JP2007089580A - Method and apparatus for culturing photosynthetic microorganism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To expand a culturing technology to effectively utilize energy of light. <P>SOLUTION: Proliferation of the photosynthetic microorganisms is promoted by comprising a sample containing one or more kinds of the photosynthetic microorganisms using Fe(II) or Fe(III) for the photosynthesizing reaction in a culture medium and then electrochemically regulating the ratio Fe(II)/Fe(III) of the Fe(II) to Fe(III) contained in the medium while irradiating the medium with light. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method and apparatus for culturing photosynthetic microorganisms. More specifically, the present invention relates to an improvement of a culture method for improving energy efficiency.

The amount of light energy that falls from the sun onto the surface of the earth is very large at 1.5 × 10 ¹⁸ kW per year (see Figure 4). In order to efficiently convert this energy into useful substances or chemical energy to save energy and preserve the environment, various studies on the photosynthetic functions of living organisms have been conducted. For example, a technique relating to a microalga such as chlorella and a culture method thereof has been proposed (see, for example, Patent Document 1).

JP 2001-161347 A

  However, while the culture techniques as described above are proposed, there is always a need for a technique that can use light energy more efficiently than the current situation in order to further save energy and protect the environment. For example, it may be possible to sufficiently meet such needs if the conventional culture technique can be further expanded.

  Accordingly, an object of the present invention is to provide a culture method and a culture apparatus for photosynthetic microorganisms that can utilize light energy more efficiently by extending culture techniques.

  In order to achieve this object, the present inventor conducted various studies and experiments. Currently, microorganisms used in the food and pharmaceutical industries are considered to be 1% or less of all microorganisms existing in nature. For this reason, in order to effectively utilize the enormous amount of microbial resources remaining in the environment, development of a new microbial isolation technique is required. Under such circumstances, the inventor has focused on growing unknown microorganisms in the environment using iron respiration (a respiration form using Fe (III) as a final electron acceptor as an alternative to oxygen). When an environmental sample containing various photosynthetic microorganisms was placed in an electrocultivation apparatus that enabled continuous electrochemical supply of Fe (III) and irradiated with light, certain photosynthetic microorganisms were selectively It came to the knowledge that it proliferated.

  The present invention is based on such knowledge, and the method for culturing photosynthetic microorganisms according to claim 1 is a sample containing one or more photosynthetic microorganisms using Fe (II) or Fe (III) in the photosynthetic reaction. The ratio of Fe (II) and Fe (III) contained in the medium is controlled electrochemically while irradiating light, and the growth of photosynthetic microorganisms is controlled. It is to promote.

  A photosynthetic microorganism that uses Fe (II) in its photosynthetic reaction, that is, a photosynthetic microorganism that uses Fe (II) as an electron donor in the photosynthetic reaction oxidizes Fe (II) to Fe (III) during its growth. Therefore, the ratio Fe (II) / Fe (III) of Fe (II) and Fe (III) contained in the medium is controlled electrochemically, that is, Fe (III) is electrochemically converted to Fe (II) By regenerating (reducing), it is possible to continuously supply Fe (II) to the photosynthetic microorganism, to activate the photosynthesis, and to promote the growth of the photosynthetic microorganism.

  In addition, photosynthetic microorganisms that use Fe (III) in their photosynthetic reactions, that is, photosynthetic microorganisms that use Fe (III) as an electron acceptor in the photosynthetic reaction, reduce Fe (III) to Fe (II) during their growth. To do. Therefore, the ratio Fe (II) / Fe (III) of Fe (II) and Fe (III) contained in the medium is controlled electrochemically, that is, Fe (II) is converted to Fe (III) electrochemically. By regenerating (oxidizing), it is possible to continuously supply Fe (III) to the photosynthetic microorganism, to activate the photosynthesis, and to promote the growth of the photosynthetic microorganism.

  Here, the sample containing one or more kinds of photosynthetic microorganisms using Fe (II) or Fe (III) in the photosynthetic reaction means an environmental sample, a sample containing a plurality of kinds of photosynthetic microorganisms, and Fe (II). Samples containing one or more photosynthetic microorganisms used for the photosynthetic reaction, samples containing one or more photosynthetic microorganisms using Fe (III) for the photosynthetic reaction, Fe (II) used for the photosynthetic reaction It means a sample in which one or more photosynthetic microorganisms and one or more photosynthetic microorganisms using Fe (III) in their photosynthetic reaction are mixed.

  In the said invention, it is preferable to culture | cultivate a photosynthetic microorganism under anaerobic conditions as described in Claim 2. In this case, the photosynthesis of a photosynthetic microorganism using Fe (II) as an electron donor or a photosynthetic microorganism using Fe (III) as an electron acceptor in the photosynthesis reaction can be further activated. Therefore, it is possible to further promote the growth of photosynthetic microorganisms.

  In addition, as described in claim 3, chlorella as a photosynthetic microorganism is cultivated as a photosynthetic microorganism at the National Institute of Advanced Industrial Science and Technology, Patent Biological Deposit Center on August 8, 2006, under the accession number FERM P-20984. be able to. This chlorella is a photosynthetic microorganism that uses Fe (III) for its photosynthetic reaction, and it can further activate photosynthesis by electrochemically supplying Fe (III) that functions as the final electron acceptor. it can. Hereinafter, in the present specification, this chlorella will be referred to as “chlorella H-1 strain”.

  Further, as described in claim 4, Rhodovulum iodosum, Rhodovulum robiginosum (Int J Syst Bacteriol. 1999 Apr; 49 Pt 2: 729-35.), Rhodopseudomonas palustris strain TIE-1 (Appl Environ Microbiol. 2005 Aug; 71 (8): 4487-96) can be cultured. Rhodovulum iodosum, Rhodovulum robiginosum, Rhodopseudomonas palustris strain TIE-1 is a photosynthetic microorganism that uses Fe (II) for its photosynthetic reaction, and by continuously supplying Fe (II) that functions as an electron donor electrochemically , Photosynthesis can be further activated.

  Next, an apparatus for culturing photosynthetic microorganisms according to claim 5 comprises: an electroculture tank formed of a light transmissive material; an ion exchange membrane that divides the electroculture tank into two layers of a culture tank and a counter electrode tank; An anode provided in the tank, a cathode provided in the counter electrode tank, a potential control device for controlling the potential of the medium in the electric culture tank via the anode and the cathode, and the electric culture tank while transmitting light It consists of an anaerobic box that keeps the surroundings in an anaerobic state, and in a medium containing Fe (II) and / or Fe (III) A sample containing a photosynthetic microorganism is contained, and the ratio of Fe (II) and Fe (III) in the medium is electrochemically determined while irradiating the medium with light under anaerobic conditions. It is characterized by controlling the growth of photosynthetic microorganisms.

  With this configuration, the ratio of Fe (II) and Fe (III) in the medium, Fe (II) / Fe (III), is controlled electrochemically while irradiating the medium with light under anaerobic conditions. Thus, the growth of photosynthetic microorganisms can be promoted.

  According to the first aspect of the present invention, it is possible to propose a new photosynthesis system culture technique that activates photosynthesis by compositing culture systems. In other words, the conventional electroculture technology that controls the photosynthesis by electrochemically controlling the Fe (II) / Fe (III) ratio Fe (II) / Fe (III) contained in the medium is further expanded. Therefore, it is possible to provide a culture technique for photosynthetic microorganisms that can use light energy more efficiently and effectively.

  Furthermore, it is possible to selectively propagate photosynthetic microorganisms that use Fe (II) or Fe (III) in the photosynthetic reaction from environmental samples and samples in which a plurality of types of photosynthetic microorganisms coexist. Also, not only one type of photosynthetic microorganism that uses Fe (II) for its photosynthetic reaction, but also multiple types of organisms that proliferate simultaneously. It is also possible to make it. Furthermore, it is also possible to selectively propagate only one photosynthetic microorganism from a sample containing photosynthetic microorganisms that use Fe (II) in their photosynthetic reaction and photosynthetic microorganisms that use Fe (III) in their photosynthetic reaction. Is possible.

  Next, according to the invention described in claim 2, since the culture is performed in an anaerobic state, a photosynthetic microorganism using Fe (II) as an electron donor in a photosynthesis reaction, or Fe (III) as an electron acceptor. It is possible to further activate the photosynthesis of the photosynthetic microorganism, and to further promote the growth of the photosynthetic microorganism.

  In addition, according to the invention described in claim 3, the growth of the chlorella H-1 strain can be promoted.

  According to the invention described in claim 4, it is possible to promote the growth of Rhodovulum iodosum, Rhodovulum robiginosum, Rhodopseudomonas palustris strain TIE-1.

  Next, according to the culture apparatus of claim 5, the ratio Fe (II) / Fe (III) of Fe (II) and Fe (III) in the medium is changed while irradiating the medium with light under anaerobic conditions. It can be controlled electrochemically to promote the growth of photosynthetic microorganisms. Therefore, the conventional electroculture technology that controls the photosynthesis by electrochemically controlling the Fe (II) / Fe (III) ratio Fe (II) / Fe (III) contained in the medium is further expanded. Thus, it is possible to provide a culture apparatus for photosynthetic microorganisms that can establish the established culture technique and can use light energy more efficiently and effectively.

  Hereinafter, the configuration of the present invention will be described in detail based on embodiments shown in the drawings.

  FIG. 1 shows an apparatus for culturing photosynthetic microorganisms according to the present invention. The culture apparatus 1 is provided in an electric culture tank 2, an electric culture tank 2 formed of a light-transmitting material, an ion exchange membrane 3 that partitions the electric culture tank 2 into two layers, a culture tank 2a and a counter electrode tank 2b. The anode 4, the cathode 5 provided in the counter electrode tank, the potential control device 6 for controlling the potential of the medium (culture medium) 8 in the electric culture tank 2 through the anode 4 and the cathode 5, and transmitting light. The anaerobic box 7 keeps the periphery of the electric culture tank 2 in an anaerobic state.

  The electric culture tank 2 is a tank formed of a light transmissive material such as an acrylic plate or a glass plate. For example, in this embodiment, a tank having a round bottom as shown in FIG. 1 is used as an example. However, this is merely an example, and the material and shape are not particularly limited as long as the amount of light is sufficient to transmit light. . A medium (culture medium) 8 used for culture is poured into the electric culture tank 2.

  The medium 8 contains at least one of Fe (II) serving as an electron donor and Fe (III) serving as an electron acceptor in the photosynthetic reaction of the photosynthetic microorganism. Further, any component that does not adversely affect the regeneration (oxidation / reduction) of Fe (II) or Fe (III) may be contained. In addition, the form of the medium may be in a solid state or a liquid-solid coexisting state other than liquid, as long as free movement of Fe (II) or Fe (III) is not hindered. From this point of view, it is preferably used in a liquid state. In the following examples, Fe (III) is included in the medium as a complex such as Fe (III) -EDTA, but Fe (II) or Fe (III) is stably present in the medium. If it is possible, it is not limited to this.

  The ion exchange membrane 3 is provided to divide the electric culture tank 2 into two layers of a culture tank 2a and a counter electrode tank 2b, and the culture target is placed in the culture tank 2a and cultured. Furthermore, the ion exchange membrane 3 is a filter that allows the ions in the medium 8 to pass but does not allow the photosynthetic microorganisms to be cultured to pass to the counter electrode 2b side, that is, to the counter electrode 2b of the photosynthetic microorganisms to be cultured included in the culture vessel 2a. It functions as a filter that prevents the movement of.

  The anode 4 and the cathode 5 are a pair of plate-like plates provided in the electric culture tank 2 for applying a voltage to the electric culture tank 2 to regenerate (oxidize and reduce) Fe (II) and Fe (III). For example, a carbon plate can be used as the material of the electrode, but the material is not limited to this. Both the anode 4 and the cathode 5 are connected to a potential control device 6. The potential control device 6 adjusts the potential by applying a voltage between the anode 4 and the cathode 5. In addition, a reference electrode 9 for referring to a potential in the electric culture tank 2 is also connected to the potential control device 6. This reference electrode 9 is installed in the culture tank 2a where the photosynthetic microorganisms to be cultured are present.

  When the subject of culture is a photosynthetic microorganism that uses Fe (II) as an electron donor in a photosynthetic reaction, Fe (II) is oxidized to Fe (III) when the photosynthetic microorganism grows. Therefore, Fe (III) is regenerated (reduced) to Fe (II), and Fe (II) is continuously supplied to the photosynthetic microorganism. Specifically, the potential in the culture tank 2a, that is, the potential detected by the reference electrode 9 is about −0.4V to −0.8V, which is a potential for reducing Fe (III) to Fe (II). In this manner, a voltage is applied to the anode 4 and the cathode 5. As a result, Fe (III) can be regenerated (reduced) to Fe (II), and Fe (II) can be continuously supplied to the photosynthetic microorganism.

  In addition, when the subject of culture is a photosynthetic microorganism that uses Fe (III) as an electron acceptor in a photosynthetic reaction, Fe (III) is reduced to Fe (II) when the photosynthetic microorganism grows. Therefore, Fe (II) is regenerated (oxidized) to Fe (III), and Fe (III) is continuously supplied to photosynthetic microorganisms. Specifically, the potential in the culture tank 2a, that is, the potential detected by the reference electrode 9 is about 0.1V to 1.0V, which is a potential for oxidizing Fe (II) to Fe (III). A voltage is applied to the anode 4 and the cathode 5. This makes it possible to regenerate (oxidize) Fe (II) to Fe (III) and continuously supply Fe (III) to the photosynthetic microorganism.

Here, the relationship between the iron shown in FIG. 2 and the photosynthetic system will be described. When the culture target is a photosynthetic microorganism using Fe (III) as an electron acceptor, water molecules (H ₂ O) in the medium 8 will provide electrons as shown in the lower left of the figure, After passing through the flow in the figure, it is supplied to Fe (III) and reduced to Fe (II). On the other hand, if the subject of culture is a photosynthetic microorganism that uses Fe (II) as an electron donor, conversely, Fe (II) is used as an oxidizing agent, and electrons are emitted at the initial stage of photosynthesis reaction (lower left in the figure). Will continue to supply.

The anaerobic box 7 is for keeping the periphery of the electric culture tank 2 in an anaerobic state, and is formed of, for example, an acrylic plate that can transmit light. The anaerobic box 7 includes a gas inlet 10 and an outlet 11 that form an anaerobic state. For example, in the case of this embodiment, the gas inflow port 10 is provided on one side surface of the anaerobic box formed in a rectangular parallelepiped shape, and the gas outflow port 11 is provided on the side surface facing this. Further, an inert gas such as nitrogen (N ₂ ) gas or a rare gas is used as a gas for making the periphery of the electric culture tank 2 anaerobic, and this gas is continuously supplied from the inlet 10.

  In this embodiment, both the electric culture tank 2 and the anaerobic box 7 are made light transmissive by an acrylic material or the like, but the light irradiated in this case includes both natural light and artificial light. That is, the term “light irradiation” as used in this specification includes not only active irradiation of light using an illuminating device or the like, but also includes the case where irradiation is performed in an environment where natural light is inserted.

  The culture apparatus 1 as described above creates an anaerobic state in the anaerobic box 7, and electrochemically calculates the ratio Fe (II) / Fe (III) of Fe (II) and Fe (III) contained in the medium. It is possible to control and to irradiate light to a photosynthetic microorganism that uses Fe (II) or Fe (III) for its photosynthetic reaction. Therefore, according to this culturing apparatus 1, under anaerobic conditions, the ratio Fe (II) / Fe (III) of Fe (II) and Fe (III) contained in the medium is controlled electrochemically to the photosynthetic microorganism. It is possible to perform culture in which each method of irradiating light is combined. In such a case, the efficiency of photosynthesis of the photosynthetic microorganism can be improved and the growth thereof can be promoted.

  Therefore, when the culture object (sample) is cultured as an environmental sample or a sample in which a plurality of types of photosynthetic microorganisms are mixed by the culture apparatus 1, photosynthetic microorganisms using Fe (II) or Fe (III) for the photosynthetic reaction. Can be selectively propagated. Also, not only one kind of photosynthetic microorganism that uses Fe (II) for the photosynthetic reaction, but also a plurality of kinds can be propagated simultaneously. Is also possible. Furthermore, it is also possible to selectively propagate only one photosynthetic microorganism from a sample containing photosynthetic microorganisms that use Fe (II) in their photosynthetic reaction and photosynthetic microorganisms that use Fe (III) in their photosynthetic reaction. Is possible.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention. For example, in this embodiment, the culture target is a photosynthetic microorganism, but the present invention is not limited to this, and a photosynthetic bacterium that uses Fe (II) or Fe (III) for the photosynthesis reaction may be the culture target.

  It is also possible to use solar power generation to generate energy for applying a voltage in the culture tank 2a, and to save energy by using light energy more efficiently and effectively. .

  Furthermore, the culture apparatus 1 of the present invention can be used not only as an apparatus for culturing and growing photosynthetic microorganisms, but also as an apparatus for supplying energy generated as a result of the photosynthetic reaction of the photosynthetic microorganisms.

In addition, by optimizing the light irradiation intensity and electrochemically controlling the ratio of Fe (II) and Fe (III) Fe (II) / Fe (III), an optimal environment for the photosynthetic microorganisms to perform the photosynthetic reaction is created. It is possible to increase the proportion of photosynthetic microorganisms in which the photosynthetic reaction is activated. Furthermore, in facilities such as CO ₂ fixation, H ₂ production, useful substance production, wastewater treatment, exhaust gas treatment, etc., photosynthetic microorganisms that use Fe (II) or Fe (III) for their photosynthetic reaction are directly put into the reaction tank. Or by immobilizing this microorganism on a carrier or the like, and irradiating light while controlling the ratio Fe (II) / Fe (III) of Fe (II) and Fe (III) electrochemically, It is possible to efficiently control CO ₂ fixation, H ₂ production, useful substance production, wastewater treatment, exhaust gas treatment, etc. by controlling the photosynthesis reaction with high efficiency using the irradiated light energy. In other words, according to the present invention, it is possible to perform energy production or treatment of harmful substances by a photosynthesis reaction using light energy such as sunlight more efficiently than when only light energy such as sunlight is used. Is possible.

  Although the result of experiment and examination is demonstrated as an Example below, this invention is not limited to a following example.

[Example 1]
[1. Medium adjustment]
First, the medium (culture medium) 8 was prepared as follows. That is, in 1 L of distilled water, (NH ₄ ) ₂ SO ₄ ; 1.0 g, KNO ₃ ; 0.5 g, K ₂ HPO ₄ ; 0.5 g, KH ₂ PO ₄ ; 0.6 g, MgSO ₄ · 7H ₂ O; 0.2 g, CaCl ₂ · 2H ₂ O: 0.01 g, FeSO ₄ · 7H ₂ O; 0.01 ml of inorganic basic medium 8 dissolved in 2 ml of trace metal solution (CuSO ₄ · 5H ₂ O in 1 L of distilled water; 5 mg, CoCl ₂ · 6H ₂ O; 5 mg, NiCl ₂ · 6H ₂ O; 5 mg, NaMoO ₄ · 2H ₂ O; 5 mg, ZnSO ₄ ; 30 mg, MnCl ₂ · 6H ₂ O; Further, Fe (III) -EDTA (iron in a complex state in which Fe (III) was chelated with ethylenediaminetetraacetic acid) was further added to the iron-added medium 8 at 0.84 g / L. In either case, the pH of the medium 8 was adjusted to 7.0 using a dilute hydrochloric acid aqueous solution.

[2. Culture method]
Cultivation was carried out using the culture apparatus 1 shown in FIG. The culture tank 2 is a two-layer system in which the inside of a glass petri dish with an outer diameter of 75 mm and a height of 90 mm is partitioned by a monovalent cation-permeable ion exchange membrane (Asahi Kasei, K-192) 3. The culture tank 2a was used as the counter electrode tank 2b (see FIG. 1). A carbon plate (40 mm x 40 mm, 4 mm thickness) is installed as an anode 4 and a cathode 5 in the culture tank 2a and the counter electrode tank 2b, respectively, and a silver / silver chloride reference electrode (HS-205C, Toa DKK) is installed in the culture tank 2a. ) 9 was installed. By connecting these three electrodes (anode 4, cathode 5 and reference electrode 9) to a potential control device (POTENTIO / GALVANOSTAT model 110, Fuso Seisakusho) 6, the potential of the anode 4 in the electric culture tank 2 is set strictly. It was possible. Regarding the culture, the culture tank 2 was enclosed in an acrylic anaerobic box 7, and the entire anaerobic box 7 was installed inside a positive sunlight incubator (Meibakukan Kikai Kogyo Co., Ltd.) set at 30 ° C. Nitrogen gas was always injected into the anaerobic box 7 (0.2 L / min), and 60-70 μmol / m ² · s of light was constantly radiated to set anaerobic conditions.

[3. Culture using environmental samples]
The culture apparatus 1 was irradiated with light to an environmental sample, and Fe (III) was continuously supplied in a nitrogen gas atmosphere to culture and selectively propagated photosynthetic microorganisms were isolated. From the sequence homology of gene, it was confirmed that it was a new chlorella presumed to be closely related to Chlorella sorkiniana C212 strain, and this was designated as Chlorella sp. H-1 strain (Chlorella H-1 strain). The chlorella H-1 strain was different from normal chlorella in heterotrophic growth and could not grow under dark conditions regardless of aerobic or anaerobic, and was completely light-dependent.

[4. Relationship between Fe and the growth of Chlorella H-1 strain]
Next, in order to analyze the relationship between Fe and the growth of Chlorella H-1 strain, an attempt was made to culture while controlling the amount of Fe (II) / Fe (III) by electroculture. Chlorella sorkiniana C212 strain was used as a reference sample. In Chlorella sorkiniana C212 strain, growth by controlling the amount of Fe was not observed, but in Chlorella H-1 strain, it was produced from Fe (III) by continuously supplying Fe (III), that is, by electrochemical reduction reaction. Regeneration (oxidation) of Fe (II) promoted proliferation.

  From the above, it was confirmed that by using the culture method of the present invention, it is possible to selectively grow photosynthetic microorganisms whose photosynthesis is activated by Fe (III) from environmental samples.

[Example 2]
The ratio Fe (II) / Fe (III) ratio of Fe (II) and Fe (III) contained in the medium 8 is controlled electrochemically, and the influence on the growth of Chlorella H-1 strain is analyzed. Tried. In the culture tank 2a that regenerates (oxidizes) Fe (II) to Fe (III) based on the potential region where iron oxidation occurs, Fe (III) is based on the potential region where iron reduction occurs. In the culture tank 2a that regenerates (reduces) to Fe (II), the potential was set to −0.5 V, and electroculturing was performed using the photo-anaerobic electroculturing apparatus 1. FIG. 3 shows the growth of the H-1 strain in the culture tank 2a in which the iron oxidation potential and iron reduction potential are set and in the culture tank 2a that is not regenerated (not electrolyzed) as a control experiment. In the figure,-■-is performed while regenerating (oxidizing) Fe (II) to Fe (III), and-▲-is performed while regenerating (reducing) Fe (III) to Fe (II). And-♦-are those which are not regenerated at all (not electrolyzed). In addition, the vertical axis | shaft of FIG. 3 is the value which measured the light absorbency in 660 nm of the culture medium using the spectrophotometer. This measured value is a value indicating the concentration of the chlorella H-1 strain present in the medium, and the chlorella H-1 strain increases as the absorbance increases. It was confirmed that the growth of the H-1 strain was promoted. In other words, in the Chlorella H-1 strain, growth was promoted as compared with the case where Fe (II) was regenerated (oxidized) to Fe (III) and not regenerated (no electrolysis). From this result, it was confirmed that the chlorella H-1 strain was activated by continuously supplying Fe (III) used as an electron acceptor of photosynthesis, and the growth of the chlorella H-1 strain was promoted. .

It is a figure which shows the structural example of the culture apparatus of the photosynthetic microorganisms concerning this invention. It is a figure which shows the relationship between iron and a photosynthetic system. It is a graph which shows the mode of the growth activity of Chlorella H-1 stock | strain under each condition of no regeneration (no electrolysis) (♦), iron regeneration (oxidation) (■), and iron regeneration (reduction) (▲). It is a figure which shows the concept of the effective utilization of solar energy.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Culture apparatus 2 Electric culture tank 2a Culture tank 2b Counter electrode tank 3 Ion exchange membrane 4 Anode 5 Cathode 6 Potential control apparatus 7 Anaerobic box 8 Medium

Claims (5)

  A sample containing one or more types of photosynthetic microorganisms using Fe (II) or Fe (III) in the photosynthetic reaction is contained in the medium, and Fe (II) contained in the medium while irradiating the medium with light. A method for cultivating a photosynthetic microorganism, wherein the ratio of Fe (II) / Fe (III) to Fe (III) is electrochemically controlled to promote the growth of the photosynthetic microorganism.   The method for culturing photosynthetic microorganisms according to claim 1, wherein the method is carried out under anaerobic conditions.   The method for culturing a photosynthetic microorganism according to claim 1 or 2, wherein the photosynthetic microorganism is a chlorella having an accession number of FERM P-20984.   The method for culturing a photosynthetic microorganism according to claim 1 or 2, wherein the photosynthetic microorganism is Rhodovulum iodosum, Rhodovulum robiginosum, or Rhodopseudomonas palustris strain TIE-1.   An electroculture tank formed of a light transmissive material, an ion exchange membrane that divides the electroculture tank into two layers of a culture tank and a counter electrode tank, an anode provided in the electroculture tank, and a counter electrode tank A cathode provided; a potential control device that controls the potential of the medium in the electric culture tank through the anode and the cathode; and an anaerobic box that keeps the periphery of the electric culture tank in an anaerobic state while transmitting light. A sample containing one or more kinds of photosynthetic microorganisms using Fe (II) or Fe (III) in the photosynthetic reaction in the medium containing at least one of Fe (II) and Fe (III). The ratio of Fe (II) and Fe (III) in the medium is controlled electrochemically while irradiating the medium with light under anaerobic conditions, and the photosynthetic microorganism An apparatus for cultivating photosynthetic microorganisms, characterized by promoting the growth of potato.

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