Classifications

• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/64—Fats; Fatty oils; Ester-type waxes; Higher fatty acids, i.e. having at least seven carbon atoms in an unbroken chain bound to a carboxyl group; Oxidised oils or fats
  • C12P7/6436—Fatty acid esters
  • C12P7/649—Biodiesel, i.e. fatty acid alkyl esters
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
  • C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
  • C12N9/14—Hydrolases (3)
  • C12N9/16—Hydrolases (3) acting on ester bonds (3.1)
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/64—Fats; Fatty oils; Ester-type waxes; Higher fatty acids, i.e. having at least seven carbon atoms in an unbroken chain bound to a carboxyl group; Oxidised oils or fats
  • C12P7/6409—Fatty acids
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E50/00—Technologies for the production of fuel of non-fossil origin
  • Y02E50/10—Biofuels, e.g. bio-diesel
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/50—Improvements relating to the production of bulk chemicals
  • Y02P20/582—Recycling of unreacted starting or intermediate materials
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T50/00—Aeronautics or air transport
  • Y02T50/60—Efficient propulsion technologies, e.g. for aircraft
  • Y02T50/678—Aviation using fuels of non-fossil origin

Definitions

• This invention relates to photosynthetic microorganisms that convert inorganic carbon to fatty acids and secrete them into the culture medium, methods of production of fatty acids using such organisms, and uses thereof.
• the fatty acids may be used directly or may be further modified to alternate forms such as esters, reduced forms such as alcohols, or hydrocarbons, for applications in different industries, including fuels and chemicals.
• Photosynthetic microorganisms including eukaryotic algae and cyanobacteria, contain various lipids, including polar lipids and neutral lipids.
• Polar lipids e.g., phospholipids, glycolipids, sulfolipids
• neutral lipids e.g., triacylglycerols, wax esters
• a substantial research effort has been devoted to the development of methods to produce lipid-based fuels and chemicals from photosynthetic microorganisms.
• eukaryotic microalgae are grown under nutrient-replete conditions until a certain cell density is achieved, after which the cells are subjected to growth under nutrient- deficient conditions, which often leads to the accumulation of neutral lipids.
• the cells are then harvested by various means (e.g., settling, which can be facilitated by the addition of flocculants, followed by centrifugation), dried, and then the lipids are extracted from the cells by the use of various non-polar solvents.
• Harvesting of the cells and extraction of the lipids are cost-intensive steps. It would be desirable to obtain lipids from photosynthetic microorganisms without the requirement for cell harvesting and extraction.
• PCT publication numbers WO2007/136762 and WO2008/119082 describe the production of biofuel components using microorganisms. These documents disclose the production by these organisms of fatty acid derivatives which are, apparently, short and long chain alcohols, hydrocarbons, fatty alcohols and esters including waxes, fatty acid esters or fatty esters. To the extent that fatty acid production is described, it is proposed as an intermediate to these derivatives, and the fatty acids are therefore not secreted. Further, there is no disclosure of converting inorganic carbon directly to secreted fatty acids using a photosynthetic organism grown in a culture medium containing inorganic carbon as the primary carbon source. The present invention takes advantage of the efficiency of photosynthetic organisms in secreting fatty acids into the medium in order to recover these valuable compounds.
• the invention includes the expression of heterologous acyl-ACP thioesterase (TE) genes in photosynthetic microbes. Many of these genes, along with their use to alter lipid metabolism in oilseeds, have been described previously. Genes encoding the proteins that catalyze various steps in the synthesis and further metabolism of fatty acids have also been extensively described.
• TE heterologous acyl-ACP thioesterase
• fatty acid synthetase catalyzes a repeating cycle wherein malonyl-acyl carrier protein (ACP) is condensed with a substrate, initially acetyl-CoA, to form acetoacetyl-ACP, liberating CO 2 .
• ACP malonyl-acyl carrier protein
• the acetoacetyl-ACP is then reduced, dehydrated, and reduced further to butyryl-ACP which can then itself be condensed with malonyl-ACP, and the cycle repeated, adding a 2-carbon unit at each turn.
• the production of free fatty acids would therefore be enhanced by a thioesterase that would liberate the fatty acid itself from ACP, breaking the cycle.
• the acyl-ACP is prevented from reentering the cycle. Production of the fatty acid would also be encouraged by enhancing the levels of fatty acid synthetase and inhibiting any enzymes which result in degradation or further metabolism of the fatty acid.
• Figure 2 presents a more detailed description of the sequential formation of acyl- ACPs of longer and longer chains. As shown, the thioesterase enzymes listed in Figure 2 liberate the fatty acid from the ACP thioester.
• Voelker, T., and Davies, M., Journal of Bacteriology (1994) 176:7320-7327 ' describe "Alteration of the specificity and regulation of fatty acid synthesis of Escherichia coli by expression of a plant medium-chain acyl-acyl carrier protein thioesterase.”
• the present invention is directed to the production of recombinant photosynthetic microorganisms that are able to secrete fatty acids derived from inorganic carbon into the culture medium. Methods to remove the secreted fatty acids from the culture medium without the need for cell harvesting are also provided. It is anticipated that these improvements will lead to lower costs for producing lipid-based fuels and chemicals from photosynthetic microorganisms. In addition, this invention enables the production of fatty acids of defined chain length, thus allowing their use in the formulation of a variety of different products, including fuels and chemicals.
• Carbon dioxide (which, along with carbonic acid, bicarbonate and/or carbonate define the term "inorganic carbon") is converted in the photosynthetic process to organic compounds.
• the inorganic carbon source includes any way of delivering inorganic carbon, optionally in admixture with any other combination of compounds which do not serve as the primary carbon feedstock, but only as a mixture or carrier (for example, emissions from biofuel (e.g., ethanol) plants, power plants, petroleum-based refineries, as well as atmospheric and subterranean sources).
• biofuel e.g., ethanol
• One embodiment of the invention relates to a culture of recombinant photosynthetic microorganisms, said organisms comprising at least one recombinant expression vector encoding at least one exogenous acyl- ACP thioesterase, wherein the at least one exogenous acyl- ACP thioesterase preferentially liberates fatty acid chains containing 6 to 20 carbons from these ACP thioesters.
• the fatty acids are formed from inorganic carbon as their carbon source and the culture contains substantially only inorganic carbon as a carbon source. The presence of the exogenous thioesterase will increase the secretion levels of desired fatty acids by at least 2-4 fold.
• the invention is directed to a cell culture of a recombinant photo synthetic microorganism where the microorganism has been modified to contain a nucleic acid molecule comprising at least one recombinant expression system that produces at least one exogenous acyl-ACP thioesterase, wherein said acyl-ACP thioesterase preferentially liberates a fatty acid chain that contains 6-20 carbons, and wherein the culture medium provides inorganic carbon as substantially the sole carbon source and wherein said microorganism secretes the fatty acid liberated by the acyl- ACP thioesterase into the medium.
• the thioesterase preferentially liberates a fatty acid chain that contains 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbons.
• the invention is directed to a method to produce fatty acids of desired chain lengths by incubating these cultures and recovering these secreted fatty acids from the cultures.
• the recovery employs solid particulate adsorbents to harvest the secreted fatty acids.
• the fatty acids thus recovered can be further modified synthetically or used directly as components of biofuels or chemicals.
• Figure 1 is a diagram of the pathway of fatty acid synthesis as is known in the art.
• Figure 2 is a more detailed diagram of the synthesis of fatty acids of multiple chain lengths as is known in the art.
• Figure 3 is an enzymatic overview of fatty acid biosynthesis identifying enzymatic classes for the production of various chain length fatty acids.
• Figure 4 is a schematic diagram of a recovery system for fatty acids from the medium.
• Figure 5 shows an experimental system based on the principles in Figure 4.
• Figure 6 shows representative acyl-ACP thioesterase from a variety of organisms.
• the present invention provides photosynthetic microorganisms that secrete fatty acids into the culture medium, along with methods to adsorb the fatty acids from the culture medium and collect them for processing into fuels and chemicals.
• the invention thereby eliminates or greatly reduces the need to harvest and extract the cells, resulting in substantially reduced production costs.
• FIG. 2 is an overview of one aspect of the invention.
• carbon dioxide is converted to acetyl-CoA using the multiple steps in the photosynthetic process.
• the acetyl-CoA is then converted to malonyl-CoA by the action of acetyl-CoA carboxylase.
• the malonyl-CoA is then converted to malonyl-ACP by the action of malonyl- CoA:ACP transacylase which, upon progressive action of fatty acid synthetase, results in successive additions of two carbon units.
• the process is essentially halted at carbon chain lengths of 6 or 8 or 10 or 12 or 14 or 16 or 18 carbons by supplying the appropriate thioesterase (shown in Figure 2 as FatB).
• FatB thioesterase
• the cell biomass can be harvested as well.
• the secreted fatty acids can be converted to various other forms including, for example, methyl esters, alkanes, alkenes, alpha-olefins and fatty alcohols.
• the organism In order to effect secretion of the free fatty acids, the organism is provided at least one expression system for at least one thioesterase that operates preferentially to liberate fatty acids of the desired length.
• thioesterase that operates preferentially to liberate fatty acids of the desired length.
• Examples include U.S. Patent 5298421, entitled “Plant medium-chain-preferring acyl-ACP thioesterases and related methods," which describes the isolation of an acyl-ACP thioesterase and the gene that encodes it from the immature seeds of Umbellularia calif ornica.
• Other sources for such thioesterases and their encoding genes include U.S. Patent 5,304,481, entitled “Plant thioesterase having preferential hydrolase activity toward C12 acyl-ACP substrate," U.S. Patent 5,344,771, entitled “Plant thioesterases," U.S. Patent 5,455,167, entitled “Medium-chain thioesterases in plants,” U.S.
• Patent 5,512,482 entitled “Plant thioesterases”
• U.S. Patent 5,530,186 entitled “Nucleotide sequences of soybean acyl-ACP thioesterase genes”
• U.S. Patent 5,639,790 entitled “Plant medium-chain thioesterases”
• U.S. Patent 5,667 ',997 ' entitled “C8 and ClO medium-chain thioesterases in plants
• U.S. Patent 5,723,761 entitled “Plant acyl-ACP thioesterase sequences”
• U.S. Patent 5,807,893 entitled “Plant thioesterases and use for modification of fatty acid composition in plant seed oils”
• Patent 5,850,022 entitled “Production of myristate in plant cells”
• U.S. Patent 5,910,631 entitled “Middle chain- specific thioesterase genes from Cuphea lanceolata”
• U.S. Patent 5,955,329 entitled “Engineering plant thioesterases for altered substrate specificity”
• Patent 5,955,650 entitled “Nucleotide sequences of canola and soybean palmitoyl-ACP thioesterase genes and their use in the regulation of fatty acid content of the oils of soybean and canola plants," and U.S. Patent 6,331,664, entitled “Acyl-ACP thioesterase nucleic acids from maize and methods of altering palmitic acid levels in transgenic plants therewith.”
• acyl-ACP TEs can be isolated from plants that naturally contain large amounts of medium-chain fatty acids in their seed oil, including certain plants in the Lauraceae, Lythraceae, Rutaceae, Ulmaceae, and Vochysiaceae families.
• the fatty acids produced by the seeds of these plants are esterified to glycerol and retained inside the cells. The seeds containing the products can then be harvested and processed to isolate the fatty acids.
• Other sources of these enzymes, such as bacteria may also be used.
• the known acyl-ACP TEs from plants can be divided into two main classes, based on their amino acid sequences and their specificity for acyl-ACPs of differing chain lengths and degrees of unsaturation.
• the "FatA” type of plant acyl-ACP TE has preferential activity on oleoyl-ACP, thereby releasing oleic acid, an 18-carbon fatty acid with a single double bond nine carbons distal to the carboxyl group.
• the "FatB" type of plant acyl-ACP TE has preferential activity on saturated acyl-ACPs, and can have broad or narrow chain length specificities.
• FatB enzymes from different species of Cuphea have been shown to release fatty acids ranging from eight carbons in length to sixteen carbons in length from the corresponding acyl-ACPs.
• fatty acids ranging from eight carbons in length to sixteen carbons in length from the corresponding acyl-ACPs.
• Table 1 Listed below in Table 1 are several plant acyl- ACP TEs along with their substrate preferences. (Fatty acids are designated by standard shorthand notation, wherein the number preceding the colon represents the acyl chain length and the number after the colon represents the number of double bonds in the acyl chain.)
• acyl- ACP TEs are exemplary and many additional genes encoding acyl- ACP TEs can be isolated and used in this invention, including but not limited to genes such as those that encode the following acyl- ACP TEs (referred to by GenPept Accession Numbers):
• acyl-ACP TEs include: Arabidopsis thaliana (At); Bradyrhizobium japonicum (Bj); Brassica napus (Bn); Cinnamonum camphorum (Cc); Capsicum chinense (Cch); Cuphea hookeriana (Ch); Cuphea lanceolata (Cl); Cuphea palustris (Cp); Coriandrum sativum (Cs); Carthamus tinctorius (Ct); Cuphea wrightii (Cw); Elaeis guineensis (Eg); Gossypium hirsutum (Gh); Garcinia mangostana (Gm); Helianthus annuus (Ha); Iris germanica (Ig); Iris tectorum (It); Myristica fragrans (Mf); Triticum aestivum (Ta); Ulmus Americana (Ua); and Umbellularia calif or
• the present invention contemplates the specific production of an individual length of medium-chain fatty acid, for example, predominently producing C8 fatty acids in one culture of recombinant photosynthetic microorganisms.
• the present invention contemplates the production of a combination of two or more different length fatty acids, for example, both C8 and ClO fatty acids in one culture of recombinant photosynthetic microorganisms.
• the host may be modified to include an expression system for a heterologous gene that encodes a ⁇ -ketoacyl synthase (KAS) that preferentially produces acyl-ACPs having medium chain lengths.
• KAS ⁇ -ketoacyl synthase
• Such KAS enzymes have been described from several plants, including various species of Cuphea. See Dehesh, K., et al, The Plant Journal (1998) 15:383-390, describe "KAS IV: a 3-ketoacyl-ACP synthase from Cuphea sp.
• the photosynthetic host cell containing a heterologous acyl-ACP TE gene may be further modified to include an expression system for a heterologous gene that encodes a multifunctional acetyl-CoA carboxylase or a set of heterologous genes that encode the various subunits of a multi-subunit type of acetyl-CoA carboxylase.
• heterologous genes that encode additional enzymes or components of the fatty acid biosynthesis pathway could also be introduced and expressed in acyl-ACP TE-containing host cells.
• the photosynthetic microorganism may also be modified such that one or more genes that encode beta-oxidation pathway enzymes have been inactivated or downregulated, or the enzymes themselves may be inhibited. This would prevent the degradation of fatty acids released from acyl-ACPs, thus enhancing the yield of secreted fatty acids.
• the desired products are medium-chain fatty acids
• the inactivation or downregulation of genes that encode acyl-CoA synthetase and/or acyl-CoA oxidase enzymes that preferentially use these chain lengths as substrates would be beneficial.
• Mutations in the genes encoding medium-chain-specific acyl-CoA synthetase and/or medium-chain-specific acyl-CoA oxidase enzymes such that the activity of the enzymes is diminished would also be effective in increasing the yield of secreted fatty acids.
• An additional modification inactivates or down-regulates the acyl-ACP synthetase gene or inactivates the gene or protein.
• Mutations in the genes can be introduced either by recombinant or non-recombinant methods. These enzymes and their genes are well known, and may be targeted specifically by disruption, deletion, generation of antisense sequences, generation of ribozymes or other recombinant approaches known to the practitioner. Inactivation of the genes can also be accomplished by random mutation techniques such as UV, and the resulting cells screened for successful mutants.
• the proteins themselves can be inhibited by intracellular generation of appropriate antibodies or intracellular generation of peptide inhibitors.
• the photosynthetic microorganism may also be modified such that one or more genes that encode storage carbohydrate or polyhydroxyalkanoate (PHA) biosynthesis pathway enzymes have been inactivated or down-regulated, or the enzymes themselves may be inhibited.
• PHA polyhydroxyalkanoate
• Examples include enzymes involved in glycogen, starch, or chrysolaminarin synthesis, including glucan synthases and branching enzymes.
• Other examples include enzymes involved in PHA biosynthesis such as acetoacetyl-CoA synthase and PHA synthase.
• heterologous genes in cyanobacteria and eukaryotic algae is enabled by the introduction of appropriate expression vectors.
• a variety of promoters that function in cyanobacteria can be utilized, including, but not limited to the lac, tac, and trc promoters and derivatives that are inducible by the addition of isopropyl ⁇ -D-1-thiogalactopyranoside (IPTG), promoters that are naturally associated with transposon- or bacterial chromosome-borne antibiotic resistance genes (neomycin phosphotransferase, chloramphenicol acetyltransferase, spectinomycin adenyltransferase, etc.), promoters associated with various heterologous bacterial and native cyanobacterial genes, promoters from viruses and phages, and synthetic promoters.
• IPTG isopropyl ⁇ -D-1-thiogalactopyranoside
• Promoters isolated from cyanobacteria that have been used successfully include the following: secA (secretion; controlled by the redox state of the cell) rbc (Rubisco operon) psaAB (PS I reaction center proteins; light regulated) psbA (Dl protein of PSII; light- inducible)
• transcriptional terminators can be used for expression vector construction.
• examples of possible terminators include, but are not limited to, psbA, psaAB, rbc, secA, and T7 coat protein.
• Expression vectors are introduced into the cyanobacterial strains by standard methods, including, but not limited to, natural DNA uptake, conjugation, electroporation, particle bombardment, and abrasion with glass beads, SiC fibers, or other particles.
• the vectors can be: 1) targeted for integration into the cyanobacterial chromosome by including flanking sequences that enable homologous recombination into the chromosome, 2) targeted for integration into endogenous cyanobacterial plasmids by including flanking sequences that enable homologous recombination into the endogenous plasmids, or 3) designed such that the expression vectors replicate within the chosen host.
• promoters and terminators that function in green algae can be utilized, including, but not limited to promoters and terminators from Chlamydomonas and other algae, promoters and terminators from viruses, and synthetic promoters and terminators.
• Expression vectors are introduced into the green algal strains by standard methods, including, but not limited to, electroporation, particle bombardment, and abrasion with glass beads, SiC fibers, or other particles.
• the vectors can be 1) targeted for site- specific integration into the green algal chloroplast chromosome by including flanking sequences that enable homologous recombination into the chromosome, or 2) targeted for integration into the cellular (nucleus-localized) chromosome.
• promoters from Thalassiosira and other heterokont algae include an alpha- tubulin promoter (SEQ ID NO:1), a beta-tubulin promoter (SEQ ID NO:2), and an actin promoter (SEQ ID NO:3).
• Promoters from Phaeodactylum tricornutum that would be suitable for use in expression vectors include an alpha-tubulin promoter (SEQ ID NO:4), a beta-tubulin promoter (SEQ ID NO:5), and an actin promoter (SEQ ID NO: 6). These sequences are deduced from the genomic sequences of the relevant organisms available in public databases and are merely exemplary of the wide variety of promoters that can be used. The terminators associated with these and other genes, or particular heterologous genes can be used to stop transcription and provide the appropriate signal for polyadenylation and can be derived in a similar manner or are known in the art.
• Expression vectors are introduced into the diatom strains by standard methods, including, but not limited to, electroporation, particle bombardment, and abrasion with glass beads, SiC fibers, or other particles.
• the vectors can be 1) targeted for site-specific integration into the diatom chloroplast chromosome by including flanking sequences that enable homologous recombination into the chromosome, or 2) targeted for integration into the cellular (nucleus-localized) chromosome.
• the host cells used to prepare the cultures of the invention include any photosynthetic organism which is able to convert inorganic carbon into a substrate that is in turn converted to fatty acid derivatives.
• These organisms include prokaryotes as well as eukaryotic organisms such as algae and diatoms.
• Host organisms include eukaryotic algae and cyanobacteria (blue-green algae).
• Representative algae include green algae (chlorophytes), red algae, diatoms, prasinophytes, glaucophytes, chlorarachniophytes, euglenophytes, chromophytes, and dinoflagellates.
• a number of cyanobacterial species are known and have been manipulated using molecular biological techniques, including the unicellular cyanobacteria Synechocystis sp. PCC6803 and Synechococcus elongates PCC7942, whose genomes have been completely sequenced.
• Another group includes
• Still another group includes
• Still another group includes
• various algae including diatoms and green algae can be employed.
• Desirable qualities of the host strain include high potential growth rate and lipid productivity at 25-50 0 C, high light intensity tolerance, growth in brackish or saline water, i.e., in wide range of water types, resistance to growth inhibition by high O 2 concentrations, filamentous morphology to aid harvesting by screens; resistance to predation, ability to be flocculated (by chemicals or 'on-demand autoflocculation'), excellent inorganic carbon uptake characteristics, virus or cyanophage-resistance, tolerance to free fatty acids or other compounds associated with the invention method, and ability to undergo metabolic engineering.
• Metabolic engineering is facilitated by the ability to take up DNA by electroporation or conjugation, lack of a restriction system and efficient homologous recombination in the event gene replacement or gene knockouts are required.
• the fatty acids secreted into the culture medium by the recombinant photosynthetic microorganisms described above can be recovered in a variety of ways.
• a straightforward isolation method by partition using immiscible solvents may be employed.
• particulate adsorbents can be employed. These may be lipophilic particulates or ion exchange resins, depending on the design of the recovery method. They may be circulating in the separated medium and then collected, or the medium may be passed over a fixed bed column, for example, a chromatographic column containing these particulates.
• the fatty acids are then eluted from the particulate adsorbents by the use of an appropriate solvent. Evaporation of the solvent, followed by further processing of the isolated fatty acids and lipids can then be carried out to yield chemicals and fuels that can be used for a variety of commercial purposes.
• the particulate adsorbents may have average diameters ranging from 0.5 mm to 30 mm which can be manufactured from various materials including, but not limited to, polyethylene and derivatives, polystyrene and derivatives, polyamide and derivatives, polyester and derivatives, polyurethane and derivatives, polyacrylates and derivatives, silicone and derivatives, and polysaccharide and derivatives. Certain glass and ceramic materials can also be used as the solid support component of the fat adsorbing objects.
• the surfaces of the particulate adsorbents may be modified so that they are better able to bind fatty acids and lipids. An example of such modification is the introduction of ether- linked alkyl groups having various chain lengths, preferably 8-30 carbons. In another example, acyl chains of various lengths can be attached to the surface of the fat adsorbing objects via ester, thioester, or amide linkages.
• the particulate adsorbents are coated with inorganic compounds known to bind fatty acids and lipids. Examples of such compounds include but are not limited to aluminum hydroxide, graphite, anthracite, and silica.
• the particles used may also be magnetized or otherwise derivatized to facilitate recovery. For instance the particles may be coupled to one member of a binding pair and the adsorbed to a substrate containing the relevant binding partner.
• the fatty acids may be eluted from the particulate adsorbents by the use of an appropriate solvent such as hexane or ethanol.
• the particulate adsorbents may be reused by returning them to the culture medium or used in a regenerated column.
• the solvent containing the dissolved fatty acids is then evaporated, leaving the fatty acids in a purified state for further conversion to chemicals and fuels.
• the particulate adsorbents can be designed to be neutrally buoyant or positively buoyant to enhance circulation in the culture medium.
• a continuous cycle of fatty acid removal and recovery can be implemented by utilizing the steps outlined above.
• the recovered fatty acids may be converted to alternative organic compounds, used directly, or mixed with other components. Chemical methods for such conversions are well understood in the art, and developments of biological methods for such conversions are also contemplated
• the present invention further contemplates a variety of compositions comprising the fatty acids produced by the recombinant photosynthetic microorganisms described herein, and uses thereof.
• the composition may comprise the fatty acids themselves, or further derivatives of the fatty acids, such as alcohols, alkanes, and alkenes which can be generated from the fatty acids produced by the microorganisms by any methods that are known in the art, as well as by development of biological methods of conversion.
• fatty acids may be converted to alkenes by catalytic hydro genation and catalytic dehydration.
• the composition may serve, for example, as a biocrude.
• the biocrude can be processed through refineries that will convert the composition compounds to various petroleum and petrochemical replacements, including alkanes, olefins and aromatics through processes including hydrotreatment, decarboxylation, isomerization and catalytic cracking and reforming.
• the biocrude can be also converted to ester-based fuels, such as fatty acid methyl ester (commercially known as biodiesel), through established chemical processes including transesterification and esterification.
• derivatives of the fatty acids of the present invention include C8 chemicals, such as octanol, used in the manufacture of esters for cosmetics and flavors as well as for various medical applications, and octane, used primarily as a co-monomer in production of polyethylene.
• Derivatives of the fatty acids of the present invention may also include ClO chemicals, such as decanol, used in the manufacture of plasticizers, surfactants and solvents, and decene, used in the manufacture of lubricants.
• Biocrudes are biologically produced compounds or a mix of different biologically produced compounds that are used as a feedstock for refineries in replacement of, or in complement to, crude oil or other forms of petroleum.
• these feedstocks have been pre-processed through biological, chemical, mechanical or thermal processes in order to be in a liquid state that is adequate for introduction in a petroleum refinery.
• the fatty acids of the present invention can be a biocrude, and further processed to a biofuel composition.
• the biofuel can then perform as a finished fuel or a fuel additive.
• Finished fuel is defined as a chemical compound or a mix of chemical compounds (produced through chemical, thermochemical or biological routes) that is in an adequate chemical and physical state to be used directly as a neat fuel or fuel additive in an engine. In many cases, but not always, the suitability of a finished fuel for use in an engine application is determined by a specification which describes the necessary physical and chemical properties that need to be met.
• engines are: internal combustion engine, gas turbine, steam turbine, external combustion engine, and steam boiler.
• finished fuels include: diesel fuel to be used in a compression-ignited (diesel) internal combustion engine, jet fuel to be used in an aviation turbine, fuel oil to be used in a boiler to generate steam or in an external combustion engine, ethanol to be used in a flex- fuel engine.
• diesel fuel to be used in a compression-ignited (diesel) internal combustion engine jet fuel to be used in an aviation turbine
• fuel oil to be used in a boiler to generate steam or in an external combustion engine fuel oil to be used in a boiler to generate steam or in an external combustion engine
• ethanol to be used in a flex- fuel engine.
• ASTM standards mainly used ion the US
• EN standards mainly used in Europe.
• Fuel additive refers to a compound or composition that is used in combination with another fuel for a variety of reasons, which include but are not limited to complying with mandates on the use of biofuels, reducing the consumption of fossil fuel-derived products or enhancing the performance of a fuel or engine.
• fuel additives can be used to alter the freezing/gelling point, cloud point, lubricity, viscosity, oxidative stability, ignition quality, octane level, and flash point.
• Additives can further function as antioxidants, demulsifiers, oxygenates, thermal stability improvers, cetane improvers, stabilizers, cold flow improvers, combustion improvers, anti-foams, anti-haze additives, icing inhibitors, injector cleanliness additives, smoke suppressants, drag reducing additives, metal deactivators, dispersants, detergents, demulsifiers, dyes, markers, static dissipaters, biocides, and/or corrosion inhibitors.
• the Cuphea hookeriana FatB2 gene encoding an acyl-ACP thioesterase (ChFatB2) enzyme was modified for optimized expression in Synechococcus elongatus PCC 7942.
• ChFatB2 acyl-ACP thioesterase
• the nucleotide sequence of this derivative of the ChFatB2 gene (hereafter ChFatB2-7942) is provided as SEQ ID NO:7.
• the protein sequence encoded by this gene is provided in SEQ ID NO: 8.
• trc Two different versions of the trc promoter, trc (Egon, A., et al., Gene (1983) 25:167-178) and "enhanced trc" (hereafter trcE, from pTrcHis A, Invitrogen) were used to drive the expression of ChFatB2-7942 in S. elongatus PCC 7942.
• the trc promoter is repressed by the Lac repressor protein encoded by the laclq gene and can be induced by the addition of isopropyl ⁇ -D-1-thiogalactopyranoside (IPTG).
• IPTG isopropyl ⁇ -D-1-thiogalactopyranoside
• the trcE promoter is a derivative of trc designed to facilitate expression of eukaryotic proteins in E. coli and is also inducible by IPTG.
• SEQ ID NO:9 represents the sequence between and including the NSl recombination sites of pSGI-YCOl.
• the constructed plasmid containing the trc::ChFatB2-7942 expression cassette and laclq gene is designated pSGI-YC09.
• SEQ ID NO: 10 represents the sequence between and including the NSl recombination sites of pSGI-YC09.
• Each of the plasmids pSGI-YCOl and pSGI-YC09, along with the control vector pAM2314, were introduced into wild-type S. elongatus PCC 7942 cells as described by Golden and Sherman (/. Bacterid. (1984) 158:36-42). Both recombinant and control strains were pre-cultivated in 100 mL of BG-Il medium supplied with spectinomycin (5 mg/L) to late-log phase (OD 730nIn 1-0) on a rotary shaker (150 rpm) at 3O 0 C with constant illumination (60 ⁇ E m "2 sec "1 ).
• Free fatty acids were separated from filtered cell cultures using liquid- liquid extraction. Five mL of the filtrate were mixed with 125 ⁇ L of 1 M H 3 PO 3 and 0.25 mL of 5 M NaCl, followed by addition of 2 mL of hexane and thorough mixing.
• a 0.2 ⁇ l sample of the hexane was injected using a 40:1 split ratio onto a DB-FFAP column (J&W Scientific, 15 m x 250 ⁇ m x 0.25 ⁇ m), with a temperature profile starting at 15O 0 C for 0.5 min, then heating at 15°C/min to 23O 0 C and holding for 7.1 min (l.l mL/min He).
• Table 1-1 Medium-chain fatty acid secretion in various strains of S. elongatus
• trcE::ChFatB2-7942 and trc::ChFatB2-7942 fusion fragments, together with the laclq gene, were cloned into the shuttle vector pSGI-YC03 (SEQ ID NO: 11), which enables transformation of Synechocystis sp. PCC 6803 via double homologous recombination-mediated integration into the "RSl" site of the chromosome (Williams, Methods Enzymol. (1988) 167:766-778).
• the constructed plasmid containing the trcE::ChFatB2-7942 expression cassette and laclq gene is designated pSGI-YC08.
• SEQ ID NO: 12 represents the sequence between and including the RSl recombination sites of pSGI- YC08.
• the constructed plasmid containing the trc::ChFatB2-7942 expression cassette and laclq gene is designated pSGI-YC14.
• SEQ ID NO: 13 represents the sequence between and including the RSl recombination sites of pSGI-YC14.
• Cultures were sampled 0, 72, and 144 hours after IPTG induction and then filtered through Whatman ® GF/B filters using a Millipore vacuum filter manifold. Filtrates were collected in screw top culture tubes for gas chromatographic (GC) analysis. Free fatty acids (FFA) were separated from the filtered culture supernatant solutions by liquid-liquid extraction.
• GC gas chromatographic
• ND represents "not detected” ( ⁇ 1 mg/L).
• trc::ChFatB2-7942 and trcE::ChFatB2-7942 fusion fragments were PCR amplified using primers RS3-3F (SEQ ID NO: 14) and 4YC- rrnBter-3 (SEQ ID NO:15) from pSGI-YC14 and pSGI-YC08, respectively, and then cloned into the shuttle vector pEL17, which enables transformation of A. variabilis ATCC 29413 via double homologous recombination-mediated integration into the nifUl locus of the chromosome (Lyons and Thiel, J. Bacterid.
• the constructed plasmids are designated pSGI-YC69 and pSGI-YC70 for trc::ChFatB2-7942 and trcE: :ChFatB2-7942, respectively.
• Each of the plasmids pSGI-YC69, pSGI-YC70, along with the control vector pEL17, are introduced into wild- type A. variabilis ATCC 29413 cells via tri-parental conjugation, as described by Elhai and WoIk ⁇ Methods Enzymol. (1988) 167:747-754).
• Primer pairs 918-15 (SEQ ID NO:16) / 918-13 (SEQ ID NO:17) and 918- 25 (SEQ ID NO:18) / 918-23 (SEQ ID NO:19) were used to amplify two DNA fragments corresponding to a 5' portion (1-480 bp) and a 3' portion (903-1521 bp) of the coding region of synpcc7942_0918, respectively.
• the cat fragment was amplified from plasmid pAM1573 (Mackey et al., Methods MoI. Biol.
• the resulting 2,840-bp blunt-end PCR fragment (SEQ ID NO:22) was then ligated into pUC19 (Yanisch-Perron et al, Gene 33:103-119), which has been digested with both HindlII and EcoRI to remove the multiple cloning sites and subsequently blunted with T4 DNA polymerase, to yield plasmid pSGI-YC04.
• Plasmid pSGI-YC04 was introduced into S. elongatus strain SGC-YCl-2, which harbors a copy of trcE::ChFatB2-7942 integrated into NSl (see Example 1). The resulting strain was designated SGC-YC4-7. Fatty acid production assays and GC analyses were performed as described in Example 1. The results of GC analyses indicating the levels of FFAs in cultures of various S. elongatus strains 168 hours after IPTG induction are shown in Table 4-1. It is possible that inactivation of the acyl-ACP synthetase gene has a larger impact on secretion of long-chain fatty acids than on secretion of medium-chain fatty acids.
• ND represents "not detected” ( ⁇ 1 mg/L).
• PCC 6803 was amplified from genomic DNA using PCR with primers NBOOl (SEQ ID NO:23) and NB002 (SEQ ID NO:24). This fragment was cloned into the pCR2.1 vector (Invitrogen) to yield plasmid pSGI-NB3 and subsequently cut with the restriction enzyme Mfel.
• a chloramphenicol resistance marker cassette containing the cat gene and associated regulatory control sequences was amplified from plasmid pAM1573 (Andersson, et al., Methods Enzymol. (2000) 305:527-542) to contain flanking Mfel restriction sites using PCR with primers NBOlO (SEQ ID NO:25) and NBOIl (SEQ ID NO:26).
• the cat gene expression cassette was then inserted into the Mfel site of pSGI-NB3 to yield pSGI-NB5 (SEQ ID NO:27).
• the pSGI-NB5 vector was transformed into trcE::ChFatB2-7942-containing Synechocystis strain SGC-YClO-5 (see Example 1) according to Zang et al., J Microbiology (2007) 45:241-245. Insertion of the chloramphenicol resistance marker into the Slrl609 gene through homologous recombination was verified by PCR screening of insert and insertion site. The resulting strain was designated SGC-NB 10-4, which was tested in liquid BG-11 medium for fatty acid secretion. All liquid medium growth conditions used a rotary shaker (150 rpm) at 3O 0 C with constant illumination (60 ⁇ E-m ⁇ -sec "1 ).
• Free fatty acids were separated from the filtered culture supernatant solutions by liquid-liquid extraction for GC/FID (flame ionization detector) analysis. For each sample, 2 mL filtered culture was extracted with a mixture of 50 ⁇ l phosphoric acid (1 M), 100 ⁇ l NaCl (5 M) and 2 mL hexane.
• a 0.2 ⁇ l sample was injected using a 40:1 split ratio on to a DB-FFAP column (J&W Scientific, 15 m x 250 ⁇ m x 0.25 ⁇ m), with a temperature profile starting at 15O 0 C for 0.5 min, then heating at 15°C/min to 23O 0 C and holding for 7.1 min (1.1 mL/min He).
• ND represents "not detected” ( ⁇ 1 mg/L).
• a DNA fragment comprising a functional operon was synthesized such that it contained the following elements in the given order: the trc promoter, the Cuphea lanceolata 3-ketoacyl-acyl carrier protein synthase IV gene (ClKas-IV, GenBank Accession No. CAC59946) codon-optimized for expression in Synechococcus elongatus PCC 7942, and the rpsl4 terminator (SEQ ID NO:28) from Synechococcus sp. WH8102.
• the nucleotide sequence of this entire functional operon, along with various flanking restriction enzyme recognition sites, is provided in SEQ ID NO:29.
• Another DNA fragment comprising a functional operon was synthesized such that it contained the following elements in the given order: the trc promoter, the Helianthus annuus 3-ketoacyl-acyl carrier protein synthase III gene (HaKas-III, GenBank Accession No. ABP93352) codon-optimized for expression in both Synechococcus elongatus PCC 7942 and Synechocystis sp. PCC 6803, and rpsl4 terminator from Synechococcus sp. WH8102.
• the nucleotide sequence of this functional operon, along with various flanking restriction enzyme recognition sites, is provided in SEQ ID NO:30.
• Codon optimization was performed by the use of the "Gene Designer” (version 1.1.4.1) software program provided by DNA2.0, Inc.
• the functional operon (expression cassette) containing the codon-modified ClKas-IV gene as represented in SEQ ID NO:29 was digested by the restriction enzymes Spel and Xbal and inserted into plasmid pSGI-YC39 between the restriction sites Spel and Xbal to form plasmid pSGI-BL26, which enables integration of the functional operon into the Synechocystis sp.
• PCC 6803 chromosome at the "RS2" recombination site (Aoki, et al, J. Bacteriol (1995) 177:5606- 5611).
• the plasmid pSGI-BL27 containing the DNA fragment represented in SEQ ID NO: 30 was constructed in the same way.
• Plasmid pSGI-BL43 contains the trcE promoter, the codon-optimized ClKas-IV gene, and the rpsl4 terminator as represented in SEQ ID NO:31 and was made by inserting a Spel/Ncol trcE fragment from pTrcHis A (Invitrogen) into Spel/NcoI-digested pSGI- BL26.
• An additional plasmid, pSGI-BL44 contains the trcE promoter, the optimized ClKas-IV gene, the S.
• elongatus PCC 7942 kaiBC intergenic region, the optimized HaKas- III gene, and the rpsl4 terminator as represented in SEQ ID NO:32 and was made by inserting a BamHI/SacI fragment (containing the S. elongatus kaiBC intergenic region, the HaKas-III gene, and the rpsl4 terminator) generated via PCR amplification into Bglll/Sacl- digested pSGI-BL43.
• the PCR primers used to generate the DNA fragment containing the kaiBC region, HaKas-III, and rpsl4 terminator are provided as SEQ ID NO:33 and SEQ ID NO:34.
• Results indicating the levels of secreted octanoic acid and decanoic acid in culture supernatants 144 hours after culture inoculation are shown in Table 6-1.
• the ClKas- IV and HaKas-III genes present in the indicated strains were under the control of the trc promoter.
• ND represents "not detected” ( ⁇ 1 mg/L).
• ND represents "not detected” ( ⁇ 1 mg/L).
• ND represents "not detected” ( ⁇ 1 mg/L).
• a synthetic gene that encodes a derivative of the ChFatB2 enzyme with specificity for medium-chain (8:0-10:0) acyl-ACPs is expressed in various diatoms (Bacillariophyceae) by constructing and utilizing expression vectors comprising the ChFatB2 gene operably linked to gene regulatory regions (promoters and terminators) that function in diatoms.
• the gene is optimized for expression in specific diatom species and the portion of the gene that encodes the plastid transit peptide region of the native ChFatB2 protein is replaced with a plastid transit peptide that functions optimally in diatoms.
• the protein encoded by this gene referred to hereafter as ChFatB2-Thal, is provided in SEQ ID NO:36.
• the ChFatB2-Thal gene was placed between the T. pseudonana alpha-tubulin promoter and terminator regulatory sequences.
• the alpha-tubulin promoter was amplified from genomic DNA isolated from T. pseudonana CCMP 1335 by use of primers PRl (SEQ ID NO:37) and PR3 (SEQ ID NO:38), whereas the alpha-tubulin terminator was amplified by use of primers PR4 (SEQ ID NO:39) and PR8 (SEQ ID NO:40).
• the Kpnl/BamHI fragment from the alpha-tubulin promoter amplicon, the BamHI/Xbal fragment from the alpha-tubulin terminator and the large fragment from Kpnl/Xbal- cut pUC118 were then combined to form pSGI-PR5.
• the NcoI/BamHI fragment from ChFatB2-Thal gene was then inserted into NcoI/BamHI-digested pSGI-PR5 to form pSGI- PR16.
• NAT nourseothricin acetyltransferase
• pSGI-PR16 and pSGI-PR7 were co-transformed into T. pseudonana CCMP 1335 by means of particle bombardment essentially as described by Poulsen, et al., (J. Phycol. (2006) 42:1059-1065). Transformed cells were selected on agar plates in the presence of 100 mg/L nourseothricin (ClonNAT, obtained from Werner BioAgents, Germany). The presence of the ChFatB2-Thal gene in cells was confirmed by the use of PCR. Transformants were grown in ASW liquid medium (Darley and Volcani, Exp. Cell Res.
• a synthetic gene that encodes a derivative of the ChFatB2 enzyme with specificity for medium-chain (8:0-10:0) acyl-ACPs is expressed in green algae (Chlorophyceae) by constructing and utilizing expression vectors comprising the ChFatB2 gene operably linked to gene regulatory regions (promoters and terminators) that function in green algae.
• the gene is optimized for expression in specific green algal species and the portion of the gene that encodes the plastid transit peptide region of the native ChFatB2 protein is replaced with a plastid transit peptide that functions optimally in green algae.
• the nucleotide sequence provided as SEQ ID NO:42 represents a derivative of the ChFatB2 gene optimized for expression in Chlamydomonas reinhardtii and in which the native plastid transit peptide-encoding region of the gene has been replaced with the plastid transit peptide associated with the gamma subunit of the coupling factor portion (CFl) of the chloroplast ATP synthase from C. reinhardtii (GenPept Accession No. XP 001696335).
• the protein encoded by this gene is provided in SEQ ID NO:43.
• a 1.4-kbp DNA fragment spanning an area upstream and into the coding region of the 1,4-alpha-glucan branching enzyme gene (glgB, Cyanobase gene designation sll0158) from Synechocystis sp.
• PCC6803 was amplified from genomic DNA using PCR with primers glgB-5 (SEQ ID NO:44) and glgB-3 (SEQ ID NO:45). This fragment was cloned into the pCR4-Topo vector (Invitrogen) to yield plasmid pSGI-BL32 and subsequently cut with the restriction enzyme Aval.
• a spectinomycin resistance marker cassette containing the aadA gene and associated regulatory control sequences was digested by HindIII from plasmid pSGI-BL27. Both of the linear fragments were treated with the Quick BluntingTM Kit (New England Biolabs). The aadA gene expression cassette was then inserted into the Aval site of pSGI-BL32 to yield pSGI-BL33. The portion of pSGI-BL33 that inserts into and inactivates the glgB gene is provided as SEQ ID NO:46).
• the pSGI-BL33 vector was transformed into wild-type Synechocystis PCC 6803 and into trcE::ChFatB2-7942-containing Synechocystis strain SGC-YClO-5 (see Example 1) according to Zang, et al, J. Microbiology (2007) 45:241-245. Insertion of the spectinomycin resistance marker into the SIlOl 58 (glgB) gene via homologous recombination was verified by PCR screening of insert and insertion site. Verified knockout strains were tested in liquid BG-11 medium for secretion of fatty acids.
• Free fatty acids were separated from the filtered culture supernatant solutions by liquid-liquid extraction for GC/FID analysis.
• 2 mL of filtered culture were extracted with a mixture of 50 ⁇ L phosphoric acid (1 M), 100 ⁇ L NaCl (5 M) and 2 mL hexane.
• a 0.2 ⁇ l sample was injected using a 40:1 split ratio on to a DB-FFAP column (J&W Scientific, 15 m x 250 ⁇ m x 0.25 ⁇ m), with a temperature profile starting at 15O 0 C for 0.5 min, then heating at 15°C/min to 23O 0 C and holding for 7.1 min (1.1 niL/min He).
• ND represents "not detected” ( ⁇ 1 mg/L).
• ND represents "not detected” ( ⁇ 1 mg/L).
• a spike solution was formulated by dissolving 75 mg/L octanoic acid and 75 mg/L decanoic acid in BG-Il medium supplemented with 300 mM NaCl and adjusting the pH to 5.8. 50 mg of each of the resins listed in Table 1 were weighed into a 50 mL centrifuge tube and combined with 1.0 mL of methanol and shaken gently. The excess methanol was decanted and the resins were dried under a 25 in Hg vacuum, room temperature, overnight. 50 mL of the spike solution was then added to each of the resins and incubated with gentle shaking at 31°C for 24 hours.
• Synechocystis sp. strain SGC-YC10-5 which contains the ChFatB2-7942 gene as described in Example 1, was cultured in BG-Il with and without Dowex ® Optipore ® V503 resin. 400 mL of fresh culture was induced with 5 mM IPTG and incubated at room temperature for 1 hour to allow for uptake of the inducer. The culture was then divided into four 1,000 mL baffled Erlenmeyer flasks with PTFE vent caps. To two of the flasks, approximately 400 mg of Dowex ® Optipore ® V503 were added. The adsorbent resin in the test flasks was recovered and exchanged for fresh resin daily for 10 days.
• Table 10-3 above reveals a clear relationship between free fatty acid adsorption capacity and pH. This relationship results from the inefficiency of extraction of the ionized form of the free fatty acids. Many potential production hosts require a pH significantly higher than the pKa of free fatty acids in order to survive and reproduce. An extreme example of this would be the alkalophilic cyanobacteria such as those belonging to the genera Synechococcus, Synechocystis, Spirulina, and many others, which prefer a pH between 9 and 11 for optimum growth.
• Figure 5 outlines an embodiment of the invention wherein this problem is solved by recycling a portion of the culture first through a vessel where it is contacted with concentrated CO 2 gas to lower the pH, then through a stationary adsorbent column wherein the protonated free fatty acids are captured.
• the C ⁇ 2 -enriched, free fatty acid-depleted suspension is then returned to the bulk culture.
• the pressure inside the gas-liquid contactor can be controlled independently to provide a constant pH in the stream exiting the adsorption column. Further, the pressure of the post-column flash vessel can be controlled so as to provide a supply of CO 2 which is titrated to the CO 2 consumption rate of the bulk culture through PID control of pH, dissolved CO 2 , off-gas CO 2 , or any combination of the three. The excess CO 2 can then be recycled.
• Vessel E-I was filled with 4L of a spike solution containing 700 mg/L octanoic acid dissolved in 100 mM NaCl, pH 11.1.
• Column Cl was filled with 45.2 g of Dowex ® Optipore ® V503 polymeric resin. The resin was activated with two column volumes of methanol, followed by a wash of three column volumes of 100 mM NaCl, pH 11.1.
• Liquid- gas contact vessel E2 was then filled with 200 mL of spike solution and 34.7 psia of CO 2 .
• a synthetic gene that encodes a derivative of a FatA-type plant acyl-ACP TE enzyme with specificity for oleoyl-ACP is expressed in various photosynthetic microorganisms by constructing and utilizing expression vectors comprising a FatA gene operably linked to gene regulatory regions (promoters and terminators) that function in the host photosynthetic microorganism.
• the gene is optimized for expression in the host photosynthetic microorganism and the portion of the gene that encodes the plastid transit peptide region of the native FatA protein is removed for expression in cyanobacteria or replaced with a plastid transit peptide that functions effectively in the host eukaryotic photosynthetic microorganisms.
• Genes that could be used for this purpose include, but are not limited to, those that encode the following acyl-ACP TEs (referred to by GenPept Accession Numbers): NP_189147.1, AAC49002, CAA52070.1, CAA52069.1, 193041.1, CAC39106, CAO17726, AAC72883, AAA33020, AAL79361, AAQ08223.1, AAB51523, AAL77443, AAA33019, AAG35064, and AAL77445.
• GenPept Accession Numbers referred to by GenPept Accession Numbers: NP_189147.1, AAC49002, CAA52070.1, CAA52069.1, 193041.1, CAC39106, CAO17726, AAC72883, AAA33020, AAL79361, AAQ08223.1, AAB51523, AAL77443, AAA33019, AAG35064, and AAL77445.

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