Construction and Application of Engineered Strain of Escherichia Coli for Producing Malic Acid by Fixing CO2

Abstract

The disclosure discloses construction and application of an engineered strain of E. coli for producing malic acid by fixing CO.sub.2, and belongs to the field of fermentation. The engineered strain is obtained by performing genetic engineering transformation on Escherichia coli MG1655; the genetic engineering transformation includes knocking out a fumarate reductase gene, a fumarase gene, a lactate dehydrogenase gene and an alcohol dehydrogenase gene and freely overexpressing a formate dehydrogenase, an acetyl coenzyme A synthetase, an acylated acetaldehyde dehydrogenase, a formaldehyde lyase, a dihydroxyacetone kinase, a malic enzyme and a phosphite oxidoreductase to obtain a strain GH0407. The strain is used for producing malic acid by fermentation, anaerobic fermentation is performed for 72 hours with CO.sub.2 and glucose as a co-substrate, the production of malic acid reaches 39 g/L, the yield is 1.53 mol/mol, and accumulation of malic acid in the original strain is not achieved.

Claims

1. An engineered strain of E. coli for producing malic acid by fixing CO.sub.2, wherein a fumarate reductase gene (frdBC), a fumarase gene (fumB), a lactate dehydrogenase gene (ldhA) and an alcohol dehydrogenase gene (adhE) of the engineered strain of E. coli are knocked out, and a formate dehydrogenase (FDH), an acetyl coenzyme A synthetase (ACS), an acylated acetaldehyde dehydrogenase (ACDH), a formaldehyde lyase (FLS), a dihydroxyacetone kinase (DHAP), a malic enzyme (ME) and a phosphite oxidoreductase (PTXD) are overexpressed.

2. The engineered strain of E. coli for producing malic acid by fixing CO.sub.2 according to claim 1, wherein the formate dehydrogenase, the acetyl coenzyme A synthetase, the acylated acetaldehyde dehydrogenase, the formaldehyde lyase and the dihydroxyacetone kinase are gradually ligated to a vector by isocaudamer assembly for overexpression.

3. The engineered strain of E. coli for producing malic acid by fixing CO.sub.2 according to claim 2, wherein the engineered strain of E. coli is obtained by using Escherichia coli MG1655 as a host.

4. The engineered strain of E. coli for producing malic acid by fixing CO.sub.2 according to claim 3, wherein a nucleotide sequence of the vector is set forth in SEQ ID NO. 5.

5. The engineered strain of E. coli for producing malic acid by fixing CO.sub.2 according to claim 4, wherein a malic enzyme gene and a phosphite oxidoreductase gene are ligated to the vector by isocaudamer assembly for overexpression.

6. The engineered strain of E. coli for producing malic acid by fixing CO.sub.2 according to claim 5, wherein a nucleotide sequence of the vector is set forth in SEQ ID NO. 6.

7. The engineered strain of E. coli for producing malic acid by fixing CO.sub.2 according to claim 1, wherein a nucleotide sequence of the fumarate reductase gene is set forth in SEQ ID NO. 7 or SEQ ID NO. 8, a nucleotide sequence of the fumarase gene is set forth in SEQ ID NO. 9, a nucleotide sequence of the lactate dehydrogenase gene is set forth in SEQ ID NO. 10, a nucleotide sequence of the alcohol dehydrogenase gene is set forth in SEQ ID NO. 11, a nucleotide sequence of a formate dehydrogenase gene is set forth in SEQ ID NO. 12, a nucleotide sequence of an acetyl coenzyme A synthetase gene is set forth in SEQ ID NO. 13, a gene sequence of the acylated acetaldehyde dehydrogenase is set forth in SEQ ID NO. 1, a gene sequence of the formaldehyde lyase is set forth in SEQ ID NO. 2, a gene sequence of the dihydroxyacetone kinase is set forth in SEQ ID NO. 3, a nucleotide sequence of the malic enzyme gene is set forth in SEQ ID NO. 14, and a nucleotide sequence of the phosphite oxidoreductase gene is set forth in SEQ ID NO. 4.

8. A method for producing malic acid, comprising fermenting the engineered strain of E. coli according to claim 7 in a fermentation culture system comprising glucose.

9. The method according to claim 8, wherein fermentation is performed at 30-37° C. for lasting at least 24 hours.

10. The method according to claim 9, wherein pH is controlled to be 6.5-7.0 in a fermentation process.

11. The method according to claim 8, wherein the engineered strain of E. coli is activated and then subjected to aerobic culture for 12-18 hours at a temperature of 30-37° C. and a rotation speed of 700-800 rpm under an oxygen ventilation rate of 0.8-1.2 vvm and pH of 6.5-7.0; then, the oxygen ventilation rate is adjusted to 0 vvm, the rotation speed is adjusted to 180-200 rpm, nitrogen is introduced at a speed of 1 vvm for 10-20 minutes, and the engineered strain of E. coli is fermented for 60-80 hours under anaerobic conditions and neutral pH.

12. The method according to claim 8, wherein a fermentation culture medium for fermentation comprises 40-50 g/L of glucose, 20-50 mM of Na.sub.2HPO.sub.3.5H.sub.2O, 30-50 mM of KHCO.sub.3, 15.11 g/L of Na.sub.2HPO.sub.4.12H.sub.2O, 3 g/L of KH.sub.2PO.sub.4, 1 g/L of NH.sub.4Cl and 0.5 g/L of NaCl, and 1 L of the culture medium contains 1 mL of a trace element solution; the trace element solution is prepared by dissolving 2.4 g/L of FeCl.sub.3.6H.sub.2O, 0.3 g/L of CoCl.sub.2.6H.sub.2O, 0.15 g/L of CuCl.sub.2, 0.3 g/L of ZnCl.sub.2.4H.sub.2O, 0.3 g/L of NaMnO.sub.4, 0.075 g/L of H.sub.3BO.sub.3 and 0.495 g/L of MnCl.sub.2.4H.sub.2O in 0.1 M HCl.

13. The method according to claim 11, wherein the fermentation culture medium for fermentation comprises 40-50 g/L of glucose, 20-50 mM of Na.sub.2HPO.sub.3.5H.sub.2O, 30-50 mM of KHCO.sub.3, 15.11 g/L of Na.sub.2HPO.sub.4.12H.sub.2O, 3 g/L of KH.sub.2PO.sub.4, 1 g/L of NH.sub.4Cl and 0.5 g/L of NaCl, and 1 L of the culture medium contains 1 mL of the trace element solution; the trace element solution is prepared by dissolving 2.4 g/L of FeCl.sub.3.6H.sub.2O, 0.3 g/L of CoCl.sub.2.6H.sub.2O, 0.15 g/L of CuCl.sub.2, 0.3 g/L of ZnCl.sub.2.4H.sub.2O, 0.3 g/L of NaMnO.sub.4, 0.075 g/L of H.sub.3BO.sub.3 and 0.495 g/L of MnCl.sub.2.4H.sub.2O in 0.1 M HCl.

Description

BRIEF DESCRIPTION OF FIGURES

[0024] FIG. 1 shows construction of a synthetic path of malic acid by fixing CO.sub.2 in an engineered strain of E. coli.

[0025] FIG. 2 is an frdBC gene knockout verification electrophoretogram [lanes 1-18 all refer to transformants in which an frdBC gene is successfully knocked out, lane 19 (marked “+”) refers to colony PCR results of wild-type E. coli, and lane 19 (marked “−”) refers to a no-treatment control group].

[0026] FIG. 3 is an fumB gene knockout verification electrophoretogram [lanes 1-11 and 13-14 all refer to transformants in which an fumB gene is successfully knocked out, lanes 12 and 15-16 are transformants in which the fumB gene is not successfully knocked out, lane 17 (marked “+”) refers to colony PCR results of wild-type E. coli, and lane 18 (marked “−”) refers to a no-treatment control group].

[0027] FIG. 4 is an ldhA gene knockout verification electrophoretogram [lane 3 is transformants in which an ldhA gene is not successfully knocked out, and lanes 8-10 refer to transformants in which the ldhA gene is successfully knocked out].

[0028] FIG. 5 is an adhE gene knockout verification electrophoretogram [lanes 1-4, 6-14 and 16 all refer to transformants in which an adhE gene is successfully knocked out, lane 17 (marked “+”) refers to colony PCR results of wild-type E. coli, and lane 18 (marked “−”) refers to a no-treatment control group].

[0029] FIG. 6 is a diagram of a recombinant plasmid pER-CF5A.

[0030] FIG. 7 is a diagram of a recombinant plasmid pCDR-ME-PTXD.

[0031] FIG. 8 shows a production-time curve of malic acid produced by fermentation of E. coli.

[0032] FIG. 9 shows the yield of malic acid produced by fermentation of E. coli.

DETAILED DESCRIPTION

[0033] A detection method of malic acid (high performance liquid chromatography conditions): Aminex HPX-87H (7.8*300 mm) is used as a chromatographic column, a mobile phase includes 5 mM of H.sub.2SO.sub.4, the column temperature is 35° C., the detection wavelength is 210 nm, the injection volume is 10 μl, and the flow rate is 0.6 ml/min.

[0034] Purchase sources of commercial plasmid products: pKD4, pKD46 and pCP20 plasmids are purchased from BioVector NTCC. A pER plasmid is obtained by transforming a promoter region of pETM6 (purchased from addgene, #49795), and a pCDR plasmid is obtained by transforming a promoter region of pCDM4 (purchased from addgene, #49796).

[0035] Detection and calculation methods of a CO.sub.2 fixation rate: (1) detection method: first, E. coli is cultured to a mid-log phase in an LB culture medium (OD.sub.600 is 0.4-0.8); second, mid-log phase cells are collected and resuspended in 20 mL of an M9 culture medium (containing 5-10 g/L of glucose and 20-50 mM of NaHCO.sub.3) until OD.sub.600 is 3-5; then, 20 mL of a cell suspension is transferred into a 25 mL serum bottle and cultured for 2 hours; finally, concentrated hydrochloric acid is injected to release total inorganic carbon in the cell suspension, and the concentration of CO.sub.2 in headspace gas of the serum bottle is detected by using a gas chromatograp. RTX-QBOND (30 m; inner diameter 0.32 mm, membrane thickness 10 mm, RESTEK, Pennsylvania, the United States) is used as a gas chromatographic column. Helium is used as a carrier gas, the chromatographic column is kept at a constant temperature of 80° C., the flow rate is 15 mL/min, and the injection port pressure is 68.8 kPa.

CO.sub.2 fixation rate=(B−A) mg/mL*5 mL/(C mg*2 h)  (2) Calculation method:

[0036] Note: A and B respectively refer to the concentration of CO.sub.2 in the headspace of the serum bottle before and after culture, the headspace volume is 5 mL, the dry cell weight in the serum bottle is C mg, and the culture time is 2 hours.

Example 1: Construction of an Engineered Strain of E. coli Capable of Fixing CO.SUB.2 .to Produce Malic Acid

[0037] (1) Knockout of a Fumarate Reductase Gene frdBC in E. coli MG1655

[0038] According to an frdBC gene sequence of Escherichia coli MG1655 in an NCBI database, primers QCfrdBC-S and QCfrdBC-A were designed and knocked out (Table 1), a pKD4 plasmid was used as a template for amplifying an frdBC knockout frame, and gel recovery was performed. Note: Two FRT sites (capable of being folded under the action of a flipase to remove a DNA sequence between the FRT sites) were contained in the pKD4 plasmid, and a coding gene, namely FRT-kan-FRT, of kanamycin (kan, as a gene knockout screening pressure) was located between the two FRT sites. When a gene was knocked out, a DNA fragment of FRT-kan-FRT was amplified by the designed primers. It should be pointed out that upstream and downstream 39-49 bp of the target gene were contained in the two designed amplification primers respectively, that is to say, the DNA fragment, which was called a knockout frame of the target gene, finally obtained was “upstream 39-49 bp of the target gene-FRT-kan-FRT-upstream 39-49 bp of the target gene”. The frdBC knockout frame was transferred into competent cells containing a pKD46 plasmid of E. coli MG1655 by electrotransformation (the electrotransformation voltage and time were 1800 V and 5 ms respectively). The competent cells obtained after electrotransformation were coated on an LB solid culture medium plate containing kanamycin (50 g/mL) and subjected to inverted culture for 12-24 hours. After a single colony grew on the plate, positive transformants were screened by using verification primers YZfrdBC-S and YZfrdBC-A (Table 1).

[0039] A pCP20 plasmid was transferred into the positive transformants to remove a kanamycin resistance gene, and then the primers YZfrdBC-S and YZfrdBC-A were used for verification; the electrophoretic band size of the transformants with successful knockedout was 529 bp, and the electrophoretic band size of a control group without knockout was 1917 bp (FIG. 2). A strain obtained after successfully knocking out the frdBC gene in MG1655 was named GH0101.

[0040] (2) Knockout of a Fumarase Gene fumB in E. coli GH0101

[0041] According to an fumB gene sequence of Escherichia coli MG1655 in the NCBI database, primers QCfumB-S and QCfumB-A were designed and knocked out (Table 1), a pKD4 plasmid was used as a template for amplifying an fumB knockout frame, and gel recovery was performed. The fumB knockout frame was transferred into competent cells containing a pKD46 plasmid of E. coli GH0101 by electrotransformation (the electrotransformation voltage and time were 1800 V and 5 ms respectively). The competent cells obtained after electrotransformation were coated on an LB solid culture medium plate containing kanamycin (50 g/mL) and subjected to inverted culture for 12-24 hours. After a single colony grew on the plate, positive transformants were screened by using verification primers YZfumB-S and YZfumB-A (Table 1).

[0042] A pCP20 plasmid was transferred into the positive transformants to remove a kanamycin resistance gene, and then the primers YZfumB-S and YZfumB-A were used for verification; the electrophoretic band size of the transformants with successful knockedout was 506 bp, and the electrophoretic band size of a control group without knockout was 1940 bp (FIG. 3). A strain obtained after successfully knocking out the fumB gene in GH0101 was named GH0201.

[0043] (3) Knockout of a Lactate Dehydrogenase Gene ldhA in E. coli GH0201

[0044] According to an ldhA gene sequence of Escherichia coli MG1655 in the NCBI database, primers QCldhA-S and QCldhA-A were designed and knocked out (Table 1), a pKD4 plasmid was used as a template for amplifying an ldhA knockout frame, and gel recovery was performed. The ldhA knockout frame was transferred into competent cells containing a pKD46 plasmid of E. coli GH0201 by electrotransformation (the electrotransformation voltage and time were 1800 V and 5 ms respectively). The competent cells obtained after electrotransformation were coated on an LB solid culture medium plate containing kanamycin (50 g/mL) and subjected to inverted culture for 12-24 hours. After a single colony grew on the plate, positive transformants were screened by using verification primers YZldhA-S and YZldhA-A (Table 1).

[0045] A pCP20 plasmid was transferred into the positive transformants to remove a kanamycin resistance gene, and then the primers YZldhA-S and YZldhA-A were used for verification; the electrophoretic band size of the transformants with successful knockedout was 744 bp, and the electrophoretic band size of a control group without knockout was 2132 bp (FIG. 4). A strain obtained after successfully knocking out the ldhA gene in GH0201 was named GH0301.

[0046] (4) Knockout of an Alcohol Dehydrogenase Gene adhE in E. coli GH0301

[0047] According to an adhE gene sequence of Escherichia coli MG1655 in the NCBI database, primers QCadhE-S and QCadhE-A were designed and knocked out (Table 1), a pKD4 plasmid was used as a template for amplifying an adhE knockout frame, and gel recovery was performed. The adhE knockout frame was transferred into competent cells containing a pKD46 plasmid of E. coli GH0301 by electrotransformation (the electrotransformation voltage and time were 1800 V and 5 ms respectively). The competent cells obtained after electrotransformation were coated on an LB solid culture medium plate containing kanamycin (50 g/mL) and subjected to inverted culture for 12-24 hours. After a single colony grew on the plate, positive transformants were screened by using verification primers YZadhE-S and YZadhE-A (Table 1).

[0048] A pCP20 plasmid was transferred into the positive transformants to remove a kanamycin resistance gene, and then the primers YZadhE-S and YZadhE-A were used for verification; the electrophoretic band size of the transformants with successful knockedout was 352 bp, and the electrophoretic band size of a control group without knockout was 2676 bp (FIG. 5). A strain obtained after successfully knocking out the adhE gene in GH0301 was named GH0401.

[0049] (5) Overexpression of FDH, ACS, ACDH, FLS and DHAK Proteins

[0050] According to a formate dehydrogenase gene sequence of Clostridium ljungdahlii provided in the NCBI database, amplification primers FDH-S and FDH-A were designed (Table 1), a genome of C. ljungdahlii was used as a template for amplifying a gene sequence of an FDH protein, and after gel recovery was performed, the gene sequence of the FDH protein was ligated to a plasmid pER (BglII and XhoI) by one-step homologous recombination to obtain a recombinant plasmid pER-FDH; a gene sequence of the pER plasmid was shown in SEQ ID NO. 5. According to an acetyl CoA synthetase gene sequence of E. coli MG1655 provided in the NCBI database, amplification primers ACS-S and ACS-A (Table 1) were designed, a genome of E. coli MG1655 was used as a template for amplifying a coding gene sequence of an ACS protein, and after gel recovery was performed, the coding gene sequence of the ACS protein was ligated to a plasmid pER (BglII and XhoI) by one-step homologous recombination to obtain a recombinant plasmid pER-ACS.

[0051] According to ACDH, FLS and DHAK gene sequences provided in literatures, fragments of ACDH, FLS and DHAK encoding genes were separately obtained by gene synthesis and then ligated to a plasmid pER (BglII and XhoI) by enzyme digestion to obtain recombinant plasmids pER-ACDH, pER-FLS and pER-DHAK respectively; the five plasmids above (pER-FDH, pER-ACS, pER-ACDH, pER-FLS and pER-DHAK) were gradually assembled into a plasmid pER-CF5A by using an isocaudamer assembly technology [ACS Synth Biol 1, 256-266 (2012)]. BlnI and SpeI were used as isocaudamers, and enzyme digestion sites were shown in FIG. 6.

[0052] (6) Overexpression of ME and PTXD Proteins

[0053] According to a malic enzyme gene sequence of Clostridium acetobutylicum provided in the NCBI database, amplification primers ME-S and ME-A were designed (Table 1), a genome of Clostridium acetobutylicum was used as a template for amplifying a gene fragment encoding a malic enzyme, and the gene fragment encoding the malic enzyme was ligated to a plasmid pCDR (BglII and XhoI) by one-step homologous recombination to obtain a recombinant plasmid pCDR-ME; a gene sequence of the pCDR plasmid was shown in SEQ ID NO. 6. Fragments of PTXD encoding genes were obtained by gene synthesis and then ligated to a plasmid pCDR (BglII and XhoI) by enzyme digestion to obtain a recombinant plasmid pCDR-PTXD; the two plasmids pCDR-ME and pCDR-PTXD were assembled into a plasmid pCDR-ME-PTXD by using the isocaudamer assembly technology. BlnI and SpeI were used as isocaudamers, and enzyme digestion sites were shown in FIG. 7.

[0054] The two plasmids pER-CF5A and pCDR-ME-PTXD obtained above were transferred into competent cells of E. coli GH0401 and coated on a double-resistant plate containing spectinomycin and ampicillin, and an obtained transformant was the genetically engineered strain of E. coli in the disclosure and named GH0407. In addition, a pER empty plasmid and pCDR-ME-PTXD were transferred into competent cells of E. coli GH0401 to obtain an engineered strain GH0402 as a control strain, so as to verify the effect of a heterologous CO.sub.2 fixation pathway (HFLS, FIG. 1) on synthesis of malic acid.

Example 2 Production of Malic Acid by Fermentation of Engineered E. coli GH0402 and GH0407

[0055] A plate activation culture medium and activation culture conditions: An LB culture medium was used as the plate activation culture medium, and inverted culture in an incubator at 37° C. for 12 hours was used as an activation condition. A fermentation culture medium for fermentation contained 50 g/L of glucose, 20 mM of Na.sub.2HPO.sub.3.5H.sub.2O, 50 mM of KHCO.sub.3, 15.11 g/L of Na.sub.2HPO.sub.4.12H.sub.2O, 3 g/L of KH.sub.2PO.sub.4, 1 g/L of NH.sub.4Cl, 0.5 g/L of NaCl and 1 mL of a trace element solution; the trace element solution contained 2.4 g/L of FeCl.sub.3.6H.sub.2O, 0.3 g/L of CoCl.sub.2.6H.sub.2O, 0.15 g/L of CuCl.sub.2, 0.3 g/L of ZnCl.sub.2.4H.sub.2O, 0.3 g/L of NaMnO.sub.4, 0.075 g/L of H.sub.3BO.sub.3 and 0.495 g/L of MnCl.sub.2.4H.sub.2O, and 0.1M HCl was used as a solvent. After the engineered E. coli GH0402 and GH0407 were activated on the plate, a single colony was picked and added into a liquid LB seed culture medium and cultured at 37° C. and 200 rpm for 12 hours (OD.sub.600 is 3-4). After seed culture was completed, the single colony was inoculated into the fermentation culture medium according to an inoculation amount of 2% (v/v) and cultured for 16 hours at a temperature of 37° C. and a rotation speed of 800 rpm under an oxygen ventilation rate of 1 vvm and pH of 7.0, oxygen ventilation was closed, nitrogen was introduced for 10-20 minutes (nitrogen ventilation rate: 1 vvm) to remove residual oxygen, and the single colony was continuously fermented for 72 hours under anaerobic conditions. 250 g/L of KHCO.sub.3 was used as an acid-base neutralizer to maintain pH=7 in the whole process.

[0056] It is detected by high performance liquid chromatography (HPLC) that the final yield of malic acid in a fermentation supernatant of GH0407 is 39 g/L (FIG. 8), the yield of glucose in malic acid reaches 1.53 mol/mol (the highest reported so far) (FIG. 9), and the CO.sub.2 fixation rate of the engineered strain GH0407 is 41 mg gDCW.sup.−1 h.sup.−1 and is higher than that of most autotrophic blue-green algae (6-25 mg gDCW.sup.−1 h.sup.−1) (Table 2). HCO.sub.3.sup.− and CO.sub.2 in the fermentation solution can undergo a rapid reversible reaction, and at the same time, HCO.sub.3.sup.− can also be used as an acid-base neutralizer to control the pH of the fermentation solution; therefore, a CO.sub.2 environment can be created by adding KHCO.sub.3 into the culture medium.

[0057] Two control groups are set: (i) KHCO.sub.3 is not added into the fermentation solution, and NaOH is used as an acid-base neutralizer; (ii) the strain GH0402 without a CO.sub.2 fixation pathway (namely, without a pER-CF5A plasmid) is used as a control group. It is shown through results that when NaOH is used as the acid-base neutralizer to replace KHCO.sub.3 (that is to say, when a CO.sub.2 environment is not provided), the yield of malic acid by using the engineered strain GH0407 is only 2.3 g/L, and the yield of glucose is only 0.14 mol/mol; the final yield of malic acid in a fermentation supernatant of the control group GH0402 is 22 g/L, and the yield of glucose is 1.13 mol/mol. It can be seen from data of the control group that the production and yield of malic acid are increased by CO.sub.2.

TABLE-US-00001 TABLE 1 Sequences of gene knockout primers and protein overexpression primers Primer name Number Primer sequence QCfrdBC-S SEQ ID NO. 15 ATGGCTGAGATGAAAAACCTGAAAATTGAGGTGGTGCGCTATAACCCG GGTGTAGGCTGGAGCTGCTTC QCfrdBC-A SEQ ID NO. 16 TTACCAGTACAGGGCAACAAACAGGATTACGATGGTGGCAACCACAGT TATGGGAATTAGCCATGGTCC YZfrdBC-S SEQ ID NO. 17 TGGAGTACAGCGACGTGAAG YZfrdBC-A SEQ ID NO. 18 GGAATACGCGACCAATGAAG QCfumB-S SEQ ID NO. 19 ATGTCAAACAAACCCTTTATCTACCAGGCACCTTTCCCGATGGGGAAAG GTGTAGGCTGGAGCTGCTTC QCfumB-A SEQ ID NO. 20 TTACTTAGTGCAGTTCGCGCACTGTTTGTTGACGATTTGCTGGAAGAAG ATGGGAATTAGCCATGGTCC YZfumB-S SEQ ID NO. 21 TGTGAGCGTATCGTGCGTC YZfumB-A SEQ ID NO. 22 CGTGAAATTACAATCGCAAAC QCldhA-S SEQ ID NO. 23 ATGAAACTCGCCGTTTATAGCACAAAACAGTACGACAAGAAGTACCTGC GTGTAGGCTGGAGCTGCTTC QCldhA-A SEQ ID NO. 24 TTAAACCAGTTCGTTCGGGCAGGTTTCGCCTTTTTCCAGATTGCTTAAG ATGGGAATTAGCCATGGTCC YZldhA-S SEQ ID NO. 25 AACCCACAGCCCGAGCGT YZldhA-A SEQ ID NO. 26 GGCTTACCGTTTACGCTTTCC QCadhE-S SEQ ID NO. 27 ATGGCTGTTACTAATGTCGCTGAACTTAACGCACTCGTAGAGCGTGTAA GTGTAGGCTGGAGCTGCTTC QCadhE-A SEQ ID NO. 28 TTAAGCGGATTTTTTCGCTTTTTTCTCAGCTTTAGCCGGAGCAGCTTCTA TGGGAATTAGCCATGGTCC YZadhE-S SEQ ID NO. 29 TCATCACCGCACTGACTAT YZadhE-A SEQ ID NO. 30 TCCTTAACTGATCGGCATT FDH-S SEQ ID NO. 31 agatatacatatggcagatctGATGAAAAGTATACTAACTACTTGTCCTTATTGT FDH-A SEQ ID NO. 32 ggtttctttaccagactcgagTTAAGCGTCTTTACGCATACTCTTTT ACS-S SEQ ID NO. 33 agatatacatatggcagatctGATGAGCCAAATTCACAAACACACC ACS-A SEQ ID NO. 34 ggtttctttaccagactcgagTTACGATGGCATCGCGATAGC ME-S SEQ ID NO. 35 agatatacatatggcagatctGATGAATAATTTAAAAGGTTTAGAATTACTAAG AA ME-A SEQ ID NO. 36 ggtttctttaccagactcgagTTATCTATAGTATGGTTCCCAAATTTCA

TABLE-US-00002 TABLE 2 Comparison of CO.sub.2 fixation rate of microorganisms Strain name CO.sub.2 fixation rate Culture conditions References Botryococcus braunii  6.8 mg gDCW.sup.−1 h.sup.−1 11 L fermentation tank Bioresour Technol 101, SAG-30.81 5892-5896 (2010) Chlorella vulgaris  9.3 mg gDCW.sup.−1 h.sup.−1 Photoreactor Int J Greenh Gas Con 14, 169-176 (2013) Phaeodactylum 23.7 mg gDCW.sup.−1 h.sup.−1 Photoreactor Biotechnol Bioeng 67, tricornutum 465-475 (2000) E. coli JB 0.95 mg gDCW.sup.−1 h.sup.−1 3 L fermentation tank Bioresour Technol 150, 79-88 (2013) E. coli   41 mg gDCW.sup.−1 h.sup.−1 3.6 L fermentation The disclosure tank