Strain for converting CO2 into single-cell protein and method for electrosynthesizing single-cell protein by using strain microorganism

Abstract

The invention provides a strain for converting CO2 into a single-cell protein and a method for electrosynthesizing the single-cell protein by using a strain microorganism, and belongs to the technical field of microorganism and green biosynthesis. The preservation number of the strain is CCTCC (China Center For Type Culture Collection) NO: M20232317, and the strain can grow by using CO2 as a unique carbon source and can be used for microbial electrosynthesis of single-cell protein; the invention further relates to an adjustable single-chamber microbial electrosynthesis amplification reactor, the conductive baffle is added between the two electrodes, interference of active oxygen is reduced, the efficiency of a carbon sequestration reaction is improved, the production rate and the protein content of single-cell protein are remarkably improved, the amino acid content of the obtained single-cell protein is kept to be 30% or above, and the yield of the single-cell protein is increased. The concentration of the fructan as an added-value product is about 0.42 mM, and the method has good practicability.

Description

Technical Field

[0001] The invention belongs to the technical field of microorganisms and green biosynthesis, and specifically relates to a strain for converting CO2 into single-cell protein and a method for electrosynthesizing single-cell protein using the strain microorganism. Background Art

[0002] Single-cell protein (SCP) is a protein produced by microbial cells, also known as microbial protein or bacterial protein. Microbial electrosynthesis of single-cell protein is an emerging technology that can use renewable electricity to convert CO2 into edible protein. This process involves the combination of microorganisms and electrochemical reactions. Specifically, some microorganisms can obtain electrons from electrodes and use these electrons to reduce CO2 to organic compounds, such as single-cell protein. In addition, some microorganisms can synergize with other microorganisms through hydrogen transfer to improve the efficiency of electrosynthesis. This microbial electrosynthesis technology is sustainable and environmentally friendly because it can use renewable electricity while converting CO2 into valuable bioproducts. This technology is expected to become an innovative way to produce proteins in the future and provide new solutions to global food security issues.

[0003] Strains with carbon fixation ability for electrosynthetic production of single-cell proteins mainly include hydrogen oxidizing bacteria (HOB), methane oxidizing bacteria (MOB), sulfide-tolerant methane oxidizing bacteria communities, etc. These bacteria directly use energy gases that are insoluble in water, such as hydrogen or methane, to produce single-cell proteins, and it is difficult to grow using electrical energy. The above strains have the following defects: (1) The growth rate is slow under electroculture conditions, resulting in a long single-cell protein (SCP) production cycle and low efficiency; (2) The current process requires the external addition of dangerous gases such as hydrogen and methane, which increases the safety risks of the reaction process. Therefore, it is necessary to screen a new carbon-fixing strain for electrosynthetic production of single-cell proteins.

[0004] In addition, the current reaction devices that cooperate with strains to promote efficient electrosynthesis of SCP have the following defects: (1) The effects of reaction temperature, pH, salinity and other conditions on different strains are different, and the optimization process is complicated; (2) The conductivity, stability and catalytic performance of current electrode materials still need to be improved; (3) The metabolic pathways and interactions of microorganisms are not yet fully understood; (4) Factors such as equipment investment, operating costs and product market demand affect the overall economic feasibility, and laboratory-scale success is difficult to transform into industrial large-scale application production. Therefore, it is also necessary to design an efficient and safe microbial electrosynthesis reactor for the production of single-cell proteins. Summary of the invention

[0005] In view of some deficiencies in the prior art, the present invention provides a strain for converting CO2 into single-cell protein and a method for electrosynthesizing single-cell protein using the strain. The strain is deposited in the China Center for Type Culture Collection with a deposit number of CCTCC NO:M 20232317, a deposit date of November 24, 2023, a deposit address in Wuhan, China, and a taxonomic name of Microbacterium sp.WT-1. The strain can grow using CO2 as the sole carbon source and can be used for electrosynthesis of single-cell protein by microorganisms. The present invention also relates to an adjustable single-chamber microbial electrosynthesis amplification reactor, which reduces the interference of active oxygen by adding a conductive baffle between two electrodes, improves the efficiency of the carbon fixation reaction, and significantly improves the production rate of single-cell protein (1OD 600 / d) and protein content (65%), the amino acid content of the obtained single-cell protein is maintained above 30%, and the concentration of the value-added product fructan is about 0.42mM, which has good practicality.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical means:

[0007] The present invention first provides a strain for converting CO2 into single-cell protein. The strain is deposited in the China Center for Type Culture Collection, with a deposit number of CCTCC NO:M 20232317, a deposit date of November 24, 2023, a deposit address of Wuhan, China, and a taxonomic name of Microbacterium sp.WT-1.

[0008] Preferably, the strain that converts CO2 into single-cell protein is a Gram-positive bacterium, and its 16S rRNA gene sequence is shown in SEQ ID No:1.

[0009] The present invention also provides a microbial agent, which includes the above-mentioned strain that converts CO2 into single-cell protein.

[0010] The present invention also provides the use of the above-mentioned strain or microbial agent for converting CO2 into single-cell protein in microbial electrosynthesis of single-cell protein.

[0011] The present invention also provides an electrochemical reactor for electrosynthesis of single-cell protein by microorganisms, the electrochemical reactor comprising: a single-chamber electrolytic cell; a pH meter 4 is provided in the middle of a reactor cover 1 of the single-chamber electrolytic cell, and a CO2 inlet 2, a cathode 3, an NH4 + Liquid sample injection port 5 and anode 6;

[0012] An anode chamber 7 is provided outside the bottom of the anode 6, and the anode chamber 7 is formed by a conductive baffle and a side wall partition of the single-chamber electrolytic cell;

[0013] The cathode 3 is submerged below the electrolyte surface and is 2 cm away from the bottom of the reactor; the distance between the cathode 3 and the anode 6 is 4 cm.

[0014] Preferably, the reactor cover outside the pH meter 4 is stepped to facilitate the insertion of the pH meter 4 .

[0015] Preferably, the cathode 3 comprises any one of pure carbon cloth, carbon cloth modified with Co-P, stainless steel mesh, and stainless steel mesh modified with Co-P;

[0016] The anode 6 includes any one of pure carbon cloth, carbon cloth modified with CoPi, ruthenium-iridium electrode, and ruthenium-iridium electrode modified with CoPi.

[0017] The present invention also provides a method for converting CO2 into electrosynthetic single-cell protein by microorganisms using the electrochemical reactor, the method comprising:

[0018] The bacterial solution of the above-mentioned strain that converts CO2 into single-cell protein is inoculated to the outside of the anode chamber 7, and the NH4 + Add electrolyte to the liquid sample port 5, connect the CO2 inlet 2 to the CO2 cylinder through the gas pipe, turn on the voltage in the power control system, and use the pH meter 4 to detect and record the pH change of the fermentation liquid at regular intervals and extract NH4 + Supplement NH 4+ Liquid is used to regulate the pH balance of the reaction system of the reactor; samples are taken to record the growth of the strain.

[0019] Preferably, the final concentration of the bacterial solution is OD 600 =0.2;

[0020] The electrolyte includes an inorganic salt culture medium and 25 mM NaHCO3, wherein the components of the inorganic salt culture medium include: 6.74 g NaHPO4·7H2O, 1.5 g KH2PO4, 0.167 g (NH4)2SO4, 80 mg MgSO4·7H2O, 1 mg CaSO4·2H2O, 0.56 mg NiSO4·7H2O and 0.4 mg ferric citrate;

[0021] The concentration of CO2 introduced into CO2 inlet 2 is 20-30 mM;

[0022] The voltage in the control system is 2.0V;

[0023] The pH balance is as follows: adjusting the pH value to 6.8-7.0.

[0024] Preferably, the concentration of CO2 introduced into the CO2 inlet 2 is 25 mM.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention adopts a microbial electrosynthesis method and utilizes in-situ electrode energy supply to promote the growth of specific cells for carbon fixation, thereby obtaining SCP more efficiently, safely, and cheaply. In-situ electrode energy supply means that during the microbial electrosynthesis process, the electrode directly provides electrical energy to the microorganism to drive the CO2 reduction reaction. This energy supply method converts the electric current into an energy form that can be used by the microorganism through direct contact between the electrode and the electrolyte solution, reduces the dependence on external energy sources, simplifies the reaction system, and improves the overall stability of the system. At the same time, in-situ energy supply helps to regulate the reaction conditions, thereby increasing the yield and selectivity of specific value-added products, which provides a new way to improve the efficiency and product quality of microbial electrosynthesis systems.

[0027] (2) The strain for converting CO2 to single-cell protein and the method for electrosynthesizing single-cell protein using the strain in the present invention solve the problems of insufficient bacterial growth efficiency, safety issues, high equipment and operating costs, and low carbon fixation efficiency in the prior art. The present invention designs a new type of fully decomposed water electrode and its electrochemical system, and uses electrical energy to drive the strain to grow in situ using CO2 as the only carbon source, thereby screening a Gram-positive strain with a fast growth rate under electrosynthesis conditions. At the same time, the reaction conditions are optimized, and an adjustable single-chamber microbial electrosynthesis amplification reactor is designed. By adding a conductive baffle between the two electrodes, the interference of active oxygen is reduced, the efficiency of the carbon fixation reaction is improved, and the production rate of single-cell protein is significantly increased (1OD 600 / d) and protein content (65%).

[0028] (3) The method of microbial electrosynthesis of single-cell protein described in the present invention avoids external hydrogen supply, reduces process risks, and improves overall production safety. This method can effectively increase the yield of protein and fructan. Under optimal conditions, the amino acid content of single-cell protein can reach more than 30%, and the fructan concentration can reach 0.42±0.01mM. In addition, the reactor system described in the present invention is stable and easy to control. The use of conductive baffles avoids the interference of by-products on the reaction, improves the carbon fixation efficiency, and achieves a higher SCP production rate. The reaction system described in the present invention relies on direct energy supply from electrodes to achieve efficient fixation of CO2. It has the advantages of low cost and environmental protection, and is expected to provide important technical support for future food safety and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The constant potential OD of the strain for converting CO2 into single cell protein of the present invention and the traditional hydrogen oxidizing bacteria Cupriavidusnecator 600 Enrichment growth curve.

[0030] Figure 2 (a) is the OD of different cathodes when the anodes are all pure carbon cloth 600 Enrichment growth curve; (b) is the OD of different anodes at the optimal cathode 600 Enrichment growth curve.

[0031] Figure 3 This is a graph of cell dry weight and protein concentration of different cathodes when the anode is ordinary carbon cloth.

[0032] Figure 4 Schematic diagram of the designed controllable reactor (a) and schematic diagram of the reactor cover (b).

[0033] Figure 5 It is an analysis chart of amino acid composition and content.

[0034] Figure 6 This is a graph showing the fructose HPLC detection content after hydrolysis of different cathode fermentation liquids when the anode is ordinary carbon cloth.

[0035] In the figure, 1-reactor cover; 2-CO2 inlet; 3-cathode; 4-pH meter probe; 5-NH4 + Liquid sample addition port; 6- anode; 7- anode chamber. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto. The following embodiments are for a clear and complete description of the technical solution of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0037] Unless otherwise defined, technical or scientific terms used herein shall have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs.

[0038] The components of the inorganic salt culture medium involved in the following examples are: 6.74g NaHPO4·7H2O, 1.5g KH2PO4, 0.167g (NH4)2SO4, 80mg MgSO4·7H2O, 1mg CaSO4·2H2O, 0.56mg NiSO4·7H2O and 0.4mg ferric citrate (the initial pH of the culture medium was adjusted to 6.8-7.0 in advance by 1M HCl).

[0039] LB solid medium ( / L) composition: 10 g NaCl; 10 g tryptone; 5 g yeast powder; 15 g agar powder, pH = 6.8.

[0040] Example 1: Construction of an electrochemical reactor for microbial electrosynthesis of single-cell protein and screening of strains that convert CO2 to single-cell protein

[0041] In this example, an electrochemical reactor for electrosynthesis of single-cell protein by microorganisms was first constructed. Then, soil blocks from farmland near Jiangsu University were used as samples. Based on the constructed electrochemical reactor for electrosynthesis of single-cell protein by microorganisms, a strain capable of producing single-cell protein using CO2 as the sole carbon source was separated and purified and strains were screened. The specific steps are as follows:

[0042] S1. Construction of an electrochemical reactor for microbial electrosynthesis of single-cell proteins:

[0043] S11. Pretreatment of carbon cloth electrode:

[0044] The carbon cloth was soaked in anhydrous acetone for 8 hours, and then soaked in 3 mol / L HCl solution for 12 hours. After soaking, it was repeatedly ultrasonically cleaned with ultrapure water until its pH was 7, and then dried to obtain the pretreated carbon cloth. The pretreated carbon cloth was cut into 1*2 cm 2 The carbon cloth was connected with a 10-12 cm titanium wire as a conductor to obtain a carbon cloth electrode.

[0045] S12. Preparation of Co-P modified carbon cloth electrode:

[0046] A 50mL single-chamber electrolytic cell was used, and a three-electrode system was adopted, with AgCl as the reference electrode, Pt wire as the auxiliary electrode, and carbon cloth electrode as the working electrode. About 30mL of electrolyte was used to submerge the working electrode. The electrode was modified by electrodeposition, where the electrolyte composition was: 0.15M H3BO3, 0.1M NaCl, 0.33M Na2H2PO2, and 0.2M CoCl2. Finally, it was connected to the electrochemical workstation CHI 660, and modified for about 30 minutes in the constant potential mode of -1.2V vs.AgCl. When there was a layer of obvious silver-white metal coating on the carbon cloth, the Co-P modified carbon cloth electrode was obtained.

[0047] S13. Construction of an electrochemical reactor for electrosynthesis of single-cell proteins by microorganisms:

[0048] The electrochemical reactor for microbial electrosynthesis of single-cell protein is a 50mL single-chamber electrolyzer, which adopts a two-electrode system, wherein the cathode is a Co-P modified carbon cloth electrode, and the anode is a carbon cloth electrode without any modification. The distance between the two electrodes is 4cm, and an inorganic salt culture medium is used as the electrolyte. The working volume is 40mL, and it is connected to an electrochemical workstation CS Studio, and 1.23V is set in the constant voltage mode to obtain the electrochemical reactor for microbial electrosynthesis of single-cell protein.

[0049] S14. Validation of electrochemical reactor for microbial electrosynthesis of single-cell protein:

[0050] In this step, the traditional hydrogen oxidizing bacteria Ralstonia Cupriavidus necator H16 (ATCC17699) is used to verify the feasibility of the electrochemical reactor for microbial electrosynthesis of single-cell protein constructed in step S13. The specific steps are as follows:

[0051] Inoculate Cupriavidus necator H16 into liquid LB in a glycerol tube and culture overnight at 30°C for 12 hours, then wash three times with PBS buffer at 6000rpm, 5min centrifugation to obtain bacterial sludge. Add bacterial sludge to the electrolytic cell of the electrochemical reactor for microbial electrosynthesis of single-cell protein constructed in step S13, aspirate evenly with a pipette, and add 25mM NaHCO3 to the electrolyte. Connect the cathode and anode to the electrochemical workstation CS Studio, set 1.23V in constant voltage mode, and the speed of the magnetic stirrer is 120rpm. Observe the OD of the strain within one week. 600 Finally, it was found that Cupriavidus necatorH16 can grow with CO2 as the only carbon source in the above system.

[0052] This indicates that the electrode and the electrochemical reactor for microbial electrosynthesis of single-cell protein constructed by the present invention can be used for microbial electrosynthesis of single-cell protein.

[0053] S2. Screening of strains that convert CO2 into single-cell protein:

[0054] S21. Sample collection:

[0055] Soil blocks collected from a farmland near Jiangsu University were used as samples. After loose soil blocks were shaken off, the samples were ground into powder using a mortar and pestle, and then dissolved in deionized water to obtain the collected bacterial liquid samples.

[0056] S22. Strain enrichment:

[0057] Add 10 mL of collected bacterial sample and 30 mL of inorganic salt culture medium to the electrochemical reactor for microbial electrosynthesis of single-cell protein constructed in step S13, and add 25 mM NaHCO3 as a CO2 source. The speed of the magnetic stirrer is 120 rpm. Use a DC regulated power supply, connect the anode and cathode, set a constant voltage of 1.23 V, and observe the pH changes and OD changes of the mixed bacteria in the reactor within one week. 600 Growth, it was found that the pH of the reactor would slightly decrease, OD 600 There is an obvious increase, and electric fermentation liquid is obtained.

[0058] S23. Strain isolation and purification:

[0059] The electro-fermentation liquid obtained in S22 was gradiently diluted and spread on LB medium plates, inverted and cultured at room temperature. When obvious colonies grew on the plates, single colonies of different morphologies were picked up and streaked onto LB medium plates in turn. After observing the growth of the colonies, the colonies were picked up and transferred to LB liquid culture medium, inverted and cultured at room temperature to obtain a bacterial liquid containing single colonies of different types.

[0060] S24. Bacteria screening:

[0061] The bacterial liquid of different single bacteria in S23 was centrifuged and resuspended and placed in the electrolytic cell culture device with continuous hydrogen flow in turn to observe the OD of different single bacteria in the reactor within one week. 600 Growth. Repeat step S14 and culture for one week, then apply gradient dilutions to LB medium plates, invert and culture at room temperature, and compare with the colonies screened for the first time after obvious colonies grow on the plates. Select colonies with similar morphology to the first screened colonies and streak them on LB medium plates for continuous culture. Purify each colony more than three times to obtain strains with the ability to electrosynthesize single-cell proteins, transfer them to 30% glycerol cryovials, and store at -80°C for later use.

[0062] S25. Determination of cell dry weight and protein concentration:

[0063] The pure bacterial solution obtained by inoculating the S24 glycerol tube was repeated in step S14 to divide the electrocatalyzed fermentation solution into two parts: one part was washed by centrifugation at 6000 rpm for 5 minutes at room temperature, and then freeze-dried and weighed on an electronic balance to obtain the cell dry weight; the other part was ultrasonically disrupted (ultrasound on for 6 seconds, ultrasound off for 6 seconds, power 30%), and then centrifuged to obtain the supernatant, and the protein concentration was measured on an ELISA instrument using the BCA method (refer to the instructions for the kit of Bio-Tech Company). The results are shown in the attached figure. Figure 3 As shown, the protein concentration and cell dry weight ratio were maintained above 50%.

[0064] S26. Identification of bacterial species:

[0065] Combined with the conclusions of steps S24 and S25 and the attached Figure 1The dominant strain was compared with the traditional Cupriavidus necator H16 to determine that the dominant strain was Strain 1 with the fastest growth rate; the bacterial solution of the dominant strain was verified by PCR electrophoresis, and the PCR amplification product was sent to Shanghai Sangon Biotechnology Co., Ltd. for 16sRNA sequencing analysis and strain identification. After sequencing, the 16sRNA of the dominant strain was shown in SEQ ID No: 1. The strain sequence obtained by sequencing was compared with the Blast sequence on NCBI, and it was found that the strain belonged to Microbacterium sp. WT-1. After streaking and inoculating on the slant test tube to grow a single colony, it was sent to the China Center for Type Culture Collection, with a deposit number of CCTCC NO: M 20232317, a deposit date of November 24, 2023, a deposit address of Wuhan, China, and a taxonomic name of Microbacterium sp. WT-1.

[0066] SEQ ID No:1

[0067]

[0068] Example 2: Optimization of electrochemical reactor structure and conditions for microbial electrosynthesis of single-cell protein

[0069] This example optimizes the electrochemical reactor for electrosynthesis of single-cell protein by microorganisms constructed in Example 1. The optimized electrochemical reactor for electrosynthesis of single-cell protein by microorganisms is shown in the attached figure. Figure 4 As shown, the specific optimization is as follows:

[0070] (1) Reactor design:

[0071] The MES reactor is made of acrylic sheet, with a total volume of 1L and a working volume of 800mL. Figure 4 As shown on the left, the electrochemical reactor comprises: a single-chamber electrolyzer; a pH meter 4 is provided in the middle of the reactor cover 1 of the single-chamber electrolyzer, and a CO2 inlet 2, a cathode 3, an NH4 + Liquid injection port 5 and anode 6; an anode chamber 7 is provided on the outer side of the bottom of the anode 6, and the anode chamber 7 is formed by a conductive baffle and the side wall partition of the single-chamber electrolytic cell; the cathode 3 is submerged to the lower layer of the liquid surface, and is 2 cm away from the bottom of the reactor; the distance between the cathode 3 and the anode 6 is 4 cm, which helps to accelerate the strain's use of electrical energy, while reducing the generation of active oxygen on the electrode, ensuring the activity of the strain during long-term reactor operation. During the implementation process, the reactor cover on the outside of the pH meter 4 is stepped inside to facilitate the insertion of the pH meter 4. Figure 4 The right side is a top view of the reactor, mainly the reactor cover, where ports 2, 3, 4, 5, and 6 are connected to the CO2 inlet, cathode, pH meter socket, and NH4 + The liquid sample addition port and the anode correspond to each other and their sizes remain consistent.

[0072] (2) Voltage optimization:

[0073] Under certain conditions, the higher the applied voltage, the greater the current density in the circuit, and the higher the electrical energy conversion rate, which can accelerate the conversion of CO2 to SCP. This step optimizes the voltage of the electrochemical reactor for microbial electrosynthesis of single-cell protein. The specific steps are as follows:

[0074] The dominant strain obtained in Example 1S26 was inoculated into liquid LB and cultured overnight at 30°C for 12 h. After washing three times by centrifugation at 6000 rpm for 5 min with PBS buffer, a final concentration of OD 600= 0.2 bacterial solution, aspirate evenly with a pipette, and add 25mM NaHCO3 (filter sterilized) to the inorganic salt medium. Connect the anode and cathode to a DC voltage regulator, set to 2.0V in the constant voltage mode, and the speed of the magnetic stirrer is 120rpm. After one week, measure the strain OD at the potential of 1.23V and 2.0V respectively. 600 Growth conditions.

[0075] From the attached Figure 2 (a) and Figure 1 It can be seen that when the same electrode is used, the OD of the strain with a voltage of 2.0 V is higher than that of the strain with a voltage of 1.23 V. 600 The growth rate is about 0.5 faster. This shows that applying overpotential under certain conditions is beneficial to the growth of the strain.

[0076] (3) Optimization of cathode and anode electrodes:

[0077] The conventional cathode for hydrogen evolution is stainless steel (referred to as SS). In this step, the anode is a carbon cloth electrode (referred to as CC). Four parallel controls are set up, and the cathodes are CC, CC modified with Co-P (referred to as CC@Co-P), SS, and SS modified with Co-P (referred to as SS@Co-P). The method for modifying Co-P is as shown in Example 1, and only the electrolyte composition is adjusted: 10mM Co(NO3)2 and 0.1M methylphosphonate (MePi) buffer with pH=8, and the modification is carried out for about 30min in the constant potential mode of 0.85V vs.AgCl.

[0078] The final inoculation concentration OD in the electrochemical reactor for microbial electrosynthesis of single-cell protein was 600 =0.2, the dominant strain obtained in Example 1S26 was subjected to constant voltage catalysis at 2.0 V for 7 days, and the OD values ​​of the four groups of strains were measured respectively. 600 Growth conditions. Figure 2 As can be seen in (a), the strain with SS@Co-P as cathode has the best growth condition, OD 600 is about 4. Therefore, SS@Co-P is the best choice for the cathode.

[0079] According to the above conclusions, SS@Co-P is the best cathode. The electrode material ruthenium-iridium electrode commonly used in electrochemical oxidation reactions is selected to set up four groups of parallel controls to optimize the anode. The anodes are CC, CC modified with CoPi, ruthenium-iridium, and ruthenium-iridium modified with CoPi. The initial and final concentrations of the reactor inoculation are OD 600 = 0.2, and the OD values ​​of the four groups of strains were measured after catalysis at 2.0 V for 7 days. 600 Growth conditions. Figure 2As can be seen in (b), the strain with Ruthenium-Iridium@CoPi has the best growth condition, OD 600 is about 6.5. Therefore, RutheniumIridium@CoPi is the best choice for the anode.

[0080] In summary, after optimization, the best cathode is SS@Co-P, the best anode is rutheniumiridium@CoPi, and the electrocatalytic potential is 2.0V.

[0081] Example 3. Analysis of amino acid composition and fructan in single-cell protein synthesized by microorganisms

[0082] In this example, the amino acid composition and fructan content of the single-cell protein synthesized by microorganisms were respectively determined to investigate the nutritional value and added value of the obtained single-cell protein. The specific steps are as follows:

[0083] S1. Determination of amino acids:

[0084] The single cell protein was prepared using the optimal conditions in Example 2 and the strain screened in Example 1 with CO2 as the carbon source. The fermentation broth obtained after electrocatalysis was centrifuged twice at 6000 rpm, 5 min (4°C), the supernatant was discarded, and the precipitate was centrifuged and washed twice with 4 volumes of pre-cooled anhydrous ethanol at 12000 rpm, 10 min (4°C). The obtained precipitate was dissolved in deionized water, dialyzed with a dialysis membrane (MWCO 14000Da) at 4°C for 72 hours, the magnetic stirrer speed was 200 rpm, and the dialyzed sample was freeze-dried.

[0085] The freeze-dried sample was ground and crushed, and then 10 mL to 15 mL of 6 M HCI solution was added to dissolve it according to the protein content. The sample was injected into the amino acid analyzer using a JJG 1064-2011 amino acid analyzer with a sulfonic acid cationic resin column. The concentration of amino acids in the sample solution was calculated by the peak area using the external standard method at a detection wavelength of 570 nm.

[0086] The test results are as attached Figure 5 As shown in the figure, it can be seen that among the essential amino acids in the final amino acid composition, only tryptophan was not detected, and the non-essential amino acids asparagine, glutamine and cysteine ​​were not detected, and the amino acid concentration was maintained above 30%. Therefore, the amino acid content of the single-cell protein prepared by the method of the present invention is at a normal level.

[0087] S2. Analysis and determination of fructan:

[0088] Since fructosan is a polymer of β-D-furanose, it is a general term for polysaccharides generated by fructose polymerization. It cannot be directly measured and needs to be hydrolyzed into monomeric fructose for determination by high performance liquid chromatography. The fermentation broth obtained after electrocatalysis in step S1 of this embodiment is first ultrasonically broken (ultrasound on 6s, ultrasound off 6s, power 30%), and then 1:1 volume of 6M HCl is added to react in a water bath at 100°C for 15min. Take 300μL of the hydrolyzed sample solution and add 30uL 1M H2SO4 to terminate the reaction, then centrifuge at 12000rpm, 10min at room temperature to take the supernatant, and filter with a 0.22μm water system membrane and then use a pipette to draw about 180μL and put it into the injection bottle.

[0089] The selected instrument is Shimadzu HPLC, the pump model is LC-20AD, and the chromatographic column is HPX-87H ( 300mm×7.8mm), the mobile phase was 4mmol / L H2SO4. RID-10A detector was used, the automatic injection mode was set, the injection volume was 20μL each time, the analysis was carried out at a flow rate of 0.4mL / min and a column temperature of 50℃. The test results are shown in the attached Figure 6 described.

[0090] As can be seen from the figure, the optimal fructose content at cathode calculated according to the standard curve is about 0.42±0.01mM.

[0091] In summary, the present invention provides a strain for converting CO2 into single-cell protein and a method for electrosynthesizing single-cell protein using the strain. The strain is deposited in the China Center for Type Culture Collection with a deposit number of CCTCCNO:M 20232317, a deposit date of November 24, 2023, a deposit address of Wuhan, China, and a taxonomic name of Microbacterium sp.WT; the strain can grow using CO2 as the sole carbon source and can be used for electrosynthesis of single-cell protein by microorganisms; the present invention also relates to an adjustable single-chamber microbial electrosynthesis amplification reactor, which reduces the interference of active oxygen by adding a conductive baffle between two electrodes, improves the efficiency of the carbon fixation reaction, and significantly improves the production rate of single-cell protein (1OD 600 / d) and protein content (65%), the amino acid content of the obtained single-cell protein is maintained at more than 30%, and the concentration of the value-added product fructan is about 0.42mM, which has good practicality. The single-cell protein obtained by the present invention has the advantages of high yield and rich nutritional value of ingredients. The single-cell protein is generated by carbon fixation using an in-situ electrosynthesis method, which avoids the danger of traditional hydrogenophilic autotrophic bacteria under high-pressure hydrogen supply, and has the advantages of low energy consumption, environmental protection and safety.

[0092] The embodiments are preferred implementations of the present invention, but the present invention is not limited to the above-mentioned implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essential content of the present invention belong to the protection scope of the present invention.

Claims

1. A strain for converting CO2 into single-cell protein, characterized in that: The strain is deposited in the China Center for Type Culture Collection, with a deposit number of CCTCC NO:M 20232317, a deposit date of November 24, 2023, a deposit address of Wuhan, China, and a taxonomic name of Microbacterium sp.WT-1.

2. The strain for converting CO2 to single-cell protein according to claim 1, characterized in that: The strain for converting CO2 into single-cell protein is a Gram-positive bacterium, and its 16S rRNA gene sequence is shown in SEQ ID No:

1.

3. A microbial agent, characterized in that: The microbial agent includes the strain for converting CO2 into single-cell protein as described in claim 1.

4. Use of the strain for converting CO2 into single-cell protein according to claim 1 or the microbial agent according to claim 2 in microbial electrosynthesis of single-cell protein.

5. An electrochemical reactor for electrosynthesis of single-cell protein by microorganisms, characterized in that: The electrochemical reactor comprises: a single-chamber electrolytic cell; a pH meter (4) is provided in the middle of a reactor cover (1) of the single-chamber electrolytic cell, and a CO2 inlet (2), a cathode (3), an NH4 + A liquid sample addition port (5) and an anode (6); An anode chamber (7) is provided outside the bottom of the anode (6), and the anode chamber (7) is formed by a conductive baffle and a side wall partition of the single-chamber electrolytic cell; The cathode (3) is submerged below the electrolyte surface and is 2 cm away from the bottom of the reactor; the distance between the cathode (3) and the anode (6) is 4 cm.

6. The electrochemical reactor for electrosynthesis of single-cell protein by microorganisms according to claim 5, characterized in that: The reactor cover outside the pH meter (4) is in an inner stepped manner, which is convenient for inserting the pH meter (4).

7. The electrochemical reactor for electrosynthesis of single-cell protein by microorganisms according to claim 5, characterized in that: The cathode (3) comprises any one of pure carbon cloth, carbon cloth modified with Co-P, stainless steel mesh, and stainless steel mesh modified with Co-P; The anode (6) comprises any one of pure carbon cloth, carbon cloth modified with CoPi, a ruthenium-iridium electrode, and a ruthenium-iridium electrode modified with CoPi.

8. The method for converting CO2 into microbial electrosynthesis of single-cell protein by electrochemical reactor according to claim 5, characterized in that: The method comprises: The bacterial liquid of the strain for converting CO2 into single cell protein according to claim 1 is inoculated to the outside of the anode chamber (7), and the NH 4+ The electrolyte is added to the liquid sample port (5), the CO2 inlet (2) is connected to the CO2 cylinder through the gas pipe, the voltage in the power control system is turned on, and the pH change of the fermentation liquid is detected and recorded with a pH meter (4) at regular intervals and the NH4 + Add NH4 to the liquid sample port (5) + Liquid is used to regulate the pH balance of the reaction system of the reactor; samples are taken to record the growth of the strain.

9. The method according to claim 8, characterized in that The final concentration of the bacterial solution is OD 600 =0.2; The electrolyte includes an inorganic salt culture medium and 25 mM NaHCO3, wherein the components of the inorganic salt culture medium include: 6.74 g NaHPO4·7H2O, 1.5 g KH2PO4, 0.167 g (NH4)2SO4, 80 mg MgSO4·7H2O, 1 mg CaSO4·2H2O, 0.56 mg NiSO4·7H2O and 0.4 mg ferric citrate; The voltage in the control system is 2.0V; The pH balance is as follows: adjusting the pH value to 6.8-7.

0.

10. The method according to claim 9, characterized in that The concentration of CO2 introduced into the CO2 inlet (2) is 20-30 mM.

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