archaeon SAGMA-B

uncultured archaeon SAGMA-C

uncultured archaeon SAGMA-D

uncultured archaeon SAGMA-E

uncultured archaeon SAGMA-F

uncultured archaeon SAGMA-G

uncultured archaeon SAGMA-H

uncultured archaeon SAGMA-I

uncultured archaeon SAGMA-J

uncultured archaeon SAGMA-J2

uncultured archaeon SAGMA-K

uncultured archaeon SAGMA-L

uncultured archaeon SAGMA-M

uncultured archaeon SAGMA-N

uncultured archaeon SAGMA-O

uncultured archaeon SAGMA-P

uncultured archaeon SAGMA-Q

uncultured archaeon SAGMA-R

uncultured archaeon SAGMA-S

uncultured archaeon SAGMA-T

uncultured archaeon SAGMA-U

uncultured archaeon SAGMA-V

uncultured archaeon SAGMA-W

uncultured archaeon SAGMA-X

uncultured archaeon SAGMA-Y

uncultured archaeon SAGMA-Z

uncultured archaeon SCl Name of Unclassified Species Taxonomy ID uncultured archaeon SC2

uncultured archaeon SC4

uncultured archaeon SC6

uncultured archaeon SC7

uncultured archaeon SJC-l lb

uncultured archaeon SJC-125a

uncultured archaeon SJD-102

uncultured archaeon SJD-103

uncultured archaeon SJD-105

uncultured archaeon SJD-107

uncultured archaeon SJD-111

uncultured archaeon SJD-114

uncultured archaeon SL-C

uncultured archaeon SLl-I

uncultured archaeon SL2-d

uncultured archaeon SMl

uncultured archaeon SM1K20

uncultured archaeon STl-I

uncultured archaeon STl-IO

uncultured archaeon STl-Il

uncultured archaeon ST1-12

uncultured archaeon ST1-13

uncultured archaeon ST1-14

uncultured archaeon ST1-15

uncultured archaeon ST1-16

uncultured archaeon ST1-17

uncultured archaeon ST1-18

uncultured archaeon ST1-19

uncultured archaeon ST1-2

uncultured archaeon ST1-20

uncultured archaeon ST1-21

uncultured archaeon ST1-22

uncultured archaeon ST1-23

uncultured archaeon ST1-24

uncultured archaeon ST1-25

uncultured archaeon ST1-26

uncultured archaeon ST1-27

uncultured archaeon ST1-28

uncultured archaeon ST1-29

uncultured archaeon ST1-3

uncultured archaeon ST1-30

uncultured archaeon ST1-4

uncultured archaeon ST1-5

uncultured archaeon ST1-6

uncultured archaeon ST1-7

uncultured archaeon ST1-8

uncultured archaeon ST1-9

uncultured archaeon SWl

uncultured archaeon SW14

uncultured archaeon SW3

uncultured archaeon SW9

uncultured archaeon SWY

uncultured archaeon SYA-I

uncultured archaeon SYA-106

uncultured archaeon SYA-112

uncultured archaeon SYA-12

uncultured archaeon SYA-122

uncultured archaeon SYA-125

uncultured archaeon SYA-127

- Ill - Name of Unclassified Species Taxonomy ID uncultured archaeon SYA-13

uncultured archaeon SYA-130

uncultured archaeon SYA-133

uncultured archaeon SYA-136

uncultured archaeon SYA-141

uncultured archaeon SYA-20

uncultured archaeon SYA-26

uncultured archaeon SYA-30

uncultured archaeon SYA-32

uncultured archaeon SYA-39

uncultured archaeon SYA-45

uncultured archaeon SYA-5

uncultured archaeon SYA-50

uncultured archaeon SYA-62

uncultured archaeon SYA-7

uncultured archaeon SYA-70

uncultured archaeon SYA-74

uncultured archaeon SYA-75

uncultured archaeon SYA-77

uncultured archaeon SYA-78

uncultured archaeon SYA-8

uncultured archaeon SYA-80

uncultured archaeon SYA-81

uncultured archaeon SYA-94

uncultured archaeon SYA_2000 10

uncultured archaeon SYA_2000_ll

uncultured archaeon SYA_2000_12

uncultured archaeon SYA_2000_13

uncultured archaeon SYA_2000 14

uncultured archaeon SYA_2000 15

uncultured archaeon SYA_2000 16

uncultured archaeon SYA_2000_17

uncultured archaeon SYA_2000_18

uncultured archaeon SYA_2000_19

uncultured archaeon SYA_2000 2

uncultured archaeon SYA_2000 20

uncultured archaeon SYA_2000 21

uncultured archaeon SYA_2000_24

uncultured archaeon SYA_2000_26

uncultured archaeon SYA_2000_27

uncultured archaeon SYA_2000 28

uncultured archaeon SYA_2000 30

uncultured archaeon SYA_2000_31

uncultured archaeon SYA_2000_32

uncultured archaeon SYA_2000_35

uncultured archaeon SYA_2000 36

uncultured archaeon SYA_2000 37

uncultured archaeon SYA_2000 39

uncultured archaeon SYA_2000_40

uncultured archaeon SYA_2000_41

uncultured archaeon SYA_2000_43

uncultured archaeon SYA_2000 44

uncultured archaeon SYA_2000 45

uncultured archaeon SYA_2000 46

uncultured archaeon SYA_2000_47

uncultured archaeon SYA_2000_5

uncultured archaeon SYA_2000_51

uncultured archaeon SYA_2000 52

uncultured archaeon SYA_2000_54 Name of Unclassified Species Taxonomy ID uncultured archaeon SYA_2000 55

uncultured archaeon SYA_2000 57

uncultured archaeon SYA_2000_58

uncultured archaeon SYA_2000_59

uncultured archaeon SYA_2000_6

uncultured archaeon SYA_2000 60

uncultured archaeon SYA_2000 61

uncultured archaeon SYA_2000_62

uncultured archaeon SYA_2000_63

uncultured archaeon SYA_2000_66

uncultured archaeon SYA_2000 67

uncultured archaeon SYA_2000 68

uncultured archaeon SYA_2000 7

uncultured archaeon SYA_2000_70

uncultured archaeon SYA_2000_8

uncultured archaeon SYA_2000_9

uncultured archaeon TAOl

uncultured archaeon TA02

uncultured archaeon TA03

uncultured archaeon TA04

uncultured archaeon TA05

uncultured archaeon VC2.1 Arcl

uncultured archaeon VC2.1 Arcl3

uncultured archaeon VC2.1 Arcl6

uncultured archaeon VC2.1 Arc2

uncultured archaeon VC2.1 Arc31

uncultured archaeon VC2.1 Arc35

uncultured archaeon VC2.1 Arc36

uncultured archaeon VC2.1 Arc4

uncultured archaeon VC2.1 Arc5

uncultured archaeon VC2.1 Arc6

uncultured archaeon VC2.1 Arc7

uncultured archaeon VC2.1 Arc8

uncultured archaeon WSB-I

uncultured archaeon WSB-10

uncultured archaeon WSB-Il

uncultured archaeon WSB-12

uncultured archaeon WSB-13

uncultured archaeon WSB-14

uncultured archaeon WSB-15

uncultured archaeon WSB-16

uncultured archaeon WSB-17

uncultured archaeon WSB-18

uncultured archaeon WSB-19

uncultured archaeon WSB-2

uncultured archaeon WSB-20

uncultured archaeon WSB-21

uncultured archaeon WSB-3

uncultured archaeon WSB-4

uncultured archaeon WSB-5

uncultured archaeon WSB-6

uncultured archaeon WSB-7

uncultured archaeon WSB-8

uncultured archaeon WSB-9

uncultured archeon 'KTK 18A'

uncultured archeon 'KTK 28A'

uncultured archeon 'KTK 31A'

uncultured archeon 'KTK 4A'

uncultured archeon 'KTK 9A' Name of Unclassified Species Taxonomy ID uncultured Baπisveld landfill archaeon BVIowarchb2

uncultured Banisveld landfill archaeon BVupparchbl

uncultured compost archaeon

uncultured deep-sea archaeon

uncultured endolithic archaeon

uncultured equine intestinal archaeal sp. DLIl

uncultured maize rhizosphere archaeon c9_45(Cr)

uncultured maize root archaeon ZmrAl

uncultured maize root archaeon ZmrA19

uncultured maize root archaeon ZmrA30

uncultured maize root archaeon ZmrA38

uncultured maize root archaeon ZmrA4

uncultured maize root archaeon ZmrA42

uncultured marine archaeon

uncultured marine archaeon DCM3921

uncultured marine archaeon DCM6515

uncultured marine archaeon DCM65231

uncultured marine archaeon DCM74159

uncultured marine archaeon DCM74161

uncultured marine archaeon DCM858

uncultured marine archaeon DCM860

uncultured marine archaeon DCM861

uncultured marine archaeon DCM862

uncultured marine archaeon DCM863

uncultured marine archaeon DCM865

uncultured marine archaeon DCM866

uncultured marine archaeon DCM867

uncultured marine archaeon DCM871

uncultured marine archaeon DCM873

uncultured marine archaeon DCM874

uncultured marine archaeon DCM875

uncultured marine archaeon FF619

uncultured marine archaeon FF620

uncultured marine archaeon FIN625

uncultured marine archaeon FIN654

uncultured marine archaeon GIN492

uncultured marine archaeon TS10C286

uncultured marine archaeon TS10C294

uncultured marine archaeon TS10C298

uncultured marine archaeon TS10C299

uncultured marine archaeon TS235C302

uncultured marine archaeon TS235C306

uncultured marine archaeon TS235C310

uncultured methane-oxidizing archaeon

uncultured methanogen R5

uncultured methanogen R8

uncultured methanogen R9

uncultured rumen archaeon

uncultured rumen archaeon Ml

uncultured rumen archaeon M2

uncultured rumen archaeon M7

uncultured rumen methanogen

uncultured rumen methanogen 15

uncultured rumen methanogen 2

uncultured rumen methanogen 956

uncultured rumen methanogen Hole9

uncultured rumen methanogen M6

uncultured soil archaeon

uncultured sponge symbiont PAAR2 Name of Unclassified Species J Taxonomy ID uncultured sponge symbiont PAAR4

uncultured sponge symbiont PAAR8

uncultured sponge symbiont PAAR9

uncultured thermal soil archaeon

uncultured vent archaeon

unidentified archaeon

unidentified archaeon Hl-Bl

unidentified archaeon H1-K16

unidentified archaeon H1-K19

unidentified archaeon H1-K2

unidentified archaeon H1-K9

unidentified archaeon H6-B1

unidentified archaeon H6-K5

unidentified archaeon H6-K6

unidentified archaeon HB3-1

unidentified archaeon S3-K14

unidentified archaeon S3-K15

unidentified archaeon S3-K25

unidentified archaeon S3-K5

unidentified archaeon S3-K9

unidentified hydrothermal vent archaeon PVA_OTU_1

unidentified hydrothermal vent archaeon PVA_OTU_3

unidentified marine archaeon p712-12

unidentified marine archaeon p712-13

unidentified marine archaeon p712-24

unidentified marine archaeon p712-3

unidentified marine archaeon p712-37

unidentified marine archaeon p712-63

TABLE 4

TABLE 5

Claims

What is claimed is:

1. A system to convert electric power into methane, the system comprising: a biological reactor having at least a first chamber containing at least a cathode, a culture comprising methanogenic microorganisms, and water, and a second chamber containing at least an anode,

the biological reactor having an operating state wherein the culture is maintained at a temperature above 50 ⁰C;

a source of electricity coupled to the anode and the cathode;

a supply of carbon dioxide coupled to the first chamber; and

an outlet to receive methane from the first chamber.

2. The system of claim 1, wherein the reactor has an operating state wherein the culture is maintained in the first chamber at a temperature of about 55° C or higher.

3. The system of claim 2, wherein the reactor has an operating state wherein the culture is maintained in the first chamber at a temperature of about 60 ° C or higher.

4. The system according to claim 1, further comprising a proton permeable, at least gas semipermeable barrier separating the first and second chambers.

5. The system according to claim 4, wherein the barrier comprises a solid polymer electrolyte membrane.

6 The system according to claim 1, wherein the cathode comprises a porous electrically conductive material.

7 The system according to claim 6, wherein the porous electrically conductive material comprises a reticulated carbon foam.

8 The system according to claim 7, wherein the methanogenic microorganisms are impregnated into the reticulated carbon foam.

9 The system according to claim 1, wherein the culture comprises Archaea adapted to nearly stationary growth conditions.

10. The system according to claim 1, wherein the culture comprises Archaea of the subkingdom Euryarcheaota.

11. The system according to claim 10, wherein the culture is a monoculture of Euryarcheaota.

12. The system according to claim 11, wherein the Archaea consist essentially of Methanothermobacter thermautotrophicus .

13. The system according to claim 1, wherein the biological reactor has the operating state and a dormant state, the reactor changing from the dormant state to the operating state without addition of methanogenic microorganisms.

14. The system according to claim 13, wherein the dormant state exists when the biological reactor is decoupled from the source of electricity or the source of carbon dioxide.

15. The system according to claim 1, wherein the source of electricity comprises at least one of a coal-fired power plant, a natural-gas fired power plant, a biomass-fired power plant, a nuclear power plant, a wind-powered turbine, a water-powered turbine, a fuel cell, a geothermal power source, a solar thermal system or a photovoltaic system.

16. The system according to claim 1, wherein oxygen is the only gaseous byproduct.

17. The system according to claim 1, wherein water is a primary net electron donor for the methanogenic microorganisms.

18. The system according to claim 1, wherein the biological reactor operates at an electrical current density above 6 mA/cm².

19. A method of converting electricity into methane, the method comprising: supplying electricity to an anode and a cathode of biological reactor having at least a first chamber containing at least the cathode, a culture comprising methanogenic

microorganisms, and water, and a second chamber containing at least the anode, the biological reactor having an operating state, wherein the culture is maintained at a temperature above 50⁰C;

supplying carbon dioxide to the first chamber; and

collecting methane from the first chamber.

20. The method of claim 19, further comprising generating electricity from carbon-free, renewable sources.

21. The method of claim 20, wherein generating electricity from carbon-free, renewable sources comprises generating electricity from wind, water, geothermal and solar sources.

22. The method of any one of claims 19-21, wherein supplying electricity comprises supplying electricity during a non-peak demand period.

23. The method of claim 19, further comprising collecting oxygen from the second chamber.

24. The method of claim 19, further comprising storing and transporting the methane.

25. The method of claim 19, wherein supplying carbon dioxide comprises recycling carbon dioxide from at least a concentrated industrial source or atmospheric carbon dioxide.

26. A method of creating carbon credits, the method comprising:

supplying electricity to an anode and a cathode of biological reactor having at least a first chamber containing at least the cathode, a culture comprising methanogenic

microorganisms, and water, and a second chamber containing at least the anode, the biological reactor having an operating state wherein the culture is maintained at a temperature about 50 ⁰C;

supplying carbon dioxide to the first chamber; and

receiving carbon credits for the carbon dioxide converted in the biological reactor into methane.

27. The method of claim 26, wherein supplying carbon dioxide comprises recycling carbon dioxide from a concentrated industrial source.

28. A biological process for producing methane gas comprising:

providing an electromethanogenic reactor having an anode, a cathode, and a plurality of methanogenic microorganisms disposed on the cathode;

providing electrons to the plurality of methanogenic microorganisms disposed on the cathode; and

providing carbon dioxide to the plurality of methanogenic microorganisms, whereby the methanogenic microorganisms reduce the carbon dioxide to produce methane gas.

29. The process of claim 28, wherein a power source is in electrical

communication with the reactor to enhance a potential between the anode and the cathode.

30. The process of claim 29, wherein the power source is selected from the group consisting of: wind-generated power, solar power, a microbial fuel cell, a DC power source, an electrochemical cell, and a combination of two or more thereof.

31. The process of claim 28, further comprising increasing methane gas production rate by adding an additional voltage to the cathode.

32. The process of claim 28, wherein the electromethanogenic reactor comprises an anode chamber and a cathode chamber.

33. The process of claim 32, wherein no organic carbon source is added to the cathode chamber.

34. The process of claim 28, wherein no hydrogen is added to the cathode chamber.

35. The process of claim 28, wherein substantially no organic carbon source is available to the plurality of methanogenic microorganisms,

36. The process of claim 28, wherein metal catalysts are substantially excluded from the cathode.

37. A biological process for producing methane gas, comprising:

inserting an anode and a cathode in a methanogenic reactor comprising methanogenic microorganisms; and

providing electrons to the methanogenic microorganisms, increasing the efficiency of the methanogenic reactor to produce methane gas.

38. The process of claim 37, wherein providing electrons comprises applying a voltage to the cathode.

39. The process of claim 38, wherein the voltage is generated by a power source selected from the group consisting of: wind-generated power, solar power, a microbial fuel cell, a DC power source, an electrochemical cell, and a combination of two or more thereof.

40. An electromethanogenic reactor, comprising:

an anode; and

a cathode comprising methanogenic microorganisms.

41. The electromethanogenic reactor of claim 40, further comprising a power source in electrical communication with the reactor to add a voltage to the cathode.