Yeasts modified to use carbon dioxide

Abstract

The invention relates to yeast cells modified to express a functional type I RuBisCO enzyme, and a class II phosphoribulokinase. The expression of these enzymes recreates a Calvin cycle in said yeasts in order to enable the yeasts to use carbon dioxide.

Claims

1. A transformed yeast cell, characterized in that it contains: a) an expression cassette containing a sequence encoding the RbcL subunit of a bacterial form I RuBisCO enzyme, under the transcriptional control of a suitable promoter; b) an expression cassette containing a sequence encoding the RbcS subunit of said RuBisCO enzyme, under the transcriptional control of a suitable promoter; c) an expression cassette containing a sequence encoding the specific chaperone RbcX of said RuBisCO enzyme, under the transcriptional control of a suitable promoter; d) an expression cassette containing a sequence encoding a general bacterial chaperone GroES, under the transcriptional control of a suitable promoter; and e) an expression cassette containing a sequence encoding a general bacterial chaperone GroEL, under the transcriptional control of a suitable promoter, wherein the RbcX originates from a different bacteria than the GroES and the GroEL.

2. The transformed yeast cell according to claim 1, characterized in that the GroES and GroEL originate-from E. coli.

3. The transformed yeast cell according to claim 1, characterized in that the chaperone RbcX is a cyanobacterial chaperone.

4. The transformed yeast cell according to claim 1, characterized in that GroES and GroEL come from a bacterium that does not naturally express a RuBisCO complex.

5. The transformed yeast cell according to claim 1, characterized in that the three expression cassettes mentioned in points c), d), and e) of claim 1 form a continuous block of genetic information.

6. The transformed yeast cell according to claim 1, characterized in that the expression cassettes mentioned in points c), d), and e) of claim 1 are carried by a single episomal genetic element.

7. The transformed yeast cell according to claim 1, characterized in that said yeast is Saccharomyces cerevisiae.

8. The transformed yeast cell according to claim 1, characterized in that the bacterial form I RuBisCO enzyme is a cyanobacterial RuBisCO enzyme.

9. The transformed yeast cell according to claim 8, characterized in that said cyanobacterium belongs to the genus Synechococcus.

10. The transformed yeast cell according to claim 1, characterized in that it further contains an expression cassette containing a sequence encoding a phosphoribulokinase (PRK) under the transcriptional control of a suitable promoter.

11. The transformed yeast cell according to claim 10, characterized in that said PRK is a class II PRK.

12. The transformed yeast cell according to claim 11, characterized in that said class II PRK is selected from PRKs from Spinacia oleracea, Euglena gracilis, or Synechococcus elongatus.

13. The transformed yeast cell according to claim 10, characterized in that the promoter controlling transcription of the sequence encoding the PRK is an inducible promoter.

14. The transformed yeast cell according to claim 2, characterized in that the chaperone RbcX is a cyanobacterial chaperone.

15. The transformed yeast cell according to claim 3, characterized in that the GroES and GroEL come from a bacterium that does not naturally express a RuBisCO complex.

16. The transformed yeast cell according to claim 2, characterized in that the three expression cassettes mentioned in points c), d), and e) of claim 1 form a continuous block of genetic information.

17. The transformed yeast cell according to claim 3, characterized in that the three expression cassettes mentioned in points c), d), and e) of claim 1 form a continuous block of genetic information.

18. The transformed yeast cell according to claim 4, characterized in that the three expression cassettes mentioned in points c), d), and e) of claim 1 form a continuous block of genetic information.

19. The transformed yeast cell according to claim 2, characterized in that the expression cassettes mentioned in points c), d), and e) of claim 1 are carried by a single episomal genetic element.

20. The transformed yeast cell according to claim 2, characterized in that the chaperone RbcX is a cyanobacterial chaperone.

21. The transformed yeast cell according to claim 20, characterized in that the GroES and GroEL come from a bacterium that does not naturally express a RuBisCO complex.

22. The transformed yeast cell according to claim 20, characterized in that the three expression cassettes mentioned in points c), d), and e) of claim 1 form a continuous block of genetic information.

23. The transformed yeast cell according to claim 1, further containing: f) an expression cassette containing a sequence encoding a class II PRK under the transcriptional control of a suitable promoter, wherein the bacterial form I RuBisCO enzyme is a cyanobacterial RuBisCO enzyme and the GroES and GroEL are from E. coli.

Description

FIGURE LEGENDS

(1) FIG. 1: Analysis of total lysates of transformed strains. 1A: SDS-PAGE analysis of total lysate of strains 11.5, 11.15, 11.7, 11.17, 11.9, 11.19, 11.5, 11.19; 1B: analysis by anti-HA immunodetection of total lysate of strains 14.5, 14.12, 14.6, 14.7, 16.3, 16.5, 16.6.

(2) FIG. 2: Analysis by immunodetection of total lysate (box on the left of the Figure), and of fractions sorted by molecular weight, of strain 16.5, which co-expresses RbcL, RbcS, and RbcX, and of its control, strain 16.3, which expresses RbcX.

(3) FIG. 3: Analysis on nondenaturing gel, followed by immunodetection using an anti-RbcL antibody, of total extracts of strains 11.9, 18.3 and 22.2, and of fractions sorted by molecular weight of strain 22.2, which co-expresses RbcL, RbcS, and RbcX from S. elongatus and chaperones from E. coli. Then, in parallel, the fractions sorted by molecular weight of strains 18.3 (on the left) and 22.2 (on the right).

(4) FIG. 4: Amount of 3-phosphoglycerate detected (m/e of 185 and 186, i.e. ions of unlabeled 3-phosphoglycerate and .sup.13C-labeled 3-phosphoglycerate on a carbon in ES.sup.) obtained at various reaction times (0.10 and 60 minutes). On the left are shown the experiments carried out in the presence of .sup.13CO.sub.2 and on the right those carried out in the presence of .sup.12CO.sub.2.

(5) FIG. 5: Influence of the expression of various PRKs on cell viability, in normal atmosphere. Each strain is grown in liquid on selective CSM medium with 2 g/ml doxycycline. An equivalent of 2 OD (OD at 600 nm) is collected then washed twice to remove the doxycycline. Tenfold dilutions are prepared. 10 l of the dilutions is deposited in the form of drops (series of serial dilutions) of the cell suspensions, on agar plates (containing or not containing 2 g/ml doxycycline) and incubated at 28 C. in normal atmosphere.

(6) FIG. 6: Influence of the expression of various PRKs on cell viability, in CO.sub.2-rich atmosphere. Each strain is grown in liquid on selective CSM medium with 2 g/ml doxycycline. An equivalent of 2 OD (OD at 600 nm) is collected then washed twice to remove the doxycycline. Tenfold dilutions are prepared. 10 l of the dilutions is deposited in the form of drops (series of serial dilutions) of the cell suspensions, on agar plates (containing or not containing 2 g/ml doxycycline) and incubated at 28 C. in closed bags the atmosphere of which contains at least 90:10 (v/v) carbon dioxide/air.

(7) FIG. 7: Maximum growth rate (.sub.max) ratios for each strain. Dark bars: induced state (high level of expression) of the tetO promoter (medium not containing doxycycline); light bars: (partially) repressed state (low level of expression) of the tetO promoter (medium containing 2 g/ml doxycycline).

(8) FIG. 8: Detection of ribulose-1,5-diphosphate (molar mass 309 g/mol) as a function of elution time in various extracts. The panel on the left shows the chromatograms of strain W303-1B grown in closed tubes containing selective CSM medium; the panel at center shows the chromatograms of strain CENPK grown in closed tubes and selective CSM medium, the panel on the right represents the chromatograms obtained for strain CENPK grown in closed tubes and minimum medium.

(9) FIG. 9: Evaluation of enzyme activity of synthetic RuBisCO complex on strains CEN.PK no. 3 and 4. PRK: phosphoribulokinase; RbcSLX: products of RbcL, RbcS and RBCX genes; GroESL: products of GroEL and GroEL genes from E. coli.

(10) FIG. 10: RuBisCO activity of an extract of yeast CEN-PK no. 3 containing the complete engineering, in the presence and the absence of bovine carbonic anhydrase.

(11) FIG. 11: Change in ethanol and biomass concentration during anaerobic cultures (Rub: RbcS+RbcL; Prk: phosphoribulokinase; Chaperones: RbcX+(GroES+GroEL) E. coli). .square-solid. strain CEN.PK no. 13b and strain CEN.PK no. 3.

(12) FIG. 12: Change in concentrations of biomass, formate and glucose during aerobic cultures (Rub: RbcS+RbcL; Prk: phosphoribulokinase; Chaperones: RbcX+(GroES+GroEL) E. coli). Biomass generation (g/l, left-hand ordinate): .square-solid. strain CEN.PK no. 2 (RbcL, RbcS, RbcX, GroES_coli, GroEL_coli), strain CEN.PK no. 3 (PRK, RbcL, RbcS, RbcX, GroES_coli, GroEL_coli); Glucose consumption (g/l, left-hand ordinate): .circle-solid. strain CEN.PK no. 2, strain CEN.PK no. 3; Formate consumption (g/l, right-hand ordinate): .box-tangle-solidup. strain CEN.PK no. 2, strain CEN.PK no. 3.

(13) FIG. 13: Extracts of metabolomic analysis carried out strains comprising the complete engineering (CEN.PK no. 3 (PRK, RbcL, RbcS, RbcX, GroES_coli, GroEL coli)) or without PRK (CEN.PK no. 2 (RbcL, RbcS, RbcX, GroES_coli, GroEL_coli)). The analysis shows in particular a strong accumulation of Fructose-6P (F6P), Fructose-1,6diP (FBP), Glucose-6P (G6P), Sedoheptulose-7P (S7P), Xylolose-5P (Xylu5P), Ribulose-5P (Ribu5P), Ribose-5P (Rib5P), Ribulose-1,5diP (RibuDP) and Glycerate-3P (Gly3P).

(14) FIG. 14: Metabolic simulation for a modified yeast cell according to the invention.

EXAMPLE 1: Expression and Assembly of the Synechococcus elongatus Rubisco Complex in the Yeast Saccharomyces cerevisiae

(15) Synthetic genes encoding the RbcS and RbcL subunits and the specific chaperone RbcX of the RuBisCO from Synechococcus elongates pCC6301, and optimized for expression in yeast, were prepared and cloned into the plasmid pBSII (Genecust). Variants in which an HA tag was added at the 3 end of the coding sequence were also constructed.

(16) The sequences of these synthetic genes (with no HA tag) are indicated in the appended sequence list under numbers SEQ ID NO: 1 (RbcL), SEQ ID NO: 2 (RbcS) and SEQ ID NO: 3 (RbcX).

(17) The sequences encoding the E. coli chaperones GroES and GroEL were amplified from E. coli cultures and cloned into the plasmid pSC-B-amp/kan (Stratagene).

(18) The sequences collected from the cloning vectors were introduced into yeast expression vectors. These host vectors are listed in Table I below.

(19) TABLE-US-00001 TABLE I Yeast origin Selection Transcription cassette E. coli Names of replication marker (promoter-terminator) replicon pFPP5 2u URA3 pGAL10-CYC1-tPGK Yes (AmpR) pFPP10 2u URA3 pTDH3- -tADH Yes (AmpR) pFPP11 2u URA3 pTDH3- -tCYC1 Yes (AmpR) pFPP12 2u URA3 pTGI1- -tCYC1 Yes (AmpR) pFPP13 ARS-CEN6 LEU2 pTEF1-tPGK Yes (AmpR) Note: pGAL10-CYC1: synthetic promoter composed of the UAS of the GAL10 gene and the transcription initiation of the CYC1 gene (Pompom et al., Methods Enzymol, 272, 51-64, 1996).

(20) The expression cassettes thus obtained are listed in Table II below.

(21) TABLE-US-00002 TABLE II Names Promoter Open reading frame Tag Terminator CAS1 TEF1p RbcL- HA PGK CAS2 TEF1p RbcS- HA PGK CAS3 TEF1p RbcX- HA PGK CAS4 PGI1p RbcX None CYC1 CAS5 TDH3p RbcL- HA ADH1 CAS6 TDH3p RbcL None ADH1 CAS16 TEF1 RbcS None PGK CAS17 TDH3 RbcL- HA PGK CAS18 TDH3 RbcL None ADH CAS19 TEF1p RbcX None PGK CAS20 PGI1 RbcX- HA CYC1 CAS21 PGI1p GroES None CYC1 CAS22 TDH3 GroEL None ADH

(22) In certain vectors, two or three cassettes were inserted. To that end, the plasmids were amplified in the bacterium Escherichia coli DH5 and prepared by maxiprep, then digested by suitable restriction enzymes. Lastly, the fragments are integrated into host vectors by ligation by T4 ligase (Fermentas). The list of vectors constructed is indicated in Table III below.

(23) TABLE-US-00003 TABLE III Names Origin type Cassette 1 Cassette 2 Cassette 3 Markers Host vector pFPP6 2u CAS1 None None URA3 pFPP5 pFPP7 2u CAS2 None None URA3 pFPP5 pFPP18 2u CAS2* CAS6 None URA3 pFPP5/pFPP10 pFPP19 2u CAS2 CAS6 None URA3 pFPP5/pFPP10 pFPP23 ARS416-CEN6 CAS3 None None LEU2 pFPP13 pFPP40 2u CAS5 None None URA3 pFPP10 pFPP45 2u CAS6 CAS16 None URA3 pFPP5/pFPP10 pFPP48 2u CAS20 None None URA3 pFPP12 pFPP49 2u CAS19 None None LEU2 pFPP12/pFPP13 pFPP55 ARS415-CEN6 CAS19 CAS21 CAS22 LEU2 pFPP13 pFPP56 ARS415-CEN6 CAS19 CAS21 CAS22* LEU2 pFPP13 *reverse orientation

(24) Various vectors or combinations of vectors were used to transform cells of the yeast S. cerevisiae (strain W303.1B).

(25) These vectors and combinations of vectors are indicated in Table IV below.

(26) TABLE-US-00004 TABLE IV Proteins expressed ( indicates C-terminal Transformed Parental fusion with an HA tag) strain strain Vector 1 Vector 2 Vector 3 RbcS RbcL RbcX GroES GroEL PRK 11.19 W303 pCM185 pFPP23 pFPP19 X X X 18.3 W303 pFPP45 pFPP49 X X X 22.2 W303 pFPP45 pFPP56 X X X X X 22.3 W303 pFPP45 pFPP55 X X X X X 30.1 W303 pCM185 11.5 W303 pCM185 pFL36 pFPP5 11.7 W303 pCM185 pFL36 pFPP18 X X 11.9 W303 pCM185 pFL36 pFPP19 X X 11.15 W303 pCM185 pFPP23 pFPP5 X 11.17 W303 pCM185 pFPP23 pFPP18 X X X 14.5 W303 pFPP6 X 14.12 W303 pFPP40 X 14.6 W303 pFPP7 X 14.7 W303 pFPP23 X 16.3 W303 pFPP48 X 16.5 W303 pFPP43 pFPP23 X X X 16.6 W303 pFPP43 X X yFB3 CEN.PK pFPP45 pFPP20 pFPP56 X X X X X X Notes: pCM185: plasmid ATCC 87659; pFL36: plasmid ATCC 77202

(27) The transformed cells are grown at 30 C. in ambient air on YNB medium (yeast without nitrogen base supplemented with 6.7 g/l ammonium sulfate, 20 g/l glucose, 20 g/l agar for the agars) supplemented with commercial CSM medium (MP Biomedicals) suited to the selection markers of the plasmids used for the transformation. The cultures are stopped by cooling at 4 C. a generation before the end of the exponential phase.

(28) An aliquot is taken from each culture and the cells are lysed with soda in the presence of SDS for analysis of total proteins on denaturing SDS gel.

(29) The remainder of the cultures is centrifuged, then spheroplasts are prepared by enzymatic digestion of cell walls with a zymolyase-cytohelicase mixture in hypertonic sorbitol medium (1.2 M sorbitol). The spheroplasts are washed in hypertonic sorbitol medium in the presence of saturating concentrations of PMSF and EDTA (protease inhibitors), then broken by repeated pipetting and mild sonication in isotonic sorbitol medium (0.6 M). After centrifugation at low speed (1500 rpm) to remove large debris then at moderate speed (4000 rpm) to collect debris of intermediate sizes and mitochondria, the supernatant is collected and the proteins are precipitated at 80% saturation of ammonium sulfate with pH maintained at 6.5-7.0. The precipitate is redissolved and dialyzed in the presence of protease inhibitors, then fractionated by molecular sieving on a Sephacryl S300 column (GE Healthcare). The eluted fractions are combined in pools for gel analysis.

(30) Total lysate and fractions sorted by molecular weights (native globular protein range of 10.sup.4 to 1.510.sup.6 daltons) are analyzed on denaturing SDS-PAGE gel and nondenaturing gel (prestaining with Coomassie blue-PAGE). The gel is stained with Coomassie blue and the blot with Ponceau red for analysis of total proteins. RbcL, RbcS and RbcX proteins are detected after electrotransfer onto charged nylon by immunodetection. In the case of RbcL, detection can be carried out directly using an anti-RbcL antibody, and in the case of RbcS and RbcX, indirectly via an anti-HA-tag antibody. The various experiments were repeated while alternating co-expression of tag proteins or not in order to verify that the presence of the tags did not affect folding or assembly of the complexes.

(31) FIG. 1 represents the analysis of total lysates of transformed strains.

(32) The two subunits are expressed in yeast. RbcL is expressed at high level (visible by nonspecific staining of total proteins of an extract). The level of RbcS expression has not been quantified but appears similar to that of RbcL on the basis of anti-HA immunodetection. The two proteins exhibit no sign of degradation (absence of blurred or multiple bands) suggesting good folding quality and resistance to endogenous proteases. The chaperone RbcX is expressed as well and exhibits no sign of degradation. The plasmid systems for co-expressing the three components are operational and do not show notable interference with expression of the various components.

(33) FIG. 2 represents the analysis by immunodetection of total lysate (box on the left of the Figure), and fractions sorted by molecular weight of strain 16.5, which co-expresses RbcL, RbcS, and RbcX, and its control, strain 16.3, which expresses RbcX.

(34) Monomodal distribution of the RbcL subunit is observed within complexes 500 kDa or larger in size whereas the mass of the isolated subunit is 55 kDa. Distribution of RbcS and RbcX is on the contrary bimodal, one mode being of size similar to that observed for RbcL, the other corresponding to small sizes, close to those of isolated RbcS and RbcX proteins. Native RuBisCO complex is not convincingly visible with native gel and with nonspecific staining at the expected size (about 500 kDa) under these conditions. Nevertheless, a very large complex is detectable at about 750-1000 kDa (larger than the expected size) by immunodetection of RbcL.

(35) FIG. 3 represents the results of the analysis on nondenaturing gel, followed by immunodetection using an anti-RbcL antibody, of total extracts of strains 11.9, 18.3 and 22.2, and fractions sorted by molecular weight of strain 22.2, which co-expresses RbcL, RbcS, and RbcX from S. elongatus and chaperones from E. coli. Then, in parallel, fractions sorted by molecular weight of strains 18.3 (on the left) and 22.2 (on the right).

(36) These results show that co-expression with the chaperones GroES and GroEL induces a reduction in the size of the high molecular weight complex (about 750-1000 kDa) that was detected in the absence of these chaperones; in cells co-expressing RbcL, RbcS, RbcX, GroES and GroEL, a well-defined band corresponding to the expected size (about 500 kDa) for native RuBisCO complex is observed.

(37) These results show that a prokaryotic form I RuBisCO complex can be expressed and correctly assembled in S. cerevisiae cells, this assembly being improved by the presence of the general chaperones GroES and GroEL.

(38) For the analysis of RuBisCO activity in vitro, the extraction of soluble proteins of strain yFB3 is carried out. The cells are grown at 30 C. in ambient air on YNB (yeast without nitrogen base) medium, supplemented with 6.7 g/l ammonium sulfate, 20 g/l glucose, 20 g/l agar for the agars) with commercial CSM medium (MP Biomedicals), and suited to the selection markers of the plasmids used (medium without leucine, uracil and tryptophan for yFB3). The cultures are stopped by cooling at 4 C. a generation before the end of the exponential phase. The cultures are centrifuged, then spheroplasts are prepared by enzymatic digestion of cell walls with a zymolyase-cytohelicase mixture in hypertonic sorbitol medium (1.2 M sorbitol). The spheroplasts are washed in hypertonic sorbitol medium in the presence of 1 mM PMSF and EDTA (protease inhibitors), then broken by repeated pipetting and mild sonication in isotonic sorbitol medium (0.6 M). After centrifugation at low speed (200 g for 5 min) to remove large debris then at moderate speed (1500 g for 10 min) to collect debris of intermediate sizes and mitochondria, the supernatant is collected.

(39) The tests for activity on the protein extracts are carried out in 50 mM TRIS/HCl (pH 7.5), 60 mM NaHCO.sub.3 (.sup.13C or .sup.12C) 10 mM MgCl.sub.2 in the presence of 2 mM ribulose diphosphate (RiDP) and 0.5 mg/ml total proteins of yFB3 extracts. At t=10 min and t=60 min, 100 l of reaction mixture is taken, the reaction is stopped by adding 2 l of HCl, and the sample is centrifuged for 10 min at 9300 g then analyzed by HPLC/MS (ion-pairing reversed-phase C18 with 10 mM tributylamine acetate/acetonitrile pH 6.0 gradient). Metabolites are detected by negative-ion electrospray mass spectrometry, and identified on the basis of their m/e ratios and elution times, compared with those of standard compounds.

(40) The results are illustrated by FIG. 4.

(41) In the presence of .sup.13CO.sub.2, the labeling ratio of 3-phosphoglycerate formed at 60 min is 52% as expected. Indeed, as represented at the bottom of FIG. 4, the reaction catalyzed by RuBisCO is the formation of two 3-phosphoglycerate molecules from one CO.sub.2 molecule and one RiDP molecule. In the presence of .sup.12CO.sub.2, 3-phosphoglycerate is formed but only in its unlabeled form.

(42) The RuBisCO present in the extracts is thus able to incorporate the carbon of CO.sub.2 to produce 3-phosphoglycerate.

EXAMPLE 2: Phosphoribulokinase Expression in the Yeast Saccharomyces cerevisiae

(43) Synthetic genes encoding five PRKs of different origin: Synechococcus elongatus (Syn), Rhodobacter sphaeroides (Rsph), Rhodopseudomonas palustris (Rpal), Spinacia oleracea (Sole), Euglena gracilis (Egra) and optimized for expression in yeast, and flanked or not flanked with a C-terminal HA tag, were prepared. The sequences of these synthetic genes (with no HA tag) are indicated in the appended sequence list under numbers SEQ ID NO: 4 to SEQ ID NO: 8, respectively.

(44) Rsph and Rpal PRKs are class I PRKs existing in native form as an octamer for Rsph and as a hexamer for Rpal. Sole, Egra and Syn kinases are class II kinases whose native form is a dimer for the first two and a tetramer for the third.

(45) The Rhodobacter sphaeroides (Rsph), Rhodopseudomonas palustris (Rpal), Euglena gracilis (Egra) and Spinacia oleracea (Sole) sequences were synthesized by the company Genecust and delivered in a pBlueScript II+ plasmid. The plasmids were amplified in the bacterium Escherichia coli DH5. A maxiprep extraction is carried out for each plasmid. They are then digested with the enzymes BamHI and PstI then the digestion product is deposited on a 0.8% agarose gel containing SYBER Safe. Migration is carried out in 1TAE buffer at 50 V for 30 minutes. Bands corresponding to open reading frames (972 bp for PRK from Rpal, 966 bp for Rsph, 1461 bp for Egra and 1277 bp for Sole) are cut out of the gel and DNA is extracted with the gel extraction kit from the company Fermentas. Lastly, the fragments are integrated into the vectors pCM185, pCM188-2 and pCM188-7 by ligation by ligase T4 (FERMENTAS) under the control of the doxycycline-repressible tetO promoter, to give the expression vectors pFPP20, pJLP1, pJLP2, pJLP3, pJLP4, respectively.

(46) The cassettes and expression vectors thus obtained are listed in Table V below.

(47) TABLE-US-00005 TABLE V Names Origin type Promoter Terminator Open reading frame Markers Host vector pCM185 ARS416-CEN4 TetO7 CYC1 TRP1 pCM188-2 ARS416-CEN4 TetO7 CYC1 URA3 pCM188-7 ARS416-CEN4 TetO7 CYC1 URA3 pFPP20 ARS416-CEN4 TetO7 CYC1 PRK S. elongatus TRP1 pCM185 pFPP21 ARS416-CEN4 TetO2 CYC1 PRK S. elongatus URA3 pCM188-2 pFPP22 ARS416-CEN4 TetO7 CYC1 PRK S. elongatus URA3 pCM188-7 pJLP1 ARS416-CEN4 TetO7 CYC1 PRK E. gracilis HA tag TRP1 pCM185 pJLP2 ARS416-CEN4 TetO7 CYC1 PRK R. sphaeroides HA tag TRP1 pCM185 pJLP3 ARS416-CEN4 TetO7 CYC1 PRK R. palustris HA tag TRP1 pCM185 pJLP4 ARS416-CEN4 TetO7 CYC1 PRK S. oleracea HA tag TRP1 pCM185

(48) These vectors were used to transform cells of S. cerevisiae strains W303.1B and CNPK. The first of these strains is a typical laboratory strain, the second is a semi-industrial strain.

(49) The transformation was carried out according to the protocol of Chen et al. (Curr Genet. 1992, 21, 83-4), while maintaining at each transformation and subcloning step a doxycycline concentration of 2 g/ml, suited to repression of the tetO promoter. The transformants were stored in glycerol-containing medium (50% glycerol) at 80 C. in the presence of 2 g/ml doxycycline.

(50) The transformed strains obtained are listed in Table VI below.

(51) TABLE-US-00006 TABLE VI Transformed Parental PRK strain strain Vector 1 Vector 2 Vector 3 expressed 11.5 W303 pCM185 pFL36 pFPP5 30.2 W303 pFPP20 PRKsyn 11.6 W303 pFPP20 pFL36 pFPP5 PRKsyn yJL1 W303 pJLP1 PRK Egra yJL2 W303 pJLP2 PRK Rsph yJL3 W303 pJLP3 PRK Rpal yJL4 W303 pJLP4 PRK Sole yJL5 CENPK pFPP20 PRKsyn yJL6 CENPK pJLP1 PRK Egra yJL7 CENPK pJLP2 PRK Rsph yJL8 CENPK pJLP3 PRK Rpal yJL9 CENPK pJLP4 PRK Sole

(52) The transformed cells are put in preculture from the stock in YNB medium (yeast without nitrogen base supplemented with 6.7 g/l ammonium sulfate, 20 g/l glucose, 20 g/l agar for the agars) with commercial CSM medium (MP Biomedicals) suited to the support of plasmid selection and containing a concentration of 2 g/ml doxycycline suited to the repression of PRK expression.

(53) The influence of the expression of the various PRKs on cell viability was evaluated on agar medium in the presence or absence of doxycycline: Each strain is grown in liquid on selective CSM medium with 2 g/ml doxycycline. An equivalent of 2 OD (OD at 600 nm) is collected then washed twice to remove the doxycycline. Tenfold dilutions are prepared. 10 l of the dilutions is deposited in the form of drops (series of serial dilutions) of the cell suspensions, on agar plates (containing or not containing 2 g/ml doxycycline) and incubated at 28 C. in normal atmosphere or alternatively in closed bags the atmosphere of which contains at least 90:10 (v/v) carbon dioxide/air.

(54) The results in normal atmosphere are illustrated by FIG. 5. The results in CO.sub.2-rich atmosphere are illustrated by FIG. 6.

(55) It is noted that all the PRKs are more or less toxic in strain W3031B with high level of expression (induced). Nevertheless, toxicity appears much lower in strain CENPK, where only the Syn PRK is toxic in the induced state.

(56) Other experiments show that in strain W303.1B, toxicity is strongly attenuated in an atmosphere poor in oxygen and rich in carbon dioxide.

(57) The influence of the expression of the various PRKs on cell growth was evaluated on cultures in liquid medium: The strains are grown in selective CSM medium in closed tubes (containing or not containing 2 g/ml doxycycline). Growth is monitored by measuring optical density at 600 nm until entry into stationary phase. For each strain, the relationship between the maximum growth rate (population increase per unit time) of the strain and that of the control strain (strain+empty plasmid) is determined.

(58) The maximum growth rate (.sub.max) ratios for each strain are illustrated by FIG. 7.

(59) These results confirm that the toxicity of kinases in the context of strain CNPK 113-7D is lower than that of strain W303.1B.

(60) A dose (induction level)-response (growth rate) toxicity effect is observed only for Sole kinase and in W303.1B.

(61) In W303.1B, a significant toxicity of Rpal, Rsph, Syn kinases weakly and strongly expressed is observed. Toxicity appears lower for Egra kinase.

(62) For the analysis of the metabolite ribulose-1,5 bisphosphate of the central carbon ring, the cells are washed to remove the doxycycline and placed in liquid culture at 30 C. on YNB (yeast without nitrogen base) medium supplemented with 6.7 g/l ammonium sulfate, 20 g/l glucose, (20 g/l agar for the agars) supplemented with commercial CSM medium (MP Biomedicals) suited to the selection marker of the plasmid used. The cultures are prepared in closed tubes with no oxygen supply beyond 3-10 volumes of air (not replenished) per volume of culture medium. Carbon dioxide stemming from the culture is thus maintained within the volume of the culture tube. This procedure limits the toxicity of the expression.

(63) Metabolism is blocked by diluting the culture in 60:40 (v/v) methanol-water at 80 C. (mixture maintained at 40 C. in a dry ice/acetonitrile bath), followed by rapid centrifugation (temperature maintained below 20 C.) and cell lysis in a methanol-water (60:40 v/v) mixture containing 0.3 M soda then freezing at 80 C. according to the protocol described by Luo et al., (J. Chromatography A 1147:153-164, 2007).

(64) After thawing, an aliquot is neutralized with glacial acetic acid, centrifuged, and the supernatant analyzed by HPLC/MS (ion-pairing reversed-phase C18 with tributylamine acetate/acetonitrile pH 6.0 gradient). Metabolites are detected by negative-ion electrospray mass spectrometry and identified on the basis of their m/e mass ratios and elution times, compared with those of standard compounds.

(65) The results are illustrated by FIG. 8.

(66) The activity level (not normalized to level of expression) estimated by the level of accumulation of ribulose-1,5-diphosphate produced from the reaction appears: very high for Syn PRK even in repressed condition (50% of induced level). This activity is accompanied by toxicity with a significant drop in the level of intracellular ATP; detectable but weaker for Egra and Sole PRKs in minimum medium; undetectable under the conditions used for RspH and Rpai PRKs; dependent on the culture medium, with for Syn PRK a level of ribulose-1,5-diphosphate accumulation much higher in poor medium than rich.

(67) The whole of these observations indicates that only class II kinases lead to the accumulation of high levels of ribulose diphosphate in S. cerevisiae.

EXAMPLE 3: Phenotypic Characterization of Strains Containing the Carboyeast Engineering In Vitro by Study of the Functionality of Rubisco Complex Expressed in Yeast and Parameters Controlling Same

(68) As described in FIG. 4, the functionality of the artificial RuBisCO complex was shown in vitro by tests for RuBisCO activity on a synthetic substrate (ribulose diphosphate) from yeast extracts containing the complete or partial engineering, and by evaluating the appearance of the product of the reaction it catalyzes, namely 3-glycerophosphate.

(69) 3.1. Constructions and Strains Used

(70) The present example was carried out using the constructions and transformed strains described in Tables VII to IX below.

(71) TABLE-US-00007 TABLE VII Expression cassettes Termi- Names Promoter Open reading frame Tag nator CAS6 TDH3p RbcL S. elongatus optimized None ADH1t CAS7 TetO7p PRK S. elongates optimized None CYC1t CAS16 TEF1p RbcS S. elongates optimized None PGKt CAS19 TEF1p RbcX S. elongates optimized None PGKt CAS21 PGI1p GroES E. coli None CYC1t CAS22 TDH3p GroEL E. coli None ADH1t CAS23 PGI1p GroES S. elongates optimized None CYC1t CAS25 TDH3p GroEL2 S. elongates optimized None ADH1t CAS28 PGI1p polylinker None CYC1t CAS33 TEF1p polylinker None PGKt

(72) TABLE-US-00008 TABLE VIII Expression vectors (references to Table VII for the cassettes) Auxotrophy Host E. coli Names Origin type Cassette 1 Cassette 2 Cassette 3 markers vector replicon pFPP13 ARS415- CAS33 None None LEU2 pFL36 Yes CEN6 (AmpR) pFFP53 ARS415- CAS19 CAS28 None LEU2 pFL36 Yes CEN6 (AmpR) pFFP56 ARS415- CAS19 CAS21 CAS22* LEU2 pFL36 Yes CEN6 (AmpR) pFB05 ARS415- CAS19 CAS25* CAS21 LEU2 pFFP56 Yes CEN6 (AmpR) pFB07 ARS415- CAS23 CAS22* CAS19 LEU2 pFFP56 Yes CEN6 (AmpR) pFB08 ARS415- CAS23 CAS25* CAS19 LEU2 pFFP56 Yes CEN6 (AmpR) pFB09 ARS415- CAS21 CAS22* None LEU2 pFFP56 Yes CEN6 (AmpR) pFPP45 2 CAS6 CAS16 None URA3 PYeDP51 Yes (AmpR) pFPP20 ARS416- CAS7 None None TRP pCM185 Yes CEN4 (AmpR) *reverse orientation

(73) TABLE-US-00009 TABLE IX Combination of plasmids and strains (references to Table VIII.) Combination Parental Proteins expressed no. strain Vector 1 Vector 2 Vector 3 RbcS RbcL RbcX PRKsyn GroES GroEL 1b CEN.PK pYeDP51 pCM185 pFPP13 1605 2 CEN.PK pFPP45 pCM185 pFPP56 X X X coli coli 1605 3 CEN.PK pFPP45 pFPP20 pFPP56 X X X syn coli coli 1605 4 CEN.PK pFPP45 pFPP20 pFPP53 X X X syn 1605 5 CEN.PK pFPP45 pCM185 pFPP53 X X X 1605 13b CEN.PK PYeDP51 pCM185 pFPP56 X coli coli 1605 15 CEN.PK PYeDP51 pFPP20 pFPP56 X syn coli coli 1605 17b CEN.PK pFPP45 pFPP20 pFPP13 X X syn 1605 101 CEN.PK pFPP45 pFPP20 pFB08 X X X Syn syn L2 1605 syn (Syn: S. elongatus; coli: E coli; L2 syn: GroEL2 S. elongatus)

(74) Notes: 1. pCM185: Commercial plasmid (ATCC 87659) 2. pFL36: Commercial plasmid (ATCC 77202) 3. PYeDP51: Empty plasmid, described in the following article: Urban P, Mignotte C, Kazmaier M, Delorme F, Pompom D. Cloning, yeast expression, and characterization of the coupling of two distantly related Arabidopsis thaliana NADPH-cytochrome P450 reductases with P450 CYP73A5. J Biol Chem. 1997 Aug. 1; 272(31):19176-86. 4. The other abbreviations refer to S. cerevisiae genes described in the data banks. 5. Synthetic genes: The Synechococcus elongatus genes encoding the chaperone specific to RuBisCO assembly (RbcX), as well as the general chaperones GroES, GroEL1 and GroEL2, were resynthesized after re-encoding for yeast implementing a proprietary inhomogeneous codon bias and cloned into pCC6301 (commercial). 6. E. coli chaperones GroES and GroEL were amplified from the bacterium, cloned into pSC-B-amp/kan (Stratagene) and assembled without re-encoding in the expression vectors (see Example 1). 7. The Synechococcus elongatus RbcS, RbcL, RbcX and PRK sequences were described in Examples 1 and 2. 8. The re-encoded sequences of cDNAs encoding Synechococcus elongatus chaperonins are described in the sequence listing (SEQ ID NO: 9 to 11) and inserted by homologous recombination in previously linearized vector pUC57 by co-transforming the two molecules in yeast. Similarly, the ORFs were amplified by PCR from previous constructions, generating flanking regions homologous to the promoters and terminators carried by vector pFPP56. That allowed cloning by homologous recombination by co-transforming this PCR product in a yeast strain with previously linearized vector pFPP56, generating the various expression vectors described in Table VIII according to the cassettes described in Table VII.
3.2. Evaluation of the Enzyme Activity of Synthetic RuBisCO Complex

(75) For the extraction of soluble proteins of strains CEN.PK no. 3 and CEN-PK no. 4, the cells are grown at 30 C. in ambient air with shaking on YNB (yeast without nitrogen base) medium, supplemented with 6.7 g/l ammonium sulfate, 20 g/l glucose, 20 g/l agar for the agars, with commercial CSM medium (MP Biomedicals), suited to the selection markers of the plasmids used (medium without leucine, uracil and tryptophan). The cultures are stopped by cooling at 4 C. a generation before the end of the exponential phase. The cultures are centrifuged, then spheroplasts are prepared by enzymatic digestion of cell walls with a zymolyase-cytohelicase mixture in hypertonic sorbitol medium (1.2 M sorbitol). The spheroplasts are washed in hypertonic sorbitol medium in the presence of 1 mM PMSF and EDTA (protease inhibitors), then broken by repeated pipetting and mild sonication in isotonic medium (0.6 M sorbitol). After centrifugation at low speed (200 g for 5 min) to remove large debris then at moderate speed (1500 g for 10 min) to collect debris of intermediate sizes and mitochondria, the supernatant is collected.

(76) The tests for activity on the protein extracts are carried out in 50 mM TRIS/HCl (pH 7.5), 60 mM NaHCO.sub.2, 10 mM MgCl.sub.2 in the presence of 2 mM ribulose diphosphate (RiDP) and 0.05 mg/ml total proteins of the extracts. At various times, 60 l of reaction mixture is taken, the reaction is stopped by adding 2 l of HCl (12.1 M), and the sample is centrifuged for min at 9300 g then analyzed by HPLC/MS (ion-pairing reversed-phase C18 with 10 mM tributylamine acetate/acetonitrile pH 6.0 gradient). Metabolites are detected by negative-ion electrospray mass spectrometry and identified on the basis of their m/e ratios and elution times, compared with those of standard compounds.

(77) The results are illustrated by FIG. 9. This Figure represents on the ordinate the number of moles of 3-phosphoglycerate detected (m/e of 185) obtained at various reaction times on the abscissa.

(78) It is noted that for a complete engineering (CEN.PK no. 3: RbcS+RbcL+PRK+chaperones RbcX and GroES and GroEL from E. coli), referred to as the CARBOYEAST engineering, and a non-limiting substrate, the amount of product resulting from catalytic activity of the synthetic RuBisCO enzyme increases linearly in time. The RuBisCO complex expressed in yeast by the engineering is thus functional and stable.

(79) It appears clearly that the association of the pair of general bacterial chaperones GroES GroEL with the chaperone RbcX, specialized in RuBisCO complex folding, is essential (FIG. 9 and Table X).

(80) However, under the test conditions illustrated, co-expression of a combination of general bacterial chaperones (GroES and GroEL) from E. coli, associated with the specific chaperone RbcX from S. elongatus, is more effective for reconstructing functionality of the RuBisCO complex, itself from S. elongatus, than the same association but wherein all the elements come from the same organism, S. elongatus (Table X, lines 1 and 3).

(81) TABLE-US-00010 TABLE X Tests for RuBisCO activity in vitro carried out according to a protocol similar to that described before from extracts of CEN-PK strains grown on glucose and containing the engineering indicated in the first column. The tests are carried out during 80 min of incubation with 0.01-0.02 mg of protein of soluble extract of yeast in a reaction volume of 200 l containing 2 mM ribulose diphosphate at room temperature. The activities are given in nmol of 3-phosphoglycerate formed/min/mg total proteins in the extract. Strains A B C CEN.PK no. 3 RbcS/RbcL/RbcX/PRK/(GroES/ 20 13 20 GroEL) E. coli CEN.PK no. 2 RbcS/RbcL/RbcX/(GroES/ ND 5 2.5 GroEL) E. coli CEN.PK no. 101 RbcS/RbcL/RbcX/PRK/(GroES/ ND ND 1.5 GroEL2) S. elongatus
3.3. Synthetic RuBisCO Incorporates .sup.13C-Labeled CO.sub.2 to Integrate Same in the Reaction Product

(82) The isotope incorporation experiment described above (FIG. 4) illustrates by quantification of labeled 3-glycerophosphate the capacity of the RuBisCO complex to produce labeled 3-glycerophosphate from ribulose diphosphate, by fixing carbon from .sup.13C-labelled bicarbonate molecules.

(83) 3.4. RuBisCO Activity is Increased by the Presence of Carbonic Anhydrase

(84) Carbonic anhydrase, by catalyzing the interconversion of bicarbonate to solvated carbon dioxide, is a known cofactor of the reaction. This example confirms the expected behavior for such a reaction. Interestingly, tests for activity in vitro show that adding bovine carbonic anhydrase in a final concentration of 10 g/ml in the reaction volume of a test for RuBisCO activity, described above, increases the potential of the RuBisCO complex by a factor of three to four (FIG. 10). That suggests that optimization of the CO.sub.2 concentration around the complex significantly increases the activities observed in the preceding test, which thus represents a minimal value for the reconstituted activities. Other factors could also contribute thereto in vivo; the measured values are thus only minimum values.

EXAMPLE 4: Phenotypic Characterization of Strains Containing the Engineering

(85) 4.1. Anaerobic Culture Shows an Increase in Ethanol Production

(86) Precultures were prepared on chemically defined medium. After thawing, 1 ml of a stock tube (80 C.) was taken to inoculate a penicillin bottle (100 ml) containing 10 ml of culture medium (including 0.1 g/l formic acid supplemented with 20 g/l glucose), incubated for 18 hours at 30 C. and 120 rpm. The precultures were prepared in anaerobiosis (bottles previously flushed with nitrogen) and in the presence of doxycycline (2/ml) in order to avoid the toxicity problems observed in the presence of the PRK gene.
The precultures were then washed three times (centrifugation, resuspension, vortex for 15 s) with physiological saline (NaCl, 9 g/l), then the cell pellet was resuspended in culture medium without doxycycline.
These cells stemming from the precultures were then inoculated in order to reach an initial optical density of 0.05 (or 0.1 g/l). The starting culture volume was 50 ml in aerobiosis (250 ml baffled Erlenmeyer flasks) or 35 ml in anaerobiosis (100 ml penicillin bottles).
The cultures were stopped after all glucose was consumed or ethanol production stopped.

(87) Anaerobic culture made it possible to characterize phenotypically strains containing the complete CARBOYEAST engineering or isolated elements, so as to characterize the influence of each on yeast.

(88) FIG. 11 and Table XI show that, during anaerobic cultures on glucose, the complete CARBOYEAST engineering (RuBisCO_PRK Chaperones) or (RbcS+RbcL+PRK+RbcX+(GroES+GroEL) E. coli) induced an improvement in ethanol production, compared with an identical strain not integrating the Calvin cycle (RbcX+(GroES+GroEL) E. coli). The yield of ethanol produced from glucose consumed is thus improved by 7% (0.49 g/g vs. 0.46 g/g), to the detriment of biomass yield (0.035 vs. 0.051 g/g), suggesting marked redistribution of carbon toward ethanol production.

(89) TABLE-US-00011 TABLE XI Production yields of ethanol and biomass during anaerobic cultures (Prk: phosphoribulokinase) Yields Genotype Biomass Ethanol RuBisCO PRK Chaperones g/g g/g + 0.051 0.46 + + + 0.035 0.49
4.2. Study of RuBisCO Complex Functionality In Vivo

(90) Experimental Protocol

(91) Precultures were prepared on chemically defined medium. After thawing, 1 ml of a stock tube (80 C.) was taken to inoculate a penicillin bottle (100 ml) containing 10 ml of culture medium (including 0.1 g/l formic acid supplemented with 20 g/l glucose), incubated for 18 hours at 30 C. and 120 rpm. The precultures were prepared in anaerobiosis (bottles previously flushed with nitrogen) and in the presence of doxycycline (2/ml) in order to avoid the toxicity problems observed in the presence of the PRK gene.

(92) The precultures were then washed three times (centrifugation, resuspension, vortex for 15 s) with physiological saline (NaCl, 9 g/l), then the cell pellet was resuspended in culture medium without doxycycline.

(93) These cells stemming from the precultures were then inoculated in culture medium containing 0.5 g/l formic acid and 0.5 g/l glucose. The starting culture volume was 25 ml (250 ml baffled Erlenmeyer flasks).

(94) The various yeast strains are grown on .sup.13C-labeled or unlabeled formate supplemented or not supplemented with unlabeled glucose. To demonstrate incorporation of the carbon isotope from formate, the isotopic composition of a stable cellular metabolite, ergosterol, is analyzed. The cell cultures were centrifuged for 5 min at 10000 rpm and the pellet resuspended in 7 ml of chloroform/methanol (2:1) and centrifuged for 5 min at 10000 rpm. The supernatant is supplemented with 2 ml of TE, and after centrifugation for 5 min at 10,000 rpm the chloroform phase is collected and evaporated under a stream of nitrogen. The residue is resuspended in 500 l of methanol. The samples are analyzed by high-performance liquid chromatography (HPLC) on a chromatograph (Waters, Alliance 2690) equipped with an Aminex HPX 87-H.sup.+ (300 mm7.8 mm) column.

(95) Results

(96) As CO.sub.2 transport in yeast from the outside to the inside of the cell is not a natural process, and awaiting a complementary engineering making it possible to establish same by co-expression of a transporter such as the specialized aquaporins described in S. elongatus, formic acid able to be oxidized by yeast dehydrogenase into carbon dioxide was used as intracellular carbon dioxide source. This carbon dioxide can potentially be reincorporated into organic materials through the RuBisCO complex. Thus, in the presence of .sup.13C labeled formate, incorporation of the isotope into biomass is expected. Nevertheless, the existence of other anaplerotic natural reactions (capable of fixing CO.sub.2) in yeast explains why under these conditions one observes significant background noise from .sup.13C incorporation (about 3-4% of labeling) even in the absence of RuBisCO complex, making ambiguous the interpretation of the contribution of RuBisCO in the isotope incorporation observed. An analysis of metabolic pathways shows that the conditions used in this first experiment are in fact not suited to isotopic measurement of RuBisCO activity in vivo. It should be noted that this experiment made it possible nevertheless to confirm that the absence of incorporation in vivo of labeled bicarbonate when it is added to the culture medium using glucose and not formate as carbon source is indeed due to a problem of CO.sub.2 (or bicarbonate/carbonate) transport and not to a metabolic problem.

(97) Consequently, our attention is drawn to other evidence of proof of concept such as kinetics of formic acid consumption and maintenance of viability of strains carrying or not carrying the engineering. It should be noted that the use of formic acid as sole carbon source does not enable the strain to grow because of insufficient energy resources, at least in the absence of supplemental engineering of formate dehydrogenases. Only maintenance of viability is observable under these conditions. This energy balance can nevertheless be improved by adding a small amount of glucose.

(98) Use of Formate as Carbon Source

(99) Aerobic cultures on formic acid (0.45 g/l) and glucose (0.55 g/l) were used to characterize phenotypically strains containing the complete CARBOYEAST engineering or isolated elements so as to characterize growth on formic acid. Formic acid can be metabolized in yeast to CO.sub.2 and reducing power (H.sub.2) by formate dehydrogenase, nevertheless yeast is not able to grow on formic acid as sole carbon source.

(100) FIG. 12 shows that, during aerobic cultures, the complete CARBOYEAST engineering (CEN.PK no. 3: RbcS+RbcL+PRK+RbcX+(GroES+GroEL) E. coli) induced complete consumption of formic acid, compared with an identical strain lacking PRK (CEN.PK no. 2: RbcS+RbcL+RbcX+(GroES+GroEL) E. coli), not allowing the production of substrate for RuBisCO. In parallel, an improvement in biomass production is observed, whereas glucose consumption remains identical. The strain having the complete engineering thus has a better capacity to transform formic acid.

(101) 4.3. Introduction in Yeast of a RuBisCO-Dependent Calvin Cycle Modifies In Vivo the Equilibrium of Biosynthetic Pathways in Central Metabolism

(102) The object of this study is to show that the introduction of a Calvin cycle in yeast by functional co-expression of RuBisCO (and chaperones) and phosphoribulokinase significantly modifies the internal metabolic profile in a direction compatible with the functionality of the engineering in vivo. This metabolic profile was evaluated after culture of strains carrying a complete or only partial engineering and comparative analysis of the phosphometabolome by mass spectrometry coupled to HPLC (ion-pairing reversed-phase chromatography).

(103) The strains tested are: The strain containing the complete engineering (CEN.PK no. 3) and that lacking PRK (CEN.PK no. 2). The cells are grown at 30 C. in ambient air with shaking on YNB (yeast without nitrogen base) medium, supplemented with 6.7 g/l ammonium sulfate, 20 g/l glucose, 20 g/l agar for the agars) with commercial CSM medium (MP Biomedicals), and suited to the selection markers of the plasmids used (medium without leucine, uracil and tryptophan). The cultures are stopped by cooling at 4 C. a generation before the end of the exponential phase. The analysis is carried out on protein extractions stemming from 1 ml of cells in exponential growth phase quenched with 5 ml of 80% (v/v) methanol/water+10 mM AcNH.sub.4. After centrifugation, the pellet is stored at 80 C. The extraction is carried out by suspending the pellet in 5 ml of 75% (v/v) ethanol/water, 10 mM AcNH.sub.4 with extemporaneous addition of 150 l of a mixture of pure metabolite standards labeled with .sup.13C (IDMS method). After incubation for 5 min at 80 C. and rapid cooling in a liquid nitrogen bath, centrifugation is used to remove the debris.

(104) The IDMS method is used for absolute quantification. In the context of this analysis, absolute quantification of ribulose-1,5-bisphosphate could not be obtained due to the lack of availability of an adequate standard and was replaced by a non-isotopic external calibration which nevertheless allows an estimate (probably underestimated) of the concentration of this compound in yeast.

(105) The results, presented in FIG. 13, suggest the re-equilibration of synthetic pathways within the cell taking into account the reconstituted Calvin cycle, which can be summarized by the metabolic simulation of FIG. 14.