# Patent

## Title
Metabolically enhanced cyanobacterium with sequentially inducible production genes for the production of a first chemical compound

## Abstract

This invention provides a method for the prolonged production of ethanol using a metabolically enhanced cyanobacterium.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. Non-Provisional application Ser. No. 14/320,477, filed Jun. 30, 2014, now U.S. Pat. No. 9,315,820, which is a continuation of International Application No. PCT/EP2012/076786, filed Dec. 21, 2012, which claims priority to U.S. Provisional Application No. 61/583,580, filed Jan. 5, 2012, and also claims priority to U.S. Provisional Application No. 61/581,976, filed Dec. 30, 2011, all of which are incorporated herein by reference.


STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable.
REFERENCE TO SEQUENCE LISTING
This application contains a sequence listing submitted by EFS-Web, thereby satisfying the requirements of 37 C.F.R. §§1.821-1.825. The sequence listing, created on Jun. 30, 2014, contains 84 sequences and is 486 KB in size.
FIELD OF THE INVENTION
This invention is related to the field of production of chemical compounds by using metabolically enhanced cyanobacterial cells.
BACKGROUND OF THE INVENTION
Various chemical compounds of interest, such as biofuels like fatty acid esters or alcohols, functional foods, vitamins, pharmaceuticals such as lactams, peptides and polyketides or terpenes and terpenoids and also biopolymers such as polyhydroxyalkanoates can be produced via metabolically enhanced cyanobacteria. One of these compounds is ethanol. In this context, the PCT patent application WO 2009/098089 A2 discloses the use of ethanologenic genes, for example pyruvate decarboxylase and alcohol dehydrogenase for the production of ethanol.
Typically, the cyanobacterial host cells for the production of a specific chemical compound of interest are metabolically enhanced hybrid lines, which have been transformed with genetic elements containing corresponding production genes under the control of either constitutive or inducible promoters. In the case of inducible promoters, transcription of the production genes is coupled to specific induction conditions, for instance the addition or depletion of certain metals such as Cu, Zn etc. to, or from, the culture medium.
It is a known problem in the art that such metabolically enhanced cyanobacteria produce such chemical compounds, e g ethanol, for a certain period of time, before the productivity decreases due to mutations in the respective production genes. For example, Takahama and colleagues (2003) investigated the time-related productivity of a recombinant Synechococcus elongatus PCC 7942 harboring a heterologous gene for an ethylene-forming enzyme. They found that the rate of ethylene production in the recombinant culture decreased as a result of competition with faster growing ethylene-non-forming mutants that carried short nucleotide insertions within the coding sequence of the gene for the ethylene forming enzyme.
Therefore, there is a need for improved cyanobacterial hybrid strains for prolonged production of first chemical compounds.
This task is solved by providing a metabolically enhanced cyanobacterium according to base claim 1. Further claims are directed to advantageous embodiments of the metabolically enhanced cyanobacteria, to a method of producing the metabolically enhanced cyanobacteria, and to a method of producing a first chemical compound by culturing the metabolically enhanced cyanobacteria.
SUMMARY OF THE INVENTION
The invention described herein discloses a metabolically enhanced cyanobacterium for the production of a first chemical compound, comprising:

    
    
        at least two first production genes encoding first biocatalysts for the production of the first chemical compound;
        wherein one of the two first production genes is under the transcriptional control of a first promoter for the first production gene;
        wherein the other of the two first production genes is under the transcriptional control of a second promoter for the first production gene;
        wherein the first promoter and second promoter are separately inducible under different conditions;
        wherein the at least two first biocatalysts catalyze the same chemical reaction.
    
    


This invention further discloses a method for producing a metabolically enhanced cyanobacterium as above, comprising the method steps of:

    
    
        a) Providing the following at least two transformable nucleic acid sequences:
        
            said first production gene under the transcriptional control of said first promoter for the first production gene;
            said first production gene under the transcriptional control of said second promoter for the first production gene;
        
        
        b) Transforming said at least two transformable nucleic acid sequences into the cyanobacteria cells.
    
    


This invention also discloses a method for producing a first chemical compound using any of the metabolically enhanced cyanobacterium as above, comprising the method steps of:

    
    
        A) Culturing the metabolically enhanced cyanobacterium under conditions for induction of the first promoter for the first production gene, the cyanobacterium producing the first chemical compound;
        B) Culturing the metabolically enhanced cyanobacterium under conditions for induction of the second promoter for the first production gene, the cyanobacterium producing the first chemical compound;
        
            wherein method step A) and method step B) are temporally separated;
            wherein the second promoter for the first production gene of method step B) is maintained in an uninduced state during method step A).
        
        
    
    


This invention further discloses a metabolically enhanced cyanobacterium for the production of a first chemical compound, comprising:

    
    
        at least a first and second first production gene encoding first biocatalysts for the production of the first chemical compound;
        wherein both first production genes are under the transcriptional control of the same inducible promoter for the first production genes;
        wherein the inducible promoter for the first production genes is gradually inducible in a dose-dependent manner;
        wherein said first biocatalysts catalyze the same chemical reaction.
    
    


Further, this invention discloses a method for producing a first chemical compound using any of the metabolically enhanced cyanobacteria above, comprising the method steps of:

    
    
        A1) Culturing the metabolically enhanced cyanobacterium under a first condition for induction of the promoter for the first production genes, the cyanobacterium producing the first chemical compound;
        A2) Culturing the metabolically enhanced cyanobacterium under a second condition for induction of the promoter for the first production genes, the cyanobacterium producing the first chemical compound;
        
            wherein method step A1) and method step A2) are temporally separated;
            wherein the first condition for induction results in a lower induction of the promoter for the first production genes than the second condition of induction.
        
        
    
    


In another embodiment, a method for producing ethanol from a photoautotrophic cyanobacterium modified to produce ethanol is provided, by

    
    
        A) culturing the photoautotrophic cyanobacterium having at least one recombinant alcohol dehydrogenase gene, a first recombinant pyruvate decarboxylase gene under the control of a first inducible promoter, and a second recombinant pyruvate decarboxylase gene under the control of a second inducible promoter, under conditions for induction of the first inducible promoter, where the photoautotrophic cyanobacterium produces ethanol; and
        B) culturing the photoautotrophic cyanobacterium under conditions for induction of the second inducible promoter, where the photoautotrophic cyanobacterium produces ethanol; where method step A) and method step B) are temporally separated, and where the second inducible promoter is maintained in a substantially uninduced state during method step A).
    
    


The recombinant alcohol dehydrogenase genes can be operably linked, for example, to the recombinant pyruvate decarboxylase genes to form functional operons. The first and second inducible promoters can be chosen from, for example, PntcA, PnblA, PisiA, PpetJ, PpetE, PggpS, PpsbA2, PpsaA, PsigB, PlrtA, PhtpG, PnirA, PnarB, PnrtA, PhspA, PclpB1, PhliB, PcrhC, ziaR-PziaA, smtB-PsmtA, corR-PcorT, nrsRS-PnrsB, nrsRS-PnrsB916, aztR-PaztA, bxmR-PbmtA, bxaR-PbxaI, zntR-PzntA, czrR-PczrB, and nmtR-PnmtA. In an embodiment, at least some of the recombinant genes can be located on at least one extrachromosomal plasmid. The alcohol dehydrogenase gene can be, for example, under the transcriptional control of a different promoter than the first and second pyruvate decarboxylase genes. The at least one alcohol dehydrogenase gene can be, for example, under the control of a constitutive promoter. The first and second inducible promoters can be inducible, for example, by different concentrations of a first inducing agent. The first and second inducible promoters can be, for example, zinc-inducible promoters. the first and second inducible promoters can be, for example, slight nucleic acid sequence variants of the same promoter. the first and second inducible promoters can have, for example, a sequence identity of at least 90%.
In yet another embodiment, a method for producing ethanol from a photoautotrophic cyanobacterium modified to produce ethanol is provided, by

    
    
        A) culturing the photoautotrophic cyanobacterium having at least two ethanologenic gene cassettes located at different locations in the genome, having a recombinant alcohol dehydrogenase gene and a recombinant pyruvate decarboxylase gene, where the promoters regulating the pyruvate decarboxylase gene of the at least two ethanologenic gene cassettes are identical, gradually-inducible promoters, under conditions for a low level of promoter induction, where the photoautotrophic cyanobacterium produces ethanol for several weeks;
        B) thereafter, after either ethanol productivity or pyruvate decarboxylase enzyme activity declines, culturing the photoautotrophic cyanobacterium under conditions for a higher level of promoter induction than in step A), where the photoautotrophic cyanobacterium continues to produce ethanol, where ethanol production in the culture is maintained for a longer period of time than with step A) alone. The gradually-inducible promoter can be inducible, for example, by zinc or cobalt.
    
    





BRIEF DESCRIPTION OF THE FIGURES
The following figures schematically show, inter alia, several maps of plasmids used in representative embodiments of the present invention. Some of these plasmids harbour only one first production gene under the transcriptional control of an inducible promoter for the first production gene, for example the plasmids shown in FIGS. 7-9, 14-16 and 19. The use of one of these plasmids for generating a metabolically enhanced cyanobacterium according to the present invention therefore requires that at least a second first production gene under the transcriptional control of a second inducible promoter for the first production gene is present in the cyanobacteria, e.g. on a different genetic element, to obtain a metabolically enhanced cyanobacterium according to the present invention.
In contrast, some other plasmids harbor already two first production genes under the transcriptional control of a first and a second inducible promoter for the first production gene according to the present invention, for instance plasmids shown in FIGS. 10, 17 and 18. For production of ethanol as the first chemical compound, however, the corresponding metabolically enhanced cyanobacteria have to comprise at least one second production gene encoding an alcohol dehydrogenase enzyme located on another genetic element in addition to the first production genes encoding pyruvate decarboxylases shown in FIGS. 10, 17 and 18.
Plasmid maps shown in the following include restriction sites for the correspondingly denoted restriction endonucleases. “Gm” denotes a gene conferring resistance to Gentamycin, and “aph (KanR2)” denotes a gene coding for aminoglycoside (3′) phosphotransferase conferring resistance to Kanamycin. “Sp/Sm” designates a gene imparting resistance for spectinomycin/streptomycin and “Cm” depicts a gene conferring resistance to Chloramphenicol. The bold circumferential arrows in the plasmid maps illustrate the position and the orientation of inserted genes. Note that the regulator genes generally run in antisense orientation from 3′ to 5′. The protruding angled arrows illustrate the position of the specified promoter sequence.
In general, plasmids were generated by inserting DNA constructs comprising the promoters and the production genes into the plasmids pVZ322a, pVZ324 and pVZ325a as well as pGEM via the multiple cloning site using corresponding restriction/ligation protocols. The shown plasmids can, however, alternatively be synthetically produced by gene synthesis.
FIG. 1A and FIG. 1B schematically illustrate the problem of genetic instability and the corresponding decrease of production of the first chemical compound under long-term cultivation conditions using conventional cyanobacterial hybrid strains. FIG. 1A schematically shows a metabolically enhanced cyanobacterial cell. FIG. 1B shows the same metabolically enhanced cyanobacterial cell after long term cultivation.
FIG. 2A schematically shows a metabolically enhanced cyanobacterial cell according to the principles of the present invention, wherein the production genes are co-located on one genetic element prior to, or at the start of, method step A).
FIG. 2B shows the cyanobacterial cell with the production genes co-located on one genetic element in the transition phase from method step A) to method step B).
FIG. 2C shows the cyanobacterial cell with the production genes co-located on one genetic element in the transition phase from method step B) to method step C).
FIG. 3A schematically illustrates a metabolically enhanced cyanobacterium according to the principles of the present invention, wherein the different production genes are located on different genetic elements, prior to, or at the start of, method step A).
FIG. 3B shows the cyanobacterial cell with the different production genes located on different genetic elements in the transition phase from method step A) to method step B).
FIG. 3C shows the cyanobacterial cell with the different production genes located on different genetic elements in the transition phase from method step B) to method step C).
FIG. 4 illustrates the chosen integration site for homologous recombination of genetic constructs into the endogenous plasmid pAQ4, and a previously published integration site into the endogenous plasmid pAQ3 of Synechococcus PCC7002/ABCC 1535 via recombined flanking regions FA and FB.
FIG. 5 illustrates the chosen integration site for homologous recombination of genetic constructs into the endogenous plasmid pAQ1 of Synechococcus PCC7002 via recombined flanking regions FA2 and FB2.
FIG. 6 illustrates the generation of a transformable genetic construct harboring an operon comprising a first production gene encoding a Pdc enzyme and a second production gene enoding an Adh enzyme under the control of an inducible promoter as well as an antibiotic resistance cassette C.K3. The construct is ligated into the cloning vector pGEM-TK in between flanking regions FA and FB, amplified, cut-out at restriction sites NsiI and SpeI to incorporate the flanking regions and can then be transformed via homologous recombination into e.g. pQ4, pAQ3 or pAQ1 depending on the chosen flanking regions.
FIG. 7A depicts the map of construct #1145 for chromosomal integration comprising a pdc gene from Zymomonas mobilis under the transcriptional control of the Zn2+-inducible promoter ziaR-PziaA and a degenerated adh from Synechocystis PCC 6803 under the transcriptional control of the constitutive promoter Prbc.
FIG. 7B shows the ethanol production per OD of Synechocystis PCC 6803 strain #1145 after induction with Co, Ni or Zn as well as a control without addition of these metal ions.
FIG. 8A depicts the map of the self-replicating broad host range vector pVZ325 #1217 comprising a pdc from Zymomonas mobilis under the transcriptional control of the Co2+-inducible promoter corR-PcorT and a degenerated adh from Synechocystis PCC 6803 under the transcriptional control of the constitutive promoter Prbc*.
FIG. 8B shows the ethanol production per OD750nm of Synechocystis PCC 6803 strain #1217 after induction with Co, Ni or Zn as well as a control without addition of these metals.
FIG. 9A depicts the map of self-replicating broad host range vector pVZ325 #1227 comprising a pdc from Zymomonas mobilis under the transcriptional control of the Ni2+-inducible promoter nrsR-PnrsB and a degenerated adh from Synechocystis PCC 6803 under the transcriptional control of the constitutive promoter Prbc*.
FIG. 9B shows the ethanol production per OD of Synechocystis PCC 6803 strain #1227 after induction with Co, Ni or Zn as well as a control without addition of these metal ions.
FIG. 10A depicts the map of self-replicating broad host range vector pVZ325 #1329 comprising a first production gene encoding a pdc from Zymomobacter palmae under the transcriptional control of the Ni2+-inducible promoter nrsR-PnrsB and a second first production gene encoding a codon-optimised pdc from Zymomonas mobilis under the transcriptional control of the Co2+-inducible promoter corR-PcorT.
FIG. 10B depicts the map of self-replicating broad host range vector pVZ325 #1379 comprising a first production gene encoding a pdc from Zymomobacter palmae under the transcriptional control of the Ni2+-inducible promoter nrsR-PnrsB and a second first production gene encoding a degenerated pdc from Zymomonas mobilis under the transcriptional control of the Co2+-inducible promoter corR-PcorT.
FIG. 11A illustrates the genetic constructs used to generate the Synechocystis PCC 6803 strain #1145/#1329. Strain #1145 harboring a first production gene encoding a pdc enzyme from Zymomonas mobilis under the transcriptional control of the Zn2+-inducible first promoter ziaR-PziaA and a second production gene which is a degenerated adh-gene from Synechocystis PCC 6803 under the transcriptional control of the constitutive Prbc promoter recombined into its chromosome was further transformed with the self-replicating broad host range vector pVZ325 #1329 comprising a second first production gene encoding a Pdc enzyme from Zymobacter palmae under the transcriptional control of the Ni2+-inducible second promoter nrsR-PnrsB and a third first production gene which is a codon-optimised pdc gene from Zymomonas mobilis under the transcriptional control of the Co2+-inducible third promoter corR-PcorT.
FIG. 11B shows the ethanol production per OD of a wild type Synechocystis PCC 6803 transformed with construct #1329 after selective induction with Zn, Co and Ni as well as a control without addition of these metal ions.
FIG. 11C shows the ethanol production per OD of Synechocystis PCC 6803 strain #1145/41329 after selective induction with Zn, Co and Ni as well as a control without addition of these metal ions.
FIG. 12A shows the ethanol production per OD of Synechocystis PCC 6803 strain #1145/#1329 without induction, after induction with Ni2+, after induction with Co2+, and after combined induction with Ni2+ and Co2+.
FIG. 12B shows the ethanol production per OD of Synechocystis PCC 6803 strain #1145/#1329 without induction, after induction with Co2+, after induction with Zn2+, and after combined induction with Zn2+ and Co2+.
FIG. 13 shows the specific Pdc activities of Synechocystis PCC 6803 #1145/#1329 without induction, after selective induction with Zn2+, Zn2++Co2+, and Zn2++Co2++Ni2+.
FIG. 14A depicts the map of construct TK115 for integration into the endogenous pAQ4 plasmid comprising a first production gene encoding a pdc from Zymomonas mobilis under the transcriptional control of the Zn2+-inducible promoter smtB-PsmtA and a degenerated adh-encoding gene from Synechocystis PCC 6803 as second production gene under the transcriptional control of the constitutive promoter Prbc.
FIG. 14B shows the ethanol production per OD of Synechococcus PCC 7002 strain TK115 without induction and after selective induction with Zn, Co or Ni, respectively.
FIG. 15A depicts the map of the self-replicating pVZ325a vector #1217.4 comprising a first production gene encoding a pdc from Zymomonas mobilis under the transcriptional control of the Co2+-inducible promoter corR-PcorT and a degenerated adh-encoding gene from Synechocystis PCC 6803 as second production gene under the transcriptional control of the constitutive promoter Prbc*.
FIG. 15B shows the ethanol production per OD of Synechococcus PCC 7002 strain #1217.4 without induction and after selective induction with Zn, Co or Ni, respectively.
FIG. 16A depicts the map of the self-replicating pVZ325a vector #1356 comprising a first production gene encoding a pdc from Zymobacter palmae under the transcriptional control of the Ni2+-inducible promoter nrsRS-PnrsB* and a degenerated adh-encoding gene from Synechocystis PCC 6803 as second production gene under the transcriptional control of the constitutive promoter Prbc*.
FIG. 16B shows the ethanol production per OD of Synechococcus PCC 7002 strain #1356 without induction and after selective induction with Zn, Co or Ni, respectively.
FIG. 17A depicts the map of self-replicating pVZ325a vector #1375 comprising a first production gene encoding a pdc from Zymobacter palmae under the transcriptional control of the Ni2+-inducible first promoter nrsRS-PnrsB and a second first production gene which is a degenerated pdc-encoding gene from Zymomonas mobilis under the transcriptional control of the Co2+-inducible second promoter corR-PcorT*.
FIG. 17B depicts the map of self-replicating pVZ325a vector #1376 comprising a first production gene encoding a pdc from Zymobacter palmae under the transcriptional control of the Ni2+-inducible first promoter nrsRS-PnrsB* and a second first production gene which is a degenerated pdc-encoding gene from Zymomonas mobilis under the transcriptional control of the Co2+-inducible second promoter corR-PcorT*.
FIG. 18A depicts the map of self-replicating pVZ325a vector #1381 comprising a first production gene encoding a pdc from Zymobacter palmae under the transcriptional control of the Ni2+-inducible first promoter nrsRS-PnrsB and a second first production gene which is a degenerated pdc-encoding gene from Zymomonas mobilis under the transcriptional control of the Co2+-inducible second promoter corR-PcorT.
FIG. 18B depicts the map of self-replicating pVZ325a vector #1383 comprising a first production gene encoding a pdc from Zymobacter palmae under the transcriptional control of the Ni2+-inducible first promoter nrsRS-PnrsB* and a second first production gene which is a degenerated pdc-encoding gene from Zymomonas mobilis under the transcriptional control of the Co2+-inducible second promoter corR-PcorT.
FIG. 19A depicts the map of construct #1389 for integration into the endogenous pSYSG plasmid comprising a first production gene which is a degenerated pdc-encoding gene from Zymobacter palmae under the transcriptional control of the Ni2+-inducible promoter nrsRS-PnrsB.
FIG. 19B depicts the map of self-replicating pVZ324 vector #1391 comprising a first production gene which is a pdc from Zymomobacter palmae under the transcriptional control of the Co2+-inducible promoter corR-PcorT.
FIG. 20A depicts the map of self-replicating broad host range vector pVZ322a with Gm (gentamycin), Cm (chloramphenicol) and aph (kanamycin/neomycin) antibiotic resistance cassettes, based on the RSF1010 plasmid backbone.
FIG. 20B depicts the map of self-replicating broad host range vector pVZ325a with Gm (gentamycin), Cm (chloramphenicol) and Sp/Sm (spectinomycin/streptomycin) antibiotic resistance cassettes, based on the RSF1010 plasmid backbone.
FIG. 21 illustrates the genetic constructs used to generate the Synechocystis PCC 6803 strain #1145/#1391/#1389. Strain #1145 harboring a first production gene encoding a pdc enzyme from Zymomonas mobilis under the transcriptional control of the Zn2+-inducible first promoter ziaR-PziaA and a second production gene which is a degenerated adh-encoding gene from Synechocystis PCC 6803 under the transcriptional control of the constitutive Prbc promoter recombined into its chromosome was further transformed with the self-replicating vector pVZ324 #1391 comprising a second first production gene encoding a pdc enzyme from Zymobacter palmae under the transcriptional control of the Co2+-inducible second promoter corR-PcorT and with the plasmid pSYSG #1389 for integration into the endogenous pSYSG plasmid comprising a third first production gene which is a degenerated gene encoding the pdc enzyme from Zymobacter palmae under the transcriptional control of the Ni2+-inducible third promoter nrsRS-PnrsB.
FIG. 22 illustrates the genetic constructs used to generate the Synechococcus PCC 7002 strain TK115/#1391/TK193. Strain TK115 harboring a first production gene encoding a pdc enzyme from Zymomonas mobilis under the transcriptional control of the Zi2+-inducible first promoter smtB-PsmtA and a second production gene which is a degenerated adh-encoding gene from Synechocystis PCC 6803 under the transcriptional control of the constitutive Prbc promoter recombined into its endogenous pAQ4 plasmid was further transformed with the self-replicating vector pVZ324 #1391 comprising a second first production gene encoding a pdc enzyme from Zymobacter palmae under the transcriptional control of the Co2+-inducible second promoter corR-PcorT and with a further third first production gene which is a degenerated gene encoding the pdc enzyme from Zymobacter palmae under the transcriptional control of the Ni2+-inducible third promoter nrsRS-PnrsB integrated into its endogenous pAQ3 plasmid.
FIG. 23 shows the map of the plasmid TK193 pGEM-AQ3::nrsRS-PnrsB-zpPDC(deg)-Gm designed for integration into the endogenous plasmid pAQ3 of Synechococcus sp. PCC 7002, comprising a first production gene encoding a pdc from Zymobacter palmae under the transcriptional control of the Ni2+-inducible promoter nrsRS-PnrsB. This plasmid is used with other constructs to generate Synechococcus PCC 7002 strain TK115/#1391/TK193.
FIG. 24 depicts the map of construct TK162 pGEM-AQ3::smtB-PsmtA-zmPDC_oop-PrbcL-synADHdeg_oop for integration into the endogenous pAQ3 plasmid of Synechococcus sp. 7002, comprising a first production gene encoding a pdc from Zymomonas mobilis under the transcriptional control of the Zn2+-inducible promoter smtB-PsmtA and a degenerated adh-encoding gene from Synechocystis sp. PCC 6803 as second production gene under the transcriptional control of the constitutive promoter Prbc.
FIG. 25 depicts the map of construct #1233 pGEM-AQ4::smtB-PsmtA-zpPDC-PrbcL*-synADHdeg for integration into the endogenous pAQ4 plasmid of Synechococcus sp. 7002, comprising a first production gene encoding a pdc from Zymomobacter palmae under the transcriptional control of the Zn2+-inducible promoter smtB-PsmtA and a degenerated adh-encoding gene from Synechocystis sp. PCC 6803 as second production gene under the transcriptional control of the constitutive promoter Prbc.
FIG. 26 depicts the map of self-replicating broad host range vector pVZ325a-based construct #1374 pVZ325a-nrsR-PnrsB-zpPDC ter-corR-PcorT*1-zmPDCdeg spf ter for transformation of Synechocystis sp. PCC6803 comprising a first production gene encoding a pdc from Zymomobacter palmae under the transcriptional control of the Ni2+-inducible promoter nrsR-PnrsB and a second first production gene encoding a degenerated pdc from Zymomonas mobilis under the transcriptional control of the Co2+-inducible promoter corR-PcorT*1 construct having an optimised RBS in comparison to the native corR-PcorT.
FIG. 27A schematically illustrates the genetic constructs used to generate the Synechocystis PCC 6803 strain #1145/#1374. Strain #1145 harboring, recombined into its chromosome, a first production gene encoding a pdc enzyme from Zymomonas mobilis under the transcriptional control of the Zn2+-inducible first promoter ziaR-PziaA and a second production gene which is a degenerated adh-gene from Synechocystis PCC 6803 under the transcriptional control of the constitutive Prbc promoter was further transformed with the self-replicating vector pVZ325a #1374 comprising a second first production gene encoding a Pdc enzyme from Zymobacter palmae under the transcriptional control of the Ni2+-inducible second promoter nrsR-PnrsB and a third first production gene which is a codon-degenerated pdc gene from Zymomonas mobilis under the transcriptional control of the Co2+-inducible third promoter corR-PcorT*1.
FIG. 27B shows the specific ethanol production per OD of the metabolically enhanced Synechocystis sp. PCC 6803 strain #1145/#1374 as a function of time after selective induction with Zn, Co and Ni as well as a control without addition of these metal ions.
FIG. 27C illustrates the specific activity of the three different Pdc enzymes of Synechocystis PCC 6803 strain #1145/#1374 in terms of μmol per min and mg protein after selective induction with Ni, Co and Zn in comparison to a control without addition of these metal ions.
FIG. 28A shows the results of culture growth monitoring of Synechocystis PCC 6803 strain #1145/#1374 in 0.5 L photobioreactor scale in terms of culture OD at 750 nm as a function of cultivation time in days during sequential selective induction with Zn2+, Co2+ and Ni2+ of the corresponding Pdc genes.
FIG. 28B shows the results of culture growth monitoring of Synechocystis PCC 6803 strain #1145 in 0.5 L photobioreactor scale in terms of culture OD at 750 nm as a function of cultivation time in days during sequential selective addition of Zn2+, Co2+ and Ni2+ to the culture medium.
FIG. 29A shows the results of ethanol production of Synechocystis PCC 6803 strain #1145/#1374 in 0.5 L photobioreactor scale in % (v/v) as a function of cultivation time in days during sequential selective induction with Zn2+, Co2+ and Ni2+ of the corresponding Pdc genes.
FIG. 29B shows the results of ethanol production of Synechocystis PCC 6803 strain #1145 in 0.5 L photobioreactor scale in % (v/v) as a function of cultivation time in days during sequential selective addition of Zn2+, Co2+ and Ni2+ to the culture medium.
FIG. 30A shows the results of ethanol production of Synechocystis PCC 6803 strain #1145/#1374 in 0.5 L photobioreactor scale in % (v/v) normalised per culture OD at 750 nm as a function of cultivation time in days during sequential selective induction with Zn2+, Co2+ and Ni2+ of the corresponding Pdc genes.
FIG. 30B shows the results of ethanol production of Synechocystis PCC 6803 strain #1145 in 0.5 L photobioreactor scale in % (v/v) normalised per culture OD at 750 nm as a function of cultivation time in days during sequential selective addition of Zn2+, Co2+ and Ni2+ to the culture medium.
FIG. 31A depicts the map of self-replicating broad host range vector pVZ325a-based construct #1460 pVZ325a-nrsRS-PnrsB916-PDCdsrA-Prbc*-synADHdeg for transformation of Synechococcus sp. PCC7002 comprising a first production gene encoding a Pdc from Zymomonas mobilis under the transcriptional control of the Ni2+-inducible promoter nrsRS-PnrsB916 and a degenerated adh-encoding gene from Synechocystis sp. PCC 6803 as second production gene under the transcriptional control of the constitutive promoter Prbc*.
FIG. 31B shows the ethanol production in % (v/v) per OD of Synechococcus sp. PCC 7002 strain #1460 without induction and after selective induction with Zn, Co or Ni, respectively.
FIG. 32 depicts the vector map of construct #1470 pAQ3-corR-PcorT*1-zmPDCdeg_spf-Prbc*-synADHoop for integration into the endogenous pAQ3 plasmid of Synechococcus sp. PCC7002, comprising a codon-degenerated Pdc from Zymomonas mobilis as a first production gene under the transcriptional control of the Co2+-inducible promoter corR-PcorT*1 and an adh-encoding gene from Synechocystis sp. PCC 6803 as second production gene under the transcriptional control of the constitutive promoter Prbc*.
FIG. 33 depicts the vector map of construct #1473 pAQ1::nrsRS-PnrsB193-PDC-PrbcL*-synADH_oop-Sp for integration into the endogenous pAQ1 plasmid of Synechococcus sp. PCC7002, comprising a first production gene encoding Pdc from Zymomonas mobilis under the transcriptional control of the Ni2+-inducible promoter nrsRS-PnrsB193 and an adh-encoding gene from Synechocystis sp. PCC 6803 as second production gene under the transcriptional control of the constitutive Prbc* promoter.
FIG. 34 depicts the vector map of construct #1332 pGEM-AQ4::corR-PcorT-zpPDCter-PrbcL*-synADH_oop-Nm for integration into the endogenous pAQ4 plasmid of Synechococcus sp. PCC7002, comprising a first production gene encoding Pdc from Zymobacter palmae under the transcriptional control of the Co2+-inducible promoter corR-PcorT and an adh-encoding gene from Synechocystis sp. PCC 6803 as second production gene under the transcriptional control of the constitutive PrbcL* promoter.
FIG. 35 depicts the vector map of self-replicating broad host range vector pVZ325-based construct #1627 pVZ326a-PnrsB(ABCC916)-PDC_dsrA-Prbc*(optRBS)-synADHoop-nrsRSBAD(ABCC916) for transformation of Synechococcus sp. PCC7002, comprising a first production gene encoding Pdc from Zymomonas mobilis under the transcriptional control of the Ni2+-inducible promoter PnrsB(ABCC916) along with the nickel-resistance conferring nrsRSBAD gene cluster derived from a Synechococcus species closely related to Synechococcus PCC7002, an adh-encoding gene from Synechocystis sp. PCC 6803 as second production gene under the transcriptional control of the constitutive Prbc* promoter.
FIG. 36A schematically illustrates the metabolic enhancements incorporated in Synechococcus sp. PCC7002 strain TK115/#1470/#1473. The strain harbors a first production gene encoding Pdc from Zymomonas mobilis under the transcriptional control of the Zn2+-inducible promoter smtB-PsmtA and a degenerated adh-gene from Synechocystis sp. PCC6803 under the transcriptional control of the constitutive Prbc promoter integrated into the endogenous plasmid pAQ4, a second first production gene encoding a degenerated pdc from Zymomonas mobilis under the transcriptional control of the Co2+-inducible promoter corR-PcorT*1 and a second production gene which is an adh-gene from Synechocystis sp. PCC6803 under the transcriptional control of the constitutive Prbc* promoter integrated into the endogenous pAQ3 plasmid, and a pdc gene from Zymomonas mobilis as the third first production gene under the transcriptional control of the Ni2+-inducible promoter nrsRS-PnrsB916 as well as an adh-gene from Synechocystis sp. PCC6803 under the transcriptional control of the constitutive Prbc* promoter integrated into the endogenous pAQ1 plasmid.
FIG. 36B shows digital images of agarose gels after electrophoretic analysis of PCR products from amplification of promoter constructs smtB-PsmtA integrated in pAQ4, corR-PcorT integrated in pAQ3 and nrsRS-PnrsB integrated in pAQ1, and combinations thereof, in metabolically enhanced Synechococcus sp. PCC7002 strain TK115/#1470/#1473 and controls.
FIG. 36C shows the results of ethanol production of Synechococcus sp. PCC7002 strain TK115/#1470/#1473 in % (v/v) normalised per culture OD at 750 nm as a function of cultivation time in hours during selective induction with either Zn2+, Co2+ or Ni2+, as well as a control without induction.
FIG. 36D shows the results of ethanol production of Synechococcus sp. PCC7002 strain TK115/#1470 in % (v/v) normalised per culture OD at 750 nm as a function of cultivation time in hours during selective induction with either Zn2+, Co2+ or Ni2+, as well as a control without induction.
FIG. 37A schematically illustrates the metabolic enhancements incorporated in Synechococcus sp. PCC7002 strain #1332/TK162. The strain harbors a first production gene encoding Pdc from Zymobacter palmae under the transcriptional control of the Co2+-inducible promoter corR-PcorT and a second production gene which is an adh-gene from Synechocystis sp. PCC6803 under the transcriptional control of the constitutive Prbc* promoter integrated into the endogenous pAQ4 plasmid, and a second first production gene encoding Pdc from Zymomonas mobilis under the transcriptional control of the Zn2+-inducible promoter smtB-PsmtA and a degenerated adh-gene from Synechocystis sp. PCC6803 under the transcriptional control of the constitutive Prbc promoter integrated into the endogenous plasmid pAQ3.
FIG. 37B shows DNA agarose gel images from PCR analysis for confirmation of successful transformation of Synechococcus sp. PCC7002 hybrid strain #1332/TK162.
FIG. 37C shows the results of ethanol production in % (v/v) per OD of Synechococcus sp. PCC 7002 strain #1332/TK162 without induction and after selective induction with Zn2+ and two different concentrations of Co2+.
FIG. 38A depicts the vector map of construct #1480 pAQ3-aztR-PaztA-zmPDCdeg_spf-Prbc*-synADH_oop for integration into the endogenous pAQ3 plasmid of Synechococcus sp. PCC7002, comprising a degenerated version of the gene encoding Pdc from Zymomonas mobilis under the transcriptional control of the Zn2+-inducible promoter aztR-PaztA (regulator gene/promoter) and an adh-encoding gene from Synechocystis sp. PCC6803 as second production gene under the transcriptional control of the constitutive PrbcL* promoter.
FIG. 38B schematically illustrates the metabolic enhancements incorporated in Synechococcus sp. PCC7002 strain TK115/#1480. The strain harbors a first production gene encoding Pdc from Zymomonas mobilis under the transcriptional control of the Zn2+-inducible promoter smtB-PsmtA and a second production gene which is a degenerated adh-gene from Synechocystis sp. PCC6803 under the transcriptional control of the constitutive Prbc6803 promoter integrated into the endogenous pAQ4 plasmid. The strain further harbors a second first production gene which is a degenerated version of the gene encoding Pdc from Zymomonas mobilis under the transcriptional control of the Zn2+-inducible promoter aztR-PaztA and an adh-gene from Synechocystis sp. PCC6803 under the transcriptional control of the constitutive Prbc* promoter integrated into the endogenous plasmid pAQ3.
FIG. 38C shows DNA agarose gel images from PCR analysis for confirmation of successful transformation of Synechococcus sp. PCC7002 hybrid strain TK115/#1480.
FIG. 38D shows the results of ethanol production in % (v/v) per OD over cultivation time in hours of Synechococcus sp. PCC 7002 strains TK115, #1480 and TK115/#1480 under selective induction with 5 μM Zn2+.
FIG. 38E shows the results of ethanol production in % (v/v) per OD over cultivation time in hours of Synechococcus sp. PCC 7002 strains TK115, #1480 and TK115/#1480 under selective induction with 10 μM Zn2+.
FIG. 39A depicts the vector map of construct #1563 pGEM-gpA::smtB-PsmtA-zmPDC_dsrA-Prbc*-synADH_oop for chromosomal integration in Synechococcus sp. PCC7002 between gene loci A0124 and A0125 (integration site A), comprising a first production gene encoding Pdc from Zymomonas mobilis under the transcriptional control of the Zn2+-inducible promoter smtB-PsmtA (regulator gene/promoter) and an adh-encoding gene from Synechocystis sp. PCC6803 as second production gene under the transcriptional control of the constitutive Prbc* promoter.
FIG. 39B depicts the vector map of construct #1568 pGEM-gpB::smtB-PsmtA-zmPDCdeg_spf-Prbc*-synADH_oop for chromosomal integration in Synechococcus sp. PCC7002 between gene loci A1330 and A1331 (integration site B), comprising a degenerated version of the gene encoding Pdc from Zymomonas mobilis as a first production gene under the transcriptional control of the Zn2+-inducible promoter smtB-PsmtA (regulator gene/promoter) and an adh-encoding gene from Synechocystis sp. PCC6803 as second production gene under the transcriptional control of the constitutive Prbc* promoter.
FIG. 39C depicts the vector map of construct #1692 pGEM-gpC::smtB-PsmtA-zmPDC_oop-PrbcL-synADHdeg_oop for chromosomal integration in Synechococcus sp. PCC7002 between gene loci A2578 and A2579 (integration site C), comprising a first production gene encoding Pdc from Zymomonas mobilis under the transcriptional control of the Zn2+-inducible promoter smtB-PsmtA (regulator gene/promoter) and a degenerated version of the adh-encoding gene from Synechocystis sp. PCC6803 as second production gene under the transcriptional control of the constitutive PrbcL promoter.
FIG. 40A schematically illustrates chromosomal integration sites A-C for constructs #1563, #1568 and #1692 in Synechococcus sp. PCC7002, each construct harbouring a Pdc gene under the transcriptional control of the same Zn2+-inducible promoter smtB-PsmtA.
FIG. 40B shows DNA agarose gel images from PCR analysis for confirmation of successful transformation of Synechococcus sp. PCC7002 hybrid strain 1563/#1568/#1692.
FIG. 40C shows the results of ethanol production in % (v/v) per OD over cultivation time in hours of Synechococcus sp. PCC 7002 strain #1563 under selective induction with 5 μM Zn2+ and 10 μM Zn2+.
FIG. 40D shows the results of ethanol production in % (v/v) per OD over cultivation time in hours of Synechococcus sp. PCC 7002 strain #1568 under selective induction with 5 μM Zn2+ and 10 μM Zn2+.
FIG. 40E shows the results of ethanol production in % (v/v) per OD over cultivation time in hours of Synechococcus sp. PCC 7002 strain #1563/#1568 under selective induction with 5 μM Zn2+ and 10 μM Zn2+.
FIG. 40F shows the results of ethanol production in % (v/v) per OD over cultivation time in hours of Synechococcus sp. PCC 7002 strain #1563/#1568/#1692 under selective induction with 5 μM Zn2+ and 10 μM Zn2+.
FIG. 41A shows the vector map of construct #1564 pGEM-gpA::corR-PcorT-zmPDC_dsrA-Prbc*synADH_oop for chromosomal integration in Synechococcus sp. PCC7002 between gene loci A0124 and A0125 (integration site A), comprising a first production gene encoding Pdc from Zymomonas mobilis under the transcriptional control of the Co2+-inducible promoter corR-PcorT (regulator gene/promoter) and an adh-encoding gene from Synechocystis sp. PCC6803 as second production gene under the transcriptional control of the constitutive Prbc* promoter.
FIG. 41B shows the vector map of construct #1633 pGEM-gpB::corR-PcorT*1-zmPDCdeg_spf-Prbc*-synADH_oop for chromosomal integration in Synechococcus sp. PCC7002 between gene loci A1330 and A1331 (integration site B), comprising a degenerated version of the gene encoding Pdc from Zymomonas mobilis as a first production gene under the transcriptional control of the Co2+-inducible promoter corR-PcorT (regulator gene/promoter) and an adh-encoding gene from Synechocystis sp. PCC6803 as second production gene under the transcriptional control of the constitutive Prbc* promoter.
FIG. 41C shows the vector map of construct #1574 pGEM-gpC::corR-PcorT-zpPDCter-Prbc*-synADHdeg_oop for chromosomal integration in Synechococcus sp. PCC7002 between gene loci A2578 and A2579 (integration site C), comprising a first production gene encoding Pdc from Zymobacter palmae under the transcriptional control of the Co2+-inducible promoter corR-PcorT (regulator gene/promoter) and a degenerated version of the adh-encoding gene from Synechocystis sp. PCC6803 as second production gene under the transcriptional control of the constitutive Prbc* promoter.
FIG. 42A schematically illustrates chromosomal integration sites A-C for constructs #1564, #1633 and #1574 in Synechococcus sp. PCC7002, each construct harbouring a different Pdc gene under the transcriptional control of the same Co2+-inducible promoter corR-PcorT.
FIG. 42B shows DNA agarose gel images from PCR analysis for confirmation of successful transformation of Synechococcus sp. PCC7002 hybrid strain #1564/#1633/#1574.



DESCRIPTION OF THE INVENTION
The first aspect of the invention provides a metabolically enhanced cyanobacterium for the production of a first chemical compound, comprising:

    
    
        at least two first production genes encoding first biocatalysts for the production of the first chemical compound;
        wherein one of the two first production genes is under the transcriptional control of a first promoter for the first production gene;
        wherein the other of the two first production genes is under the transcriptional control of a second promoter for the first production gene;
        wherein the first promoter and second promoter are separately inducible under different conditions;
        wherein the at least two first biocatalysts catalyze the same chemical reaction.
    
    


The use of a first and a second promoter for the first production gene allows for the first biocatalyst under the control of said first promoter to be expressed whereas at the same time the first biocatalyst under the control of the second promoter is not expressed, and vice versa. When the first promoter is induced, the first biocatalyst is expressed and the first chemical compound is produced, whereupon genetic alterations can occur in the corresponding first production gene. At the same time, the second promoter for the first production gene is maintained in an uninduced state and the corresponding second of the first biocatalysts is not expressed, thus better preserving the genetic integrity of the corresponding non-induced first production gene compared to the induced one.
Definitions and General Explanations
The following explanation of terms and methods are provided to better describe the present invention disclosure and to guide those of ordinary skill in the art in the understanding, interpretation and practice of the present invention. Unless explained otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. The materials, methods and examples are illustrative only and not intended to be limiting. Other features and/or embodiments of the invention disclosure are apparent from the detailed description and the claims.
As used herein, the term “comprising” means “including”. The singular forms “a” or “an” or “the” expressly include the plural references unless the context clearly dictates otherwise. Referring to “at least one” or “at least two” object(s) expressly includes additional objects falling into the specification of said at least one or at least two objects according to the present invention. For example, “at least two first production genes” can also include a third or further additional first production gene used inventively according to the criteria of the present invention.
Database entry numbers given in the following are from the NCBI database (National Center for Biotechnology Information; available on the world wide web at ncbi.nlm.nih.gov) or from the CyanoBase, the genome database for cyanobacteria (available on the world wide web at bacteria.kazusa.or.jp/cyanobase/index.html); Yazukazu et al. “CyanoBase, the genome database for Synechocystis sp. Strain PCC6803: status for the year 2000”, Nucleic Acid Research, 2000, Vol. 18, page 72.)
The EC numbers cited throughout this patent application are enzyme commission numbers which is a numerical classification scheme for enzymes based on the chemical reactions which are catalyzed by the enzymes.
A promoter that is gradually inducible in a dose-dependent manner is a promoter that results in an inductor dose dependent expression of the corresponding promoter-controlled production gene.
As used herein, the term “metabolically enhanced” refers to any change in the endogenous genome of a wild type cyanobacterial cell or to the addition of endogenous and non-endogenous, exogenous genetic code to a wild type cyanobacterial cell, for example the introduction of a heterologous gene. More specifically, such changes are made by the hand of man through the use of recombinant DNA technology or mutagenesis. The changes can involve protein coding sequences or non-protein coding sequences in the genome such as regulatory sequences, non-coding RNA, antisense RNA, promoters or enhancers. Aspects of the invention utilize techniques and methods common to the fields of molecular biology, microbiology and cell culture. Useful laboratory references for these types of methodologies are readily available to those skilled in the art. See, for example, Molecular Cloning: A Laboratory Manual (Third Edition), Sambrook, J., et al. (2001) Cold Spring Harbor Laboratory Press; Current Protocols in Microbiology (2007) Edited by Coico, R., et al., John Wiley and Sons, Inc.; The Molecular Biology of Cyanobacteria (1994) Donald Bryant (Ed.), Springer Netherlands; Handbook Of Microalgal Culture: Biotechnology And Applied Phycology (2003) Richmond, A. (ed.), Blackwell Publishing; and “The cyanobacteria, Molecular Biology, Genomics and Evolution”, Edited by Antonia Herrero and Enrique Flores, Caister Academic Press, Norfolk, U K, 2008.
It is well known to a person of ordinary skill in the art that large plasmids can be produced using techniques such as the ones described in the U.S. Pat. No. 6,472,184 B1 titled “method for producing nucleic acid polymers” and U.S. Pat. No. 5,750,380 titled “DNA polymerase mediated synthesis of double stranded nucleic acid molecules”, which are hereby incorporated in their entirety.
Denominations of genes are in the following presented in a three letter lower case name followed by a capitalized letter if more than one related gene exists, for example ziaA for the gene encoding a zinc transporting ATPase. The respective protein encoded by that gene is denominated by the same name with the first letter capitalized, such as ZiaA.
Denominations for promoter sequences, which control the transcription of a certain gene in their natural environment are given by a capitalized letter “P” followed by the gene name according to the above described nomenclature, for example “PziaA” for the promoter controlling the transcription of the ziaA gene.
Denominations for enzyme names can be given in a two or three letter code indicating the origin of the enzyme, followed by the above mentioned three letter code for the enzyme itself, such as SynAdh (Zn2+ dependent alcohol dehydrogenase from Synechocystis PCC6803), ZmPdc (pyruvate decarboxylase from Zymomonas mobilis).
The term “nucleic acid” is intended to include nucleic acid molecules, such as polynucleotides which include an open reading frame encoding a polypeptide, and can further include non-coding regulatory sequences of genes, such as promoters and enhancers as well as non-coding RNAs. In addition, the terms are intended to include one or more genes that are part of a functional operon. In addition, the terms are intended to include a specific gene for a selected purpose. The gene can be endogenous to the host cell or can be recombinantly introduced into the host cell.
In a further embodiment, the invention also provides nucleic acids, which are at least 60%, 70%, 80%, 90% or 95% identical to the promoter nucleic acids or to the nucleic acids encoding either the first or second biocatalysts for the production of the first chemical compound disclosed therein. With regard to the promoters, truncated versions of the promoters including only a small portion of the native promoters upstream of the transcription start point, such as the region ranging from −35 to the transcription start can often be used. Furthermore, introducing nucleotide changes in the untranslated region into the promoter sequence, e.g. into the TATA box, the operator sequence and/or the ribosomal binding site (RBS) can be used to tailor or optimise the promoter for a certain purpose. The invention also provides amino acid sequences for enzymes for the production of the first chemical compounds, which are at least 60%, 70%, 80%, 90% or 95% identical to the amino acid sequences disclosed therein.
In yet a further embodiment, the invention also provides nucleic acids encoding first biocatalysts or second biocatalysts, wherein biocatalysts catalyzing the same chemical reaction are encoded by non-identical gene sequences. The invention provides nucleic acid sequences for biocatalysts catalyzing the same chemical reaction which are less than 80%, 70%, 60% or 50% identical to each other.
The percentage of identity of two nucleic acid sequences or two amino acid sequences can be determined using the algorithm of Thompson et al. (Clustal W, 1994 Nucleic Acid Research 22: pages 4673 to 4680). A nucleotide sequence or an amino acid sequence can also be used as a so-called “query sequence” to perform a nucleic acid or amino acid sequence search against public nucleic acid or protein sequence databases in order to, for example identify further unknown homologous promoters, or homologous protein sequences and nucleic acid sequences which can also be used in embodiments of this invention. In addition, any nucleic acid sequences or protein sequences disclosed in this patent application can also be used as a “query sequence” in order to identify yet unknown sequences in public databases, which can encode for example new enzymes which could be useful in this invention. Such searches can be performed using the algorithm of Karlin and Altschul (1990 Proceedings of the National Academy of Sciences USA 87: pages 2264 to 2268), modified as in Karlin and Altschul (1993 Proceedings of the National Academy of Sciences USA, 90: pages 5873 to 5877). Such an algorithm is incorporated in the Nblast and Xblast programs of Altschul et al. (1990 Journal of Molecular Biology 215, pages 403 to 410) Suitable parameters for these database searches with these programs are, for example, a score of 100 and a word length of 12 for blast nucleotide searches as performed with the Nblast program. Blast protein searches are performed with the Xblast program with a score of 50 and a word length of 3. Where gaps exist between two sequences, gapped blast is utilized as described in Altschul et al. (1997 Nucleic Acid Research, 25: pages 3389 to 3402).
The term “genome” refers to the chromosomal genome as well as to extrachromosomal plasmids which are normally present in the wild type cyanobacterium without having performed recombinant DNA technology. For example, cyanobacteria such as Synechococcus sp. PCC 7002 can include at least up to 6 extrachromosomal plasmids in their wild type form.
The term “biocatalysts” in the following refers to biomolecules which catalyse a chemical reaction. A biocatalyst can be a protein with catalytic activity, e.g. an enzyme, or a nucleic acid with catalytic activity, e.g. a ribozyme.
The use of the term “uninduced state” of a promoter in the following refers to a state where only less than or equal to 20%, preferably less than or equal to 15%, more preferably less than or equal to 10%, most preferred less than or equal to 5% of the first chemical compound per OD750nm (optical density of the cell suspension at 750 nm wavelength as a parameter of cell density) of the cyanobacteria are produced compared to the induced state of said promoter.
Likewise, referring to two or more promoters as being “different” or “separately inducible under different conditions” denotes promoters, wherein conditions for induction of one promoter maintain a second or further promoter in an uninduced state according to the criteria detailed above. The same rule applies to numerated promoters, e.g. first, second, third or further promoters are considered different promoters according the invention and fulfil the specifications detailed above.
The induction factor is defined as the quotient of the production rate of the first chemical compound per OD750nm in the induced state divided by the production rate of the first chemical compound per OD750nm in the uninduced state.
The use of the term “temporally separated” method steps throughout the patent application refers to method steps which are sequentially initiated during the method for producing the first chemical compound. According to the present invention, said sequential initiation requires a change of cultivation conditions, for example for the selective induction of the first, second or further promoter for the first production gene. Said change of cultivation conditions can be decidedly made, either directly or indirectly. Alternatively, said change of cultivation conditions can be inherent to the cultivation, for example due to the consumption of a compound. Said temporal separation of method steps thus stipulates the incorporation of inducible promoters to meet the criteria detailed above for each method step, as opposed for instance to the incorporation of constitutive promoters.
The inventors of the present invention surprisingly found that metabolically enhanced hybrid strains of cyanobacteria can be genetically stably maintained for much longer periods under non-inducing conditions than under induced cultivation conditions. The inventors discovered that under non-inducing conditions when the first biocatalysts, which divert fixed carbon-flux from the metabolic pathways for bacterial growth, are not expressed, the genes encoding these first biocatalysts do not accumulate mutations in contrast to their induced state.
The recurrent problem of such genetic instability of cyanobacterial hybrid strains and the corresponding decrease of the production of the chemical compound is illustrated in FIG. 1. FIG. 1A schematically shows a cyanobacterial hybrid strain as conventionally used for the production of a first chemical compound. The cyanobacterial cell (CB) has been transformed with a vector (VC1), indicated by the circles, carrying a heterologous production gene which is under the transcriptional control of a first inducible promoter, indicated by the horizontal bars on top of the circles, and maintains multiple copies of the vector within one cyanobacterial cell. The large oval in the cyanobacterial cell indicates the bacterial chromosome (CH), whereas the smaller ovals indicate endogenous plasmids (EP). During cultivation, the promoter is induced, driving the expression of the corresponding heterologous production gene, the cyanobacterial cell producing the first chemical compound. In the course of long-term cultivation (FIG. 1B), mutations X (MT1) accumulate in copies of the heterologous production gene, resulting in a decreased expression of functional gene products (e.g. enzymes), thus leading to a decrease of the production of the first chemical compound. At the same time, the revertants grow faster than the metabolically enhanced cyanobacterial cells due to the disposal of the additional metabolic burden that the synthesis of the first chemical compound poses, eventually overgrowing the producing cells.
Due to these mutations in the production genes the metabolically enhanced production strain reverts to the metabolic wild type version, i.e. a strain which is no longer able to produce the first chemical compound. Importantly, these revertants can still carry the selection advantage of, for instance, antibiotic resistance or prototrophy in the case of auxotrophic host strains. For this reason, the revertants exhibit even under selection pressure a significant growth advantage over the first chemical compound-producing metabolically enhanced cyanobacterium strain, since their fixed carbon-flux does not longer bypass anabolic reactions and cell growth for synthesis of the first chemical compound. As soon as this metabolic wild type population overgrows the metabolically enhanced hybrid strain, the productivity in the culture decreases significantly.
The inventors consequently concluded that in order to overcome production decays for the first chemical compound and to prolong the synthesis of the first chemical compound, the solution is a metabolically enhanced cyanobacterial strain, which comprises two or more first production genes, each of which transcriptionally driven by different inducible promoters. Each inducible promoter controls the transcription of an operably linked first production gene and is separately inducible under different conditions. For instance, the metabolically enhanced cyanobacterial hybrid line comprises the first production genes encoding first biocatalysts for the production of the first chemical compound that are under the transcriptional control of a first promoter for the first production gene and a second promoter for the other first production gene, and wherein the first promoter and second promoter are separately inducible under different conditions.
Promoters that are separately inducible under different conditions can for example be promoters that require different inductors for induction. Such promoters can for instance be different metal-ion inducible promoters, e.g. Zn2+, Ni2+ or Co2+ inducible promoters. Alternatively or in addition, such promoters can be inducible by the same inductor but require different concentrations of inductor compared to each other. For instance, the first and second promoter are both Zn2+ inducible promoters, but the first promoter is induced in a concentration range of 1-10 μM Zn2+, whereas the second promoter is induced in a concentration range of 10-20 μM Zn2+, so that conditions for induction of the first promoter can be chosen which maintain the second promoter in an uninduced state according to the definition of the present invention.
Upon the specific induction of the first promoter for the first production gene, the corresponding first biocatalyst directs the metabolic carbon flux of the photoautotrophic cyanobacterium towards the production of the first chemical compound, for instance ethanol. At the same time, the first biocatalyst under the transcriptional control of the second promoter for the first production gene is not expressed and is better preserved from accumulating inactivating genetic alterations. Upon loss of activity of the first biocatalyst following the accumulation of mutations in the first production gene, the second promoter for the first production gene which has not yet accumulated inactivating alterations can be induced, so that the second of the first biocatalysts is expressed which catalyzes the same reaction as the first of the two first biocatalysts, thus leading to a recovery of the production of the first chemical compound and enabling the temporal extension of the production phase of the first chemical compound.
In a preferred embodiment of the invention, the metabolically enhanced cyanobacterium further comprises at least one second production gene encoding a second biocatalyst for the production of the first chemical compound. In such embodiments, the chemical reaction catalyzed by the first biocatalyst is different from the chemical reaction catalyzed by the second biocatalyst. In this case, the first biocatalysts can produce an intermediate, which is further converted by the second biocatalyst to the first chemical compound. In a variant of the metabolically enhanced cyanobacterium, the at least one second production gene is also under the transcriptional control of a first promoter for the second production gene. In some embodiments, said first promoter for the second production gene is inducible under the same conditions as the first promoter for the first production gene. In certain embodiments, the first promoter for the second production gene and the first promoter for the first production gene are the same single promoter.
Cyanobacteria according to certain embodiments of the invention can also comprise a whole sequence of recombinant genes coding for biocatalysts for the production of the first chemical compound in the case that a cascade, for example a series of different enzymes, is necessary to produce the first chemical compound. In particular, the first biocatalyst encoded by the first production gene can produce a first intermediate which is further converted by the second biocatalyst encoded by the second production gene into another second intermediate, which in turn is then further converted by a third biocatalyst encoded by a third production gene into a third intermediate, so that a sequence of consecutive recombinant biocatalysts, which provide intermediates for the next recombinant enzyme for the production of the first chemical compound can be introduced into the cyanobacteria.
In another preferred embodiment, the metabolically enhanced cyanobacterium comprises multiple first production genes, all encoding first biocatalysts catalysing the same chemical reaction, wherein each of the multiple first production genes is under the transcriptional control of a promoter for the first production gene which is separately inducible under different conditions in comparison to the other promoters for the first production gene. In one example, the metabolically enhanced cyanobacterium comprises a further third first production gene under the transcriptional control of a third promoter for the first production gene. In one example, the metabolically enhanced cyanobacterium comprises a fourth first production gene under the transcriptional control of a fourth promoter for the first production gene. In one example, the metabolically enhanced cyanobacterium comprises at least a further fifth first production gene under the transcriptional control of a fifth promoter for the first production gene.
In another preferred embodiment, the metabolically enhanced cyanobacterium comprises more than one second production gene, all encoding second biocatalysts catalysing the same chemical reaction. In one example, the metabolically enhanced cyanobacterium comprises two second production genes, wherein one of the two second production genes is under the transcriptional control of a first promoter for the second production gene and the other of the two second production genes is under the transcriptional control of a second promoter for the second production gene. In another example, the metabolically enhanced cyanobacterium comprises a further third second production gene under the transcriptional control of a third promoter for the second production gene. In another example, the metabolically enhanced cyanobacterium comprises a fourth second production gene under the transcriptional control of a fourth promoter for the second production gene. In another example, the metabolically enhanced cyanobacterium comprises at least a further fifth second production gene under the transcriptional control of a fifth promoter for the second production gene.
In some preferred embodiments, the promoters for the first production genes and the promoters for the second production genes are inducible under the same conditions, so that the first production gene and the second production gene are co-expressed under the same cultivation conditions. This ensures that the first chemical compound can be produced via the enzymatic action of the first and second biocatalyst. In one example, the first promoter for the first production gene and the first promoter for the second production gene are inducible under the same conditions. In another example, also the second promoter for the first production gene and the second promoter for the second production gene are inducible under the same conditions. In yet another example, at least a further third promoter for the first production gene and a further third promoter for the second production gene are inducible under the same conditions.
According to a preferred embodiment of the invention, provided is the metabolically enhanced cyanobacterium with a first production gene and a second production gene which are transcriptionally controlled by the same single promoter. For example, a single first promoter is operably linked with a first production gene and a second production gene to form a functional operon. An operon is a functional unit of DNA which contains a cluster of genes under the control of a single regulatory signal or promoter. Accordingly, both the first production gene and the second production gene of an operon are co-ordinately expressed upon induction of the corresponding promoter. In one example, the metabolically enhanced cyanobacterium comprises one single first promoter controlling the transcription of both the first production gene and the second production gene, thus forming the first operon. In another example, the metabolically enhanced cyanobacterium further comprises one single second promoter controlling the transcription of both a second first production gene and a second production gene, thus forming a second operon. In other examples, the metabolically enhanced cyanobacterium can comprise a third, fourth or further additional operon under the transcriptional control of a third, fourth or further promoter controlling the transcription of a first production gene and a second production gene.
In another preferred embodiment, the metabolically enhanced cyanobacterium comprises a second production gene that is endogenous. In some related examples, wherein the wild type cyanobacterium endogeneously expresses the second biocatalyst that is required and sufficient to convert the intermediate produced by the first biocatalysts into the first chemical compound, the endogenous second production gene can also be non-recombinant, i.e. not affected by any manipulation.
In a further variant, the metabolically enhanced cyanobacterium comprises a second production gene encoding a biocatalyst that catalyzes a chemical reaction that is also present in the wild type cyanobacterium. The inventors surprisingly discovered that under these conditions the genetic stability of the second production gene is much higher compared to the first production gene. Therefore, in some preferred embodiments, the second production gene encoding a biocatalyst that catalyzes a chemical reaction that is also present in the wild type cyanobacterium is under the transcriptional control of a constitutive promoter. The inventors found that the constitutive expression of a second biocatalyst, which catalyzes a chemical reaction also present in the wild type cyanobacterium thereby converting a first intermediate produced by the first biocatalyst into a second intermediate or into the first chemical compound, does not foster the accumulation of mutations in the second production gene.
In yet another preferred embodiment of the invention, the metabolically enhanced cyanobacterium comprises a second production gene that is recombinant. For example, the nucleotide sequence of an endogenous cyanobacterial gene can be altered to form a recombinant second production gene. Such alterations include for instance degenerated variants of a production gene in order to minimise the risk of homologous recombination with other closely related genes in the same strain, which might lead to the inactivation of the gene. In another example, an endogenous cyanobacterial gene is recombinantly put under the transcriptional control of a promoter that is different from the promoter transcriptionally controlling the gene in its native context to form a recombinant second production gene. In a preferred embodiment, a recombinant second production gene comprises an altered nucleotide sequence of an endogenous cyanobacterial gene under the transcriptional control of a promoter that is different from the promoter transcriptionally controlling the gene in its native context.
In some examples, this promoter is a constitutive promoter.
In yet other examples, an endogenous second production gene is operably linked to an inducible promoter to form a recombinant second production gene. In yet another example, an endogenous second production gene is operably linked with a first production gene and an inducible promoter to form part of an operon comprising a recombinant second production gene. In some of these examples, the second production can also be heterologous instead of endogenous. For example, a recombinant second production gene can comprises an altered nucleotide sequence of heterologous gene under the transcriptional control of a promoter, which can in some preferred instances be a constitutive promoter and in some other preferred instances an inducible promoter.
Some preferred embodiments comprise a combination of recombinant and non-recombinant second production genes. For example, additional copies of an endogenous second production gene can be recombinantly introduced into the cyanobacterium to increase the gene copy number. In another example, the cyanobacterial genome harboring an endogenous second production gene can be complemented with one or more additional heterologous second production genes. For instance, cyanobacteria known to endogenously harbor alcohol dehydrogenases could be complemented with a recombinant second production gene encoding an alcohol dehydrogenase enzyme derived from Synechocystis sp. PCC 6803. In preferred related embodiments, recombinant second production genes comprise degenerated versions if one or more endogenous second production gene is present in order to avoid the risk of inactivation by homologous recombination.
In preferred embodiments, the first biocatalyst catalyzes a chemical reaction which is not present in the wild type cyanobacteria. For instance, the introduction of the recombinant first production gene re-directs the metabolic flux of the photoautotrophic cyanobacterium towards the production of the first chemical compound. In preferred embodiments, the first biocatalyst is integrated with the natural metabolism of the cyanobacterium using primary or secondary metabolic products as substrate. In a preferred embodiment, the chemical reaction catalyzed by the first biocatalyst diverts carbon flux for the production of the first chemical compound via pyruvate as a naturally occurring metabolite towards the production of the first chemical compound. In another preferred embodiment, the first biocatalyst diverts carbon flux for the production of the first chemical compound via acetyl-CoA as a naturally occurring metabolite towards the production of the first chemical compound. In yet another preferred embodiment, the first biocatalyst utilizes secondary metabolites from valine biosynthesis and non-mevalonate pathways from valine and isoprenoid synthesis as precursors for the production of the first chemical compound, for example isoprene or isobutanol. In yet another preferred embodiment, the first biocatalyst catalyzes a chemical reaction which diverts acyl-ACP molecules from membrane biosynthesis to produce free fatty acids and alkanes.
In some embodiments, only the at least two first production genes encoding the first biocatalysts are under the transcriptional control of inducible promoters. This is based on the discovery by the inventors that in order to balance cell growth and production of the first chemical compound, and thus improve the genetic stability of the cyanobacterial strain, the control of the metabolic carbon flux of the genetically enhanced cyanobacterium requires only to put such production genes under the control of the inducible promoters that encode biocatalysts catalyzing a chemical reaction that separates the carbon flux from the cell growth and biomass accumulation, respectively, and is not present in the wild type cyanobacterium. If only the first production gene coding for a first biocatalyst catalysing a chemical reaction not present in the wild type cyanobacterium is put under the transcriptional control of a first inducible promoter, the cyanobacterial culture in the uninduced state can accumulate biomass without being prone to inactivating alterations in the first production gene. Only when sufficient biomass is reached, the first production gene will be induced so that a high level of production of the first chemical compound can be achieved.
In a related embodiment, the second biocatalyst catalyzes a chemical reaction which is present in the wild type cyanobacteria and has no influence on the carbon flux as it converts the intermediate produced by the first biocatalyst. In yet another related embodiment, the at least one second production gene encoding the second biocatalyst is under the transcriptional control of a constitutive promoter. The inventors found that a cyanobacterial hybrid strain which is metabolically enhanced according to the embodiments detailed above is less prone to accumulation of mutations in the first and second production genes and allows for a particularly prolonged production of the first chemical compound, for instance ethanol. The inventors concluded that the introduction of additional recombinant copies of biocatalysts which catalyze a chemical reaction present in the wild type cyanobacterium influences the metabolism of the cyanobacterium to a lower extent in the absence of catalytic activity of the first biocatalyst, however, it can also reduce the accumulation of toxic precursors/intermediates, e.g. as it is the case for acetaldehyde if ethanol is produced, in the presence of catalytic activity of the first biocatalyst. If ethanol is produced as the first chemical compound, the first biocatalyst could be a pyruvate decarboxylase, which is not present in wild type cyanobacteria. In contrast to that, most wild type cyanobacteria are known to harbor alcohol dehydrogenases, which could be the second biocatalyst. Accordingly, the at least one second production gene encoding an alcohol dehydrogenase could therefore be put under the transcriptional control of a constitutive promoter.
In some embodiments, the first production genes are co-located on the same genetic element. According to the invention, a genetic element is selected from a group comprising a vector, an endogenous plasmid, a chromosome and combinations thereof. For example, two first production genes, one of the two first production genes under the transcriptional control of a first promoter for a first production gene, the other first production gene under the transcriptional control of a second promoter for the first production gene, respectively, are co-located on the same genetic element. In another example, a third, fourth or further first production gene under the transcriptional control of a third, fourth or further promoter for the first production gene is co-located with said two first production genes on the same genetic element. FIG. 2 shows an exemplary embodiment wherein three first production genes are co-located on the same genetic element. In this example, the cyanobacterial cells (CB) have been transformed with self-replicating vectors (VC123), indicated by the circles, harboring three first production genes, indicated by the three interconnected horizontal bars with different hachures on top of the circles, each of which is under the control of a different inducible promoter. The cyanobacterial cell maintains multiple copies of the vector. The large oval in the cyanobacterial cell indicates the bacterial chromosome (CH), whereas the smaller ovals indicate endogenous plasmids EP). FIG. 2A shows the cyanobacterial cell prior to, or at the beginning of, the cultivation. Upon induction of the first inducible promoter for the first production gene, the corresponding first production genes are expressed and the cyanobacterial cell commences production of the first chemical compound. FIG. 2B shows the situation of the culture after long-term cultivation. Mutations (MT1) have accumulated in the first production genes that have been expressed, indicated by the X in the respective first small horizontal bar depicting the first production genes, consequently leading to a decrease of the productivity of the cyanobacterial culture, as revealed by culture monitoring. At this stage, the second inducible promoter for the second of the first production genes is induced, driving the expression of the second of the first production genes, thus leading to a recovery of the production of the first chemical compound. FIG. 2C depicts the final phase of this example. Mutations (MT2) have now also accumulated in the second of the first production genes, indicated by the X in the respective second small horizontal bar depicting the second first production genes, and the third inducible promoter of the first production gene is now induced in order to recover the production of the first chemical compound. Note that the figures serve illustrative purposes only. It is for example evident to those skilled in the art that the production genes of FIG. 2 could also be harbored by a bacterial chromosome (CH) or one or more endogenous plasmids (EP). Furthermore, said different versions of the first production genes of FIG. 2 could, for instance, be different operons instead, each comprising a first and a second production gene which are operably linked and under the transcriptional control of a single promoter driving the expression of the respective operon. In some embodiments, the at least one second production gene is located on a different genetic element, distinct from the genetic element harboring the first production genes. For instance, the first production genes are co-located on a vector, whereas the at least one second production gene is located on a bacterial chromosome. In another example, the first production genes are co-located on an endogenous plasmid. In yet another example, the first production genes are co-located on a bacterial chromosome. In a typical cyanobacterial cell, a plurality of said genetic elements is present. In certain preferred embodiments, the at least one second production gene is also co-located with the first production genes on the same genetic element. In a related embodiment, said genetic element comprises at least one first production gene which is operably linked with a second production gene and wherein the first and second production gene are under the transcriptional control of one single first promoter to form an operon. In another example, the genetic element comprises one first operon under the transcriptional control of a first promoter and at least one second operon under the transcriptional control of a second inducible promoter. In another embodiment, the genetic element comprises at least one further third operon under the transcriptional control of a third inducible promoter.
In other variants of the invention, said first production genes are located on different genetic elements (FIG. 3). For instance, a metabolically enhanced cyanobacterium (CB) comprises multiple identical copies of a self-replicating vector (VC1), indicated by the circles, harboring a first production gene under the control of the first inducible promoter for the first production gene, indicated by the horizontal bar on top of the circles. The cell has been further transformed with a second first production gene under the transcriptional control of the second inducible promoter for the first production which has been recombined into the bacterial chromosome (CH2), indicated by the horizontal bar on top of the large oval; and a third first production gene under the transcriptional control of the third inducible promoter for the first production gene which has been recombined into several copies of an endogenous plasmid (EP3), indicated by the horizontal bars on top of the small ovals. FIG. 3A shows the metabolically enhanced cyanobacterial strain prior to, or at the start of, the cultivation. Upon induction of the first promoter, the first production gene is expressed, which is in this case located on the vectors (VC1), and the bacterial culture commences production of the first chemical compound. After a certain period of time (FIG. 3B), mutations (MT1) have accumulated in the first production genes driven by the first promoter for the first production genes, indicated by the X, as determined by continuous culture monitoring, thus leading to a decrease of the production of the first chemical compound. In this phase, the second promoter is initiated, driving the expression of the alternative second first production gene on the bacterial chromosome (CH2), thus leading to a recovery of the production of the first chemical compound. In the course of further long-term cultivation (FIG. 3C), mutations (MT2) also accumulate in the second first production gene on the bacterial chromosome, indicated by the X, which is detected by continuous culture monitoring. A final cultivation phase is then initiated by inducing the third promoter for the third first production gene driving the expression of the first production genes located on the endogenous plasmids (EP3). In related embodiments, the at least one second production gene can be either co-located with one or more of the first production genes, or distinct from the first production genes on one or more different genetic element. Said genetic elements are selected from a group comprising a vector, an endogenous plasmid or a bacterial chromosome and combinations thereof. The metabolically enhanced cyanobacterium can comprise multiple copies of one or more of said genetic elements, thus increasing the gene dosage of the first and/or second production genes. In one example, at least one first production gene and one second production gene are operably linked and are under the transcriptional control of one single first inducible promoter to form a first operon. In certain preferred examples, the metabolically enhanced cyanobacterium comprises two or more of said operons, each of which is under the transcriptional control of a different inducible promoter, and wherein said operons are located on different genetic elements. For instance, a first operon is located on a vector, a second operon is located on an endogenous plasmid, and a third operon is located on the bacterial chromosome. In certain examples, the copy number of said operons is increased due to the presence of multiple copies of said genetic elements. The inventors discovered that the genetic stability of a metabolically enhanced cyanobacterium, comprising first production genes that are located on different genetic elements is improved so that cyanobacterial hybrid strains according to the embodiments above allow for a particularly prolonged production of the first chemical compound.
In yet another preferred embodiment, the metabolically enhanced cyanobacterium comprises combinations of first production genes that are co-located on the same genetic element as well as first production genes that located on different genetic elements. For example, the cyanobacterium can comprise two first production genes that are located on the same genetic element, e.g. multiple identical copies of a self-replicating plasmid, and at least a further third first production gene that is located on a different genetic element, e.g. integrated into endogenous plasmids or bacterial chromosomes, as well as combinations thereof if more than a third first production gene is present. As another example, the cyanobacterium comprises two first production genes that are co-located on endogenous plasmids and at least a further third first production gene that is located on the bacterial chromosomes or on a self-replicating plasmid, as well as combinations thereof if more than a third first production gene is present. Likewise, the at least one second production gene can be co-located with at least one of the first production genes, or be located on different genetic elements, as well as combinations thereof if more than one second production gene is present. The inventors found these embodiments are also particularly suitable to counteract genetic instability as well as intramolecular and intermolecular recombination of the production genes compared to the co-location of all first production genes, and thus aid prolonged production of the first chemical compound.
Preferred vectors for the transformation of cyanobacteria comprise for instance self-replicating broad-host range vectors based on RSF1010, such as pVZ and pDAG vectors. In some examples, vectors based on pDU1 can be advantageous. Preferred genetic elements for integration of first and second production genes are for instance the chromosome, and the endogenous cyanobacterial plasmids.
In some preferred embodiments, at least one first production gene is located on at least one type of endogenous plasmid present in cyanobacterial host cells. For instance, in Synechococcus sp. PCC 7002 the inventors found that particularly productive and genetically stable hybrid strains could be produced if at least one of the plasmids pAQ1, pAQ3, pAQ4, pAQ5, pAQ6 and/or pAQ7 was implemented as genetic element to harbor at least one first production gene and/or second production gene. In certain preferred examples, the endogenous plasmids comprise the pAQ4 plasmid, the pAQ3 plasmid and/or the pAQ1 plasmid. In some favourable embodiments, the endogenous plasmid comprises the pAQ4 plasmid. The inventors specifically created a novel integration site for homologous recombination of production genes into pAQ4 (FIG. 4 left). They designed two regions of homology, pAQ4-FA and pAQ4-FB, flanking the respective genetic construct, which recombine with homologous regions in pAQ4 between gene loci SYNPCC7002_D0017 (hypothetical protein, 237 nt, 78 aa) and SYNPCC7002_D0018 (CRISPR-associated protein Cas2, 294 nt, 97 aa). The inventors found particularly good production characteristics of Synechococcus sp. PCC 7002 strains which were metabolically enhanced in this way. In yet other favourable embodiments, the endogenous plasmid comprises the pAQ3 plasmid. The inventors implemented a method described by Xu and colleagues (2011) for homologous recombination of production genes into pAQ3 (FIG. 4 right) and found particularly good production characteristics of Synechococcus sp. PCC 7002 strains which were metabolically enhanced in this way. In yet other favourable embodiments, the endogenous plasmid comprises the pAQ1 plasmid. The inventors modified a method described by Xu and colleagues (2011), to accomplish an improved homologous recombination of production genes into pAQ1 between gene loci SYNPCC7002_B0001 and SYNPCC7002_B0002 (FIG. 5), which leads only to a minor deletion of 57 bp in the plasmid. Synechococcus sp. PCC 7002 strains metabolically enhanced in this way exhibited particularly good production characteristics. In certain related instances, the inventors discovered that the implementation of more than one type of these endogenous plasmids as a carrier for the production gene(s) in the same strain resulted metabolically enhanced hybrid strains with unexpectedly good production properties. For example, a combination comprising the pAQ4 plasmid harboring at least one first production gene with the pAQ3 plasmid harboring at least one further first production gene, in addition to at least one additional genetic element harboring at least one further first production gene, e.g. a self-replicating plasmid, pAQ1 plasmid and/or bacterial chromosome, resulted in Synechococcus sp. PCC 7002 hybrid strains with particularly good production characteristics.
Likewise, the inventors found for Synechocystis sp. PCC 6803 that particularly productive and genetically stable hybrid strains could be produced if at least one type of endogenous plasmid was implemented as genetic element to harbor at least one first production gene and/or second production gene. In certain preferred examples, the endogenous plasmids comprise the pSYSG plasmid endogenous to Synechocystis sp. PCC 6803. For example, the inventors found that metabolically enhanced Synechocystis sp. PCC 6803 comprising the pSYSG plasmid harboring at least one first production gene in addition to at least one additional genetic element harboring at least one further first production gene, e.g. a self-replicating plasmid and/or bacterial chromosome, resulted in hybrid strains with particularly good production characteristics.
In a preferred embodiment, the first biocatalysts and the second biocatalysts are ethanologenic enzymes. For instance, the first production genes encode a pyruvate decarboxylase enzyme catalyzing the reaction from pyruvate to acetaldehyde. In another example, the first production genes encode an AdhE enzyme (alcohol dehydrogenase E) which directly converts acetyl coenzyme A to ethanol. If the first production genes encode an AdhE enzyme, only the first production genes encoding first biocatalysts are required to produce ethanol. In another example, the second production gene encodes an Adh enzyme (alcohol dehydrogenase), catalyzing the reaction from acetaldehyde to ethanol. For instance, the pyruvate decarboxylase enzyme as first biocatalyst catalyzes the conversion of pyruvate to acetaldehyde, whereas the alcohol dehydrogenase Adh enzyme as second biocatalyst catalyzes the further conversion of acetaldehyde to the final first chemical compound ethanol.
Regarding the nucleic acid sequences, protein sequences and properties of these above-mentioned ethanologenic enzymes, reference is made to the PCT patent application WO 2009/098089 A2, which is incorporated for this purpose.
The pyruvate decarboxylase can, for example, be from Zymomonas mobilis, Zymobacter palmae, Sarcina ventriculi or the yeasts Saccharomyces cerevisiae, Pichia pastoris and Klyveromyces lactis. Moreover, pdc enzymes of plant origin like Populus deltroides, Ipomea batatas or Zea mays and pdc enzymes from other host species capable of expression in cyanobacteria can be used.
The Adh enzyme can, for example, be the Adh enzyme from Synechocystis sp. PCC 6803 (SynAdh), a Zn2+ dependent alcohol dehydrogenase such as AdhI from Zymomonas mobilis (ZmAdh), or the Adh from other cyanobacteria. Alternatively or in addition, the enzyme can also be an iron-independent alcohol dehydrogenase (for example AdhII from Zymomonas mobilis). Both native and degenerated Adh enzymes can be used. Degenerated enzymes denote enzymes encoded by gene sequences which have been altered without changing the encoded amino acid sequence. Degenerated gene sequences include for instance changes in the wobble bases in the triplet codon which do not change the amino acid encoded by this triplet. The Zn2+ dependent alcohol dehydrogenase can, for example, be an alcohol dehydrogenase enzyme having at least 60%, 70%, preferably 80% and most preferred 90% or even more than 90% sequence identity to the amino acid sequence of Zn2+ dependent Synechocystis Adh.
Experiments have shown that in particular Synechocystis alcohol dehydrogenase (slr1192) is able to ensure a high ethanol production in metabolically enhanced cyanobacteria due to the fact that the forward reaction, the reduction of acetaldehyde to ethanol is much more preferred for Synechocystis alcohol dehydrogenase enzyme than the unwanted back reaction from ethanol to acetaldehyde. In certain other embodiments, other alcohol dehydrogenase enzymes from other host species can be used that are capable of expression in cyanobacteria.
The AdhE is an iron-dependent, bifunctional enzyme containing a CoA-depending aldehyde dehydrogenase and an alcohol dehydrogenase activity. One characteristic of iron-dependent alcohol dehydrogenases (for example AdhE and AdhII) is the sensitivity to oxygen. In the case of the AdhE from E. coli a mutant was described that shows in contrast to the wild type also Adh activity under aerobic conditions. The site of the mutation was determined in the coding region at the codon position 568. The G-to-A nucleotide transition in this codon results in an amino acid exchange from glutamic acid to lysine (E568K). The E568K derivative of the E. coli AdhE is active both aerobically and anaerobically (Holland-Staley et al., Aerobic Activity of Escherichia coli Alcohol Dehydrogenase is determined by a single amino acid, J Bacteriology 2000, 182, 6049-54). Adh enzymes directly converting acetyl coenzyme A to ethanol can preferably be from a thermophilic source thereby conferring an enhanced degree of stability. The AdhE can be from Thermosynechococchus elongatus BP-1 or also can be a non-thermophilic AdhE enzyme from E. coli. 
The invention further provides biocatalysts catalyzing the same chemical reaction which are encoded by non-identical gene sequences. By this means, multiple versions of e.g. first production genes can be transformed into the cyanobacterial host cell, yet reducing the genes' risk of inactivation via homologous recombination after genetic alterations have occurred in some of these genes. In a related embodiment, such non-identical gene sequences share less than 80%, less than 70%, less than 60% or less than 50% sequence identity, or combinations thereof. Such non-identical sequences comprise, for instance, enzyme isoforms, gene sequences comprising conservative mutations, degenerated sequences comprising codon usage bias based on tRNA wobble bases, and combinations thereof. For example, enzyme isoforms of the first biocatalyst can comprise a pyruvate decarboxylase from Zymomonas mobilis, a second pyruvate decarboxylase from Zymobacter palmae, and a third pyruvate decarboxylase of the yeast Saccharomyces cerevisiae. Non-identical gene sequences comprising conservative mutations denote DNA or RNA sequences wherein a change in the nucleotide sequence leads to the replacement of one amino acid with a biochemically similar one, for instance a glutamic acid for an aspartic acid or an isoleucine for a valine. Gene sequences which are degenerated in order to reduce the risk of homologous recombination include in particular changes in the wobble bases in the triplet codon for the amino acids of the protein encoded by these genes which do not change the amino acid encoded by this triplet (Table 1). For instance, a specific nucleotide in the triplet can be replaced by another nucleotide so that the base triplet still codes for the same amino acid in the first or second biocatalysts. In this context, the term “SynADHdeg” denotes a degenerated DNA sequence having a sequence identity of 61% to the wild type Synechocystis adh gene coding for the Synechocystis sp. PCC 6803 alcohol dehydrogenase enzyme, the terms “zmPDCdeg” and “zpPDCdeg” denote degenerated DNA sequences having a sequence identity of 63.6% and 64.8% to the wild type Zymomonas mobilis pdc and Zymobacter palmae pdc, respectively. In other embodiments, the biocatalysts catalyzing the same chemical reaction can also be encoded by identical gene sequences.







TABLE 1





Codon usage of Synechocystis sp. PCC 6803 implemented to generate degenerated and/or 


codon-optimised gene sequences encoding the first or second production genes.






























UUU
Phe
.60
29
UCU
Ser
.19
11
UAU
Tyr
.45
12
UGU
Cys
.57
5


UUC
Phe
.40
19
UCC
Ser
.37
22
UAC
Tyr
.55
2
UGC
Cys
.43
4


UUA
Leu
.16
17
UCA
Ser
.05
3
UAA
END
.36
2
UGA
END
.24
1


UUG
Leu
.30
33
UCG
Ser
.06
3
UAG
END
.40
2
UGG
Trp
1.00
15


CUU
Leu
.10
11
CCU
Pro
.18
9
CAU
His
.39
7
CGU
Arg
.24
11


CUC
Leu
.16
18
CCC 
Pro
.52
26
CAC
His
.61
11
CGC
Arg
.23
10


CUA
Leu
.09
10
CCA
Pro
.10
5
CAA
Gln
.58
23
CGA
Arg
.07
3


CUG
Leu
.20
22
CCG
Pro
.19
10
CAG
Gln
.42
17
CGG
Arg
.30
14


AUU
Ile
.60
40
ACU
Thr
.21
12
AAU
Asn
.46
16
AGU 
Ser
.17
10


AUC
Ile
.36
24
ACC
Thr
.55
32
AAC
Asn
.54
18
AGC
Ser
.17
10


AUA
Ile
.04
2
ACA
Thr
.09
5
AAA
Lys
.68
28
AGA
Arg
.07
3


AUG
Met 
1.00
27
ACG
Thr
.14
8
AAG
Lys
.32
13
AGG
Arg
.09
4


GUU
Val
.26
20
GCU
Ala
.31
30
GAU
Asp
.60
25
GGU
Gly
.38
29


GUC
Val
.18
14
GCC
Ala
.44
43
GAC
Asp
.40
17
GGC
Gly
.28
21


GUA
Val
.17
13
GCA
Ala
.10
10
GAA
Glu
.75
41
GGA
Gly
.14
11


GUG
Val
.39
30
GCG
Ala
.15
15
GAG
Glu
.25
14
GGG
Gly
.20
15









A variety of suitable cyanobacterial host organisms can be metabolically enhanced to produce the first chemical compound according to the principles of the invention. In preferred embodiments, suitable cyanobacteria include but are not limited to genera of the group comprising Synechocystis, Synechococcus, Anabaena, Chroococcidiopsis, Chlorogloeopsis, Cyanothece, Lyngbya, Phormidium, Nostoc, Spirulina, Arthrospira, Trichodesmium, Leptolyngbya, Plectonema, Myxosarcina, Pleurocapsa, Oscillatoria, Pseudanabaena. Cyanobacterium, Geitlerinema, Euhalothece, Calothrix, Scytonema. In more preferred embodiments, the cyanobacterial host organisms comprise Synechococcus sp. PCC 7002 and other Synechococcus strains, Synechocystis sp. PCC 6803 strains, Chlorogloeopsis strains, and Chroococcidiopsis strains. In particularly preferred embodiments, the cyanobacterial host organisms comprise Synechococcus sp. PCC 7002 strains and Synechocystis sp. PCC 6803 strains.
A variety of suitable inducible promoters and promoter combinations are devised within the invention. Certain aspects and preferred embodiments of the invention require orthogonally inducible promoters in order to allow for the separate, sequential induction of the expression of the corresponding promoter-controlled first and/or second production genes by means of a change in the cultivation conditions. In some embodiments, rather than being orthogonally inducible, the different inducible promoters are inducible by the same inductor, but require inductor concentrations which are so different that the different promoters can be separately induced. Preferably, the induction conditions for different inducible promoters are so different from each other that a cross-induction is minimized or ideally eliminated. For instance, a first and second promoter that are separately inducible under different conditions means that whilst the first promoter is induced, the second promoter is maintained in an uninduced state, i.e. only less than or equal to 20%, preferably less than or equal to 15%, more preferably less than or equal to 10%, most preferred less than or equal to 5% of the first chemical compound per OD750nm of the cyanobacteria are produced via the corresponding uninduced gene compared to the induced state of the second promoter. The inventors discovered that with such a tight control of the expression of production genes which direct the metabolic flux away from the wild type cyanobacterial metabolism the genetic stability of the cyanobacterial hybrid strain can be greatly enhanced, thus enabling particularly long-termed production of the first chemical compound. The first and second promoters and/or further promoters can be inducible using different inductors such as different metal ions, different external stimuli such as heat, cold or light. In preferred embodiments, the inducible promoters are induced under conditions selected from a group comprising: by nutrient starvation, by stationary growth phase, by heat shock, by cold shock, by oxidative stress, by salt stress, by light, by darkness, by metal ions, by organic chemical compounds, and combinations thereof. For example, a particularly tight control of the expression of the first production genes can be achieved if these genes are under the transcriptional control of a Zn, Ni, or Co inducible promoter. In some preferred examples, the Co and Ni inducible promoters can be used for the transcriptional control of the first production genes if the cultivation of the cyanobacteria is done in mBG11 medium.
According to a further embodiment of the invention, the metabolically enhanced cyanobacteria can further comprise at least one recombinant regulator gene that is co-transformed with the corresponding inducible promoter, encoding a transcription factor such as a repressor or an activator binding to the inducible promoter in the case that the respective inducible promoter is heterologous to the metabolically enhanced cyanobacterium. For example, if a regulator gene codes for a repressor protein binding to the respective promoter in its uninduced state and said promoter is recombinantly introduced into a cyanobacterium as heterologous gene without the respective regulator gene, the promoter would be a constitutive promoter. Likewise, in the case that the recombinant regulator gene is an activator protein which binds to the respective promoter in the induced state and promotes binding of RNA polymerase to initiate transcription, these promoters would not be functional without the activator protein when they are heterologous to the metabolically enhanced cyanobacterium.
In certain preferred embodiments, the inducible promoters are selected from a group comprising: PntcA, PnblA, PisiA, PpetJ, PpetE, PggpS, PpsbA2, PpsaA, PsigB, PlrtA, PhtpG, PnirA, PnarB, PnrtA, PhspA, PclpB1, PhliB, PcrhC, PziaA, PsmtA, PcorT, PnrsB, PnrsB916, PaztA, PbmtA, Pbxa1, PzntA, PczrB, PnmtA. In certain other preferred embodiments, truncated or partially truncated versions of these promoters including only a small portion of the native promoters upstream of the transcription start point, such as the region ranging from −35 to the transcription start can often be used. Furthermore, introducing nucleotide changes into the promoter sequence, e.g. into the TATA box, the operator sequence, 5′-untranslated region and/or the ribosomal binding site (RBS) can be used to tailor or optimise the promoter strength and/or its induction conditions, e.g. the concentration of inductor required for induction. In some preferred variants, the different inducible promoters are inducible by different metal ions. For example, the first promoter for a first and/or second production gene can be the PpetE or PpetJ promoter, such that the induction occurs under copper-addition or copper-depletion. The second promoter for the first and/or second production gene can then be the Zn2+-inducible promoter PziaA, PsmtA or PaztA. A further third promoter for the first and/or second production gene can be the Co2+-inducible promoter PcorT. A further fourth promoter for the first and/or second production gene can be the Ni2+-inducible promoter PnrsB.
In certain embodiments, the second production gene encodes a biocatalyst that does not affect the metabolic carbon flow of the cyanobacterial cell by its expression and therefore has no influence on the metabolic competition between cell growth and production of the chemical compound. Accordingly, genetic alterations in this gene do not provide a selection advantage and do not lead to overgrowing of the culture by corresponding revertants. For this reason, in some preferred embodiments, such second production genes can be put under the control of promoters different from the inducible promoters, for example constitutive promoters such as the Prbc promoter or an improved variant thereof. This promoter controls the transcription of the genes encoding the ribulose biphosphate carboxylase/oxygenase (rbcLXS genes: slr0009, slr0011 and slr0012), which is a constitutive and strong promoter. Similarly, also a third or further production gene encoding biocatalysts such as enzymes which catalyze metabolic reactions that do not affect the metabolic carbon flow of the cyanobacterial cell by their expression can be put under the control of a constitutive promoter. In some further examples, said second or further production gene can for instance encode a biocatalyst which catalyzes metabolic reactions already present in the wild type cyanobacterium.
Some preferred examples of metabolically enhanced cyanobacteria comprise a first production gene which is under the transcriptional control of the Zn-inducible promoter PziaA or the Zn-inducible promoter PsmtA, a second first production gene under the transcriptional control of the nickel-inducible promoter PnrsB and a third first production gene under the transcriptional control of the cobalt-inducible promoter PcorT, whereas the second production gene is under the transcriptional control of the constitutive Prbc promoter or an improved veriant thereof.
In other preferred examples, the metabolically enhanced cyanobacterium can comprise two or more first production genes under the transcriptional control of a first, second or further promoter, wherein the promoters are inducible by the same inductor, but wherein the concentration of inductor required for induction of the first promoter is different from the concentration of inductor required for induction of the second or further promoter, and the concentration of inductor required for induction of the second promoter is different from the concentration of inductor required for the further promoter. In typical examples, the concentration of inductor required for the induction of the first promoter is lower compared to the concentration of inductor required for induction of the second promoter, and the concentration of inductor required for the induction of the second promoter is lower compared to the concentration of inductor required for induction of the third promoter. In some other examples, wherein the promoter responds to a depletion of the corresponding inductor, the concentration of inductor required for the induction of the first promoter is higher compared to the concentration of inductor required for induction of the second promoter and the concentration of inductor required for the induction of the second promoter is higher compared to the concentration of inductor required for induction of the third promoter. According criteria can be applied to a fourth or further promoter. For instance, the first, second and a further third promoter are all Zn-inducible promoters, but the first promoter requires a concentration of 1-5 μM Zn2+ for induction, the second promoter requires a concentration of 5-10 μM Zn2+ for induction, and the third promoter requires a concentration of >10 μM Zn2+ for induction, such that these promoters can be used inventively using distinct concentrations of the same inductor for sequential induction of the first production genes. Suitable different promoters which require different concentrations of inductor could be for instance the Zn-inducible promoters PziaA, PsmtA and PaztA. Alternatively, modified variants of the same promoter could be used, for instance recombinantly modified versions of the Zn-inducible PziaA promoter, which have been tailored to respond to different concentrations of the inductor.
The first chemical compound according to the present invention can be selected for example from the group of alcohols, alkanes, polyhydroxyalkanoates, e.g. PHB, fatty acids, fatty acid esters, carboxylic acids, such as amino acids, terpenes and terpenoids, peptides, polyketides, hydrogen, alkaloids, lactams, such as pyrrolidone, alkenes and ethers, such as THF and combinations thereof. In a preferred variant the first chemical compound comprises a biofuel. In a further variant of the genetically enhanced cyanobacteria provided by the invention, the first chemical compound comprises a hydrocarbon-based biofuel which is selected from the group comprising ethanol, isobutanol, fatty acid esters, alkanols, alkenes and alkanes. In another preferred variant, the first chemical compound comprises ethanol. The first chemical compound can also comprise ethylene or isoprene.
Depending on the first valuable chemical compound to be produced, the respective first production genes encoding enzymes for the production of these first chemical compounds have to be introduced into the cyanobacteria. For example, if the first chemical compound is ethanol, the first production gene encoding enzymes for ethanol production can be Pdc enzymes catalyzing the reaction from pyruvate to acetaldehyde or an AdhE enzyme which directly converts acetyl coenzyme A to ethanol. The second production gene can for instance be an Adh enzyme catalyzing the conversion of acetaldehyde to the first chemical compound ethanol.
Two other alcohols which are relatively widespread are propanol and butanol. Similar to ethanol, they can be produced by fermentation processes. The following enzymes are involved in isopropanol fermentation and can be encoded first and/or second production genes according to the present invention: acetyl-CoA acetyltransferase (EC:2.3.1.9), acetyl-CoA: acetoacetyl-CoA transferase (EC:2.8.3.8), acetoacetate decarboxylase (EC:4.1.1.4) and isopropanol dehydrogenase (EC:1.1.1.80).
The following enzymes are involved in isobutanol fermentation and can constitute first and/or second production genes according to the present invention: acetolactate synthase (EC:2.2.1.6), acetolactate reductoisomerase (EC:1.1.1.86), 2,3-dihydroxy-3-methylbutanoate dehydratase (EC:4.2.1.9), □-ketoisovalerate decarboxylase (EC:4.1.1.74), and alcohol dehydrogenase (EC:1.1.1.1).
In the case that ethylene is to be produced as a first chemical compound, the first production gene encodes an enzyme for ethylene formation, in particular the ethylene-forming enzyme 1-aminocyclopropane-1-carboxylate oxidase (EC 1.14.17.4), which catalyzes the last step of ethylene formation, the oxidation of 1-aminocyclopropane-1-carboxylic acid to ethylene. The substrate for the ethylene-forming enzyme is synthesized by the enzyme 1-aminocyclopropane-1-carboxylic acid synthase (EC 4.4.1.14) from the amino acid methionine.
If the first chemical compound is an isoprenoid such as isoprene, the first production gene encodes an enzyme such as isoprene synthase. Isoprene synthase (EC 4.2.3.27) catalyzes the chemical reaction from dimethylallyl diphosphate to isoprene and diphosphate.
Terpenes are a large and very diverse class of organic compounds, produced primarily by a wide variety of plants, particularly conifers. Terpenes are derived biosynthetically from units of isoprene and are major biosynthetic building blocks in nearly every living organism. For example, steroids are derivatives of the triterpene squalene. When terpenes are chemically modified, for instance by oxidation or rearrangement of the carbon skeleton, the resulting compounds are generally referred to as terpenoids. Terpenes and terpenoids are the primary constituents of the essential oils for many types of plants and flowers. Examples of biosynthetic enzymes are farnesyl pyrophosphate synthase (EC 2.5.1.1), which catalyzes the reaction of dimethylallylpyrophosphate and isopentenyl pryrophosphate yielding farnesyl pyrophosphate. Another example is geranylgeranyl pyrophosphate synthase (EC 2.5.1.29), which catalyzes the reaction between transfarnesyl diphosphate and isopentenyl diphosphate yielding diphosphate and geranylgeranyl diphosphate.
In the case that the first chemical compound is hydrogen, the first production genes can for example code for hydrogenase, an enzyme catalyzing the following reaction:

12H++12Xreduced→6H2+12X+oxidized,

wherein X is an electron carrier such as ferredoxin.

Another example of first chemical compounds are the so-called non-ribosomal peptides (NRP) and the polyketides (PK). These compounds are synthesized by plants, fungi and only a few bacteria such as actinomycetes, myxobacteria and cyanobacteria. They are a group of structurally diverse secondary metabolites and often possess bioactivities of high pharmacological relevance. Hybrids of non-ribosomal peptides and polyketides also exist, exhibiting both a peptide and a polyketide part. First production genes for the production of non-ribosomal peptides as the first chemical compounds are for example gene clusters encoding for non-ribosomal peptide synthetases (NRPS). NRPS are characteristic modular multidomain enzyme complexes encoded by modular non-ribosomal peptide synthetases gene clusters. Examples for non-ribosomal peptide synthetases are actinomycin synthetase and gramicidin synthetase.
In general there are two distinct groups of polyketides (PK), the reduced polyketides of type I, the so-called macrolides and the aromatic polyketides of type II. Type I polyketides are synthesized by modular polyketide synthases (PKS), which are characteristic modular multidomain enzyme complexes encoded by modular PKS gene clusters. Examples for first production genes for the production of type I polyketides are the rapamycin synthase gene cluster and the oleandomycin synthase gene cluster. One example for a first production gene for type II polyketides is the actinorhodin polyketide synthase gene cluster.
Examples for first production genes for the production of hybrids of polyketides and non-ribosomal peptides are the microcystin synthetase gene cluster, microginin synthetase gene cluster, myxothiazole synthetase gene cluster.
Further examples of first chemical compounds are alkaloids. Alkaloids are a compound group which is synthesized by plants. Alkaloids have highly complex chemical structures and pronounced pharmacological activities. An example for biosynthetic enzymes for alkaloids which can be encoded by first production genes for the production of the chemical compound according to the present invention is strictosidine synthase, which catalyzes the stereoselective Pictet-Spengler reaction of tryptamine and secologanin to form 3a(S)-strictosidine. The primary importance of strictosidine is not only its precursor role for the biosynthetic pathway of ajmaline but also because it initiates all pathways leading to the entire monoterpene indol alkaloid family. Another example of an enzyme encoded by a first production gene is strictosidine glucosidase from the ajmaline biosynthetic pathway. This enzyme is able to activate strictosidine by deglycosylation thus generating an aglycon. This aglycon of strictosidine is the precursor for more than 2,000 monoterpenoid indol alkaloids.
Further examples of enzymes encoded by first production genes are:

    
    
        (R,S)-3′-hydroxy-N-methylcoclaurine 4′-O-methyltransferase (4′OMT) central to the biosynthesis of most tetrahydrobenzylisoquinolin-derived alkaloids;
        Berberine bridge enzyme (BBE) specific to the sanguinarine pathway;
        (R,S)-reticuline 7-O-methyltransferase (7OMT) specific to laudanosine formation;
        Salutaridinol 7-O-acetyltransferase (SalAT) and codeinone reductase that lead to morphine.
    
    


Vitamins, as yet further examples of first chemical compounds, are organic compounds that are essential nutrients for certain organisms and act mainly as cofactors in enzymatic reactions but can also have further importance, e.g. as anti oxidants in case of vitamin C. Vitamin C can be synthesized via the L-Ascorbic acid (L-AA) biosynthetic pathway from D-glucose in plants. The following enzymes are involved in vitamin C synthesis and can be encoded by first and/or second production genes according to the present invention: Hexokinase, Glucose-6-phosphate isomerase, Mannose-6-phosphate isomerase, Phosphomannomutase, Mannose-1-phosphate guanylyltransferase, GDP-mannose-3,5-epimerase, GDP-L-galactose phosphorylase, L-Galactose 1-phosphate phosphatase, L-galactose dehydrogenase, L-galactono-1,4-lactone dehydrogenase.
Lactams, as another example of first chemical compounds, are cyclic amides wherein the prefixes indicate how many carbon atoms (apart from the carbonyl moiety) are present in the ring: β-lactam (2 carbon atoms outside the carbonyl, 4 ring atoms in total), γ-lactam (3 and 5), δ-lactam (4 and 6). One example for a γ-lactam is pyrrolidone, a colorless liquid which is used in industrial settings as a high-boiling, non-corrosive, polar solvent for a wide variety of applications. It is also an intermediate in the manufacture of polymers such as polyvinylpyrrolidone and polypyrrolidone.
Yet another example of first chemical compounds according to the present invention are ethers, a class of organic compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups—of general formula R—O—R. A well-known example is tetrahydrofuran (THF), a colorless, water-miscible organic liquid. This heterocyclic compound is one of the most polar ethers with a wide liquid range, it is a useful solvent. Its main use, however, is as a precursor to polymers.
One example for the natural occurring ethers are the divinyl ether oxylipins. The main enzymes involved in their biosynthesis are the lipoxygenase and especially the divinyl ether synthase.
Alkanes, also known as saturated hydrocarbons, are chemical compounds that consist only of the elements carbon and hydrogen (i.e., hydrocarbons), wherein these atoms are linked together exclusively by single bonds (i.e., they are saturated compounds). Each carbon atom must have 4 bonds (either C—H or C—C bonds), and each hydrogen atom must be joined to a carbon atom (H—C bonds). The simplest possible alkane is methane, CH4. There is no limit to the number of carbon atoms that can be linked together. Alkanes, observed throughout nature, are produced directly from fatty acid metabolites. A two-gene pathway widespread in cyanobacteria is responsible for alkane biosynthesis and can be included in the first and/or second production genes. An acyl-ACP reductase (EC: 1.3.1.9) converts a fatty acyl-ACP into a fatty aldehyde that is subsequently converted into an alkane/alkene by an aldehyde decarbonylase (EC:4.1.99.5.).
Further examples of the first chemical compound include biopolymers such as polyhydroxyalkanoates or PHAs which are linear polyesters produced in nature by bacterial fermentation of sugar or lipids. They are produced by the bacteria to store carbon and energy. The simplest and most commonly occurring form of PHA is the fermentative production of poly-3-hydroxybutyrate (P3HB), but many other polymers of this class are produced by a variety of organisms: these include poly-4-hydroxybutyrate (P4HB), polyhydroxyvalerate (PHV), polyhydroxyhexanoate (PHH), polyhydroxyoctanoate (PHO) and their copolymers. The main enzymes involved in PHA synthesis are as follows: For P3HB synthesis two molecules of acetyl-CoA were condensed by a β-ketothiolase (EC:2.3.1.9) to synthesize acetoacetyl-CoA, which is converted to (R)-3-hydroxybutyryl-CoA (3HBCoA) by NADPH-dependent acetoacetyl-CoA reductase (EC:1.1.1.36). The 3HBCoA is subsequently polymerized by poly(3-hydroxyalkanoate) synthase (EC:2.3.1.-) and converted to (P3HB). These can be included in the first and/or second production genes according to the present invention.
About 100,000 metric tons of the natural fatty acids are consumed in the preparation of various fatty acid esters. The simple esters with lower chain alcohols (methyl-, ethyl-, n-propyl-, isopropyl-, and butyl esters) are used as emollients in cosmetics and other personal care products and as lubricants. Esters of fatty acids with more complex alcohols, such as sorbitol, ethylene glycol, diethylene glycol and polyethylene glycol are consumed in foods, personal care, paper, water treatment, metal working fluids, rolling oils and synthetic lubricants. Fatty acids are typically present in the raw materials used for the production of biodiesel. A fatty acid ester (FAE) can be created by a transesterification reaction between fats or fatty acids and alcohols. The molecules in biodiesel are primarily fatty acid methyl esters FAMEs, usually obtained from vegetable oils by transesterification with methanol. The esterification of the ethanol with the acyl moieties of coenzyme A thioesters of fatty acids can be realized enzymatically by an unspecific long-chain-alcohol 0-fatty-acyltransferase (EC 2.3.1.75) from Acinetobacter baylyi strain ADP1.
In preferred embodiments, the metabolically enhanced cyanobacteria allow for a long-term production of the first chemical compound of at least or more than 60 days.
Metabolically enhanced cyanobacteria according to some other embodiments of the present invention can also include another production pathway for a second chemical compound so that these cyanobacteria produce the first and the second chemical compound. The second chemical compound differs from the first chemical compound and can also be selected from the above mentioned chemicals
The second aspect of the present invention is directed to a method for producing metabolically enhanced cyanobacteria according to the first aspect of the invention, comprising the following method steps:

    
    
        a) Providing the following at least two transformable nucleic acid sequences:
        
            said first production gene under the transcriptional control of said first promoter for the first production gene;
            said first production gene under the transcriptional control of said second promoter for the first production gene;
        
        
        b) Transforming said at least two transformable nucleic acid sequences into the cyanobacteria cells.
    
    


In some embodiments, the at least two transformable nucleic acid sequences are provided on one genetic construct which is transformed into the cyanobacterial cell. In other embodiments, the at least two transformable nucleic acid sequences are provided on different genetic constructs which are separately transformed into the cyanobacterial cell. In yet other embodiments, a third or further transformable nucleic acid sequence is provided, either on one genetic construct with at least one of said at least two transformable nucleic acid sequences, or as one or more separate genetic constructs, and is transformed into the cyanobacterial cell.
The laboratory procedures in cell culture, molecular cloning and nucleic acid chemistry which are required to provide a transformable nucleic acid sequence according to method step a) are those well-known and commonly employed in the art. The techniques and procedures are generally performed according to conventional methods in the art and various general references, see, for example: Molecular Cloning: A Laboratory Manual (Third Edition), Sambrook, J., et al. (2001) Cold Spring Harbor Laboratory Press; Current Protocols in Microbiology (2007) Edited by Coico, R, et al., John Wiley and Sons, Inc.; The Molecular Biology of Cyanobacteria (1994) Donald Bryant (Ed.), Springer Netherlands; which are hereby incorporated in their entirety.
A transformable nucleic acid sequence as used herein means a nucleotide sequence (DNA sequence) capable of directing expression of a particular nucleotide sequence in the cyanobacterial host cell. Nucleic acid sequences of interest can, for instance, be obtained from the GenBank database or derived from protein databases. The sequence information may, for instance, be used to amplify the nucleic acid sequence of interest from a host organism using the polymerase chain reaction (PCR) technique. Suitable primer pairs for the PCR can be designed on the basis of the available sequence information using design algorithms or design rules which are known to those skilled in the art. The design of the primers can also accommodate non-coding flanking sequences which can facilitate the cloning and expression of the nucleic acid sequence. For example, restriction endonuclease recognition sites can be incorporated into the primers to enable the specific ligation of the nucleic acid sequence into a cloning and/or expression vector. In addition, the design can incorporate nucleic acid sequences which facilitate the insertion of the genetic construct into genetic elements via homologous recombination. Alternatively, the nucleic acid sequences can be synthetically produced. In providing the nucleic acid sequence for transformation, additional features can be considered, for instance incorporating an optimized codon-usage for cyanobacteria, introducing conservative mutations, elimination of restriction sites, or incorporating degenerated nucleic acid sequences. The nucleic acid sequence may further be inserted into a suitable cloning or expression vehicle to provide the transformable genetic construct of method step a). To this end, the restriction sites incorporated into the design of the nucleic acid sequence are preferably designed to match appropriate restriction sites of the vehicle of choice. Alternatively, the nucleic acid sequences can for example also be inserted into vehicles by recombination, if their design incorporates a suitable recombination site and the vehicle of choice contains a cognate recombination site as well. Vehicles of choice may, for instance, be vectors suitable for amplification and/or expression in cyanobacterial cells. Such vectors may also be used to facilitate further cloning steps, shuttling between vector systems, expression of the inserted product in cyanobacterial host cells, or integration of the inserted product into the genome of the cyanobacterial host cell.
Numerous methods can be used to transform the transformable nucleic acid sequence into the cyanobacterial cells in method step b). For instance, the insertion of the genetic construct into the host cell can be accomplished by methods of direct uptake, conjugation or electroporation. According to the present invention, transforming the cyanobacteria cells means that the genetic construct may be maintained as a non-integrated, self-replicating vector, for example a plasmid, or alternatively may be integrated into the host cell genome, for instance an endogenous plasmid or a bacterial chromosome. Transformation by direct uptake is possible for several cyanobacterial species that are naturally competent, i.e. capable of transporting DNA across the cell membrane. For instance, Synechocystis sp. PCC6803, Synechococcus elongatus PCC 7942, Synechococcus sp. PCC 7002 and Thermosynechococcus elongatus BP-1 are naturally transformable. Alternatively, transformation of cyanobacterial cells can be accomplished by conjugation. For instance, transformation by conjugation has been successfully for Anabaena sp. PCC 7120, Anabaena variabilis ATCC 29413, Nostoc punctiforme ATCC 290133, Nostoc sp. PCC 7422, Synecococcus sp. MA19, Synechococcus sp. NKBG15041c, Synechococcus leopoliensis UTCC 100 and Synechocystis sp. PCC 6803. Cyanobacterial transformation has also been accomplished by electroporation, for instance of Synechocystis sp. PCC 6803. For laboratory references for these types of methodologies see, for example, A. M. Ruffing, Bioengineered Bugs 2011, 2, 136-149, and references cited therein, which are hereby incorporated in their entirety.
A selection marker is required to screen for successful transformation events. In a preferred embodiment, the transformable genetic construct therefore further comprises an individual selection marker which allows selection of positive transformants carrying said transformable genetic construct. In addition, since according to the present invention the cyanobacterial cells can comprise different transformed genetic constructs located on the same as well as different genetic elements, these transformable genetic constructs have to carry different selective markers to accordingly select positive transformation events with each genetic construct and each genetic element. In a preferred embodiment, the transformable genetic construct further comprises a ubiquitous selection marker, i.e. a selection marker which is common to all the different transformable genetic constructs transformed into the cyanobacterium. The ubiquitous selection marker allows for selection of positive transformants carrying any of said transformable genetic constructs. In a preferred embodiment, the method comprises the use of selection markers that are based on antibiotic resistance, selection markers independent of antibiotic resistance, as well as combinations thereof. A variety of antibiotic resistance cassettes can be used as selective markers with cyanobacteria, for instance ABR cassettes for ampicillin, kanamycin, neomycin, gentamycin, streptomycin, spectinomycin, chloramphenicol, erythromycin, zeozin. Antibiotic resistance-free systems comprise, for example, selection markers that confer prototrophy to an auxotrophic cyanobacterial strain, or confer resistance against certain heavy metal ions as cobalt or zinc.
In a third aspect of the present invention, the invention provides a method for producing a first chemical compound using a metabolically enhanced cyanobacterium comprising the method steps of:

    
    
        A) Culturing the metabolically enhanced cyanobacterium under conditions for induction of the first promoter for the first production gene, the cyanobacterium producing the first chemical compound;
        B) Culturing the metabolically enhanced cyanobacterium under conditions for induction of the second promoter for the first production gene, the cyanobacterium producing the first chemical compound;
        
            wherein method step A) and method step B) are temporally separated;
            wherein the second promoter for the first production gene of method step B) is maintained in an uninduced state during method step A).
        
        
    
    


Suitable growth media for cyanobacteria comprise, for instance, the BG11 medium, which can be prepared with fresh water (BG11), sea water (mBG11) or brackish water.
The recipe for the cyanobacterial growth medium mBG11 is as follows:

    
    
        NaNO3: 1.5 g
        K2HPO4: 0.04 g
        MgSO4.7H2O: 0.075 g
        CaCl2.2H2O: 0.036 g
        Citric acid: 0.006 g
        Ferric ammonium citrate: 0.006 g
        EDTA (disodium salt): 0.001 g
        NaCO3: 0.02 g
        Trace metal mix A5: 1.0 ml
        Distilled water: 1.0 L
        (pH 7.1 adjusted after sterilization)
    
    


Herein, the recipe for the trace metal mix A5 is:

    
    
        H3BO3: 2.86 g
        MnCl2.4H2O: 1.81 g
        *ZnSO4.7H2O: 0.222 g
        NaMoO4.2H2O: 0.39 g
        CuSO4.5H2O: 0.079 g
        *Co(NO3)2.6H2O: 49.4 mg
        Distilled water or seawater (35 practical salinity units=psu; see Unesco (1981a). The Practical Salinity Scale 1978 and the International Equation of State of Seawater 1980. Tech. Pap. Mar. Sci., 36: 25 pp.): 1.0 L
        The asterisk (*) denotes those metal supplements that can be either omitted or used in reduced amounts if these metals are also used as inductor for corresponding metal-inducible promoters in the metabolically enhanced cyanobacterial strain.
    
    


Due to the first production genes being under the control of inducible promoters, the cyanobacteria can be grown to a high density prior to method step A) in the uninduced state, since the flux of fixed-carbon is not diverted from the cells' natural metabolism, i.e. cell growth. According to the present invention, the conditions for induction of the first promoter for the first production gene in method step A) can be, for instance, the depletion of copper, copper addition, the addition of Zn2+, Co2+ or Ni2+ to the culture medium, iron starvation, nitrogen starvation, selected nitrogen sources in the medium, or any other suitable induction condition. In method step A), the cyanobacteria can for example be induced by adding at least 2 μM Zn2+, Co2+ or Ni2+ to the growth medium. The concentration of the inducing agent in the growth medium for an induction of the promoters can be for instance between 5 μM and 20 μM. The high cell density of the cyanobacterial culture together with the strength of the inducible promoter allows for a high production rate of the first chemical compound during method step A). If for example a drop in the production rate of the first chemical compound during method step A) is registered, method step B) is initiated by a change in the cultivation conditions, so that the second promoter for the first production gene is induced. Typically, induction of method step B) leads to a recovery of the production of the first chemical compound.
According to the teaching of the present invention, a fundamental feature of the method is that the method step A) and method step B) are temporally separated. This means that the method steps are sequentially initiated during the method for producing the first chemical compound by a change of cultivation conditions for selective induction of the first and second promoter for the first production gene. In this sense, method step B) is initiated after method step A). However, it is possible that during method step B) the conditions for induction of the first promoter for the first production gene of method step A) are maintained. For instance, if a Zn2+ salt was added for induction of the first promoter for the first production gene in method step A), it is not required that this Zn2+ salt is removed from the cultivation medium in method step B). The temporal separation of method steps A) and B) only requires that the second promoter for the first production gene of method step B) is maintained in an uninduced state during method step A). The inventors found that under these conditions the likelihood of reverted non-producing cells that can enrich and finally overgrow non-reverted producing cells is reduced, thereby enabling the long-term production of the first chemical compound according to the principle of the invention by a temporarily separated sequential induction of production genes encoding biocatalysts catalyzing the same reaction for the production of the first chemical compound.
In a preferred embodiment, the method comprises at least one further method step C) of culturing the metabolically enhanced cyanobacterium under conditions for induction of at least one further third promoter for the first production gene, the cyanobacterium producing the first chemical compound; wherein method step A), method step B) and method step C) are temporally separated from each other; wherein the third promoter for the first production gene of method step C) is maintained in an uninduced state during method steps A) and B). It is evident to those skilled in the art that the method provided by the invention can also comprise additional method steps which can be easily derived following the same principles as detailed for method steps A), B) and C).
In certain preferred embodiments, method steps A), B) and—if present—C) and further method steps comprise the expression of the at least one second production gene encoding the second biocatalyst for the production of the first chemical compound. The expression of the at least one second production gene in the respective method step can be controlled by an inducible promoter or can be constitutive. In preferred embodiments, the method steps comprise the constitutive expression of the at least one second production gene. For example, the inventors discovered that if the second biocatalyst catalyzes a reaction that does not affect the metabolic carbon flow of the cyanobacterial cell and therefore has no influence on the metabolic competition between cell growth and production of the chemical compound, the genetic pressure on the second production encoding the second biocatalyst is significantly lower compared to the genetic pressure on the first production gene encoding a biocatalyst that separates the carbon flux from the cell growth and biomass accumulation, respectively. Accordingly, genetic alterations in this gene do not provide a selection advantage and do not lead to overgrowing of the culture by corresponding revertants. According to this preferred embodiment, the second production gene can for instance encode an alcohol dehydrogenase, whereas the first production genes encode a pyruvate decarboxylase enzyme, in the case the first chemical compound is ethanol.
In certain embodiments, wherein the at least one second production gene is under the transcriptional control of the first, second or further promoter for the second production gene, also the first promoter for the second production gene is induced in method step A). In a related preferred embodiment, also the second promoter for the second production gene is induced in method step B). In yet another preferred embodiment, at least a further third promoter for the second production gene is induced in at least one further method step C). Herein, the second promoter for the second production gene of method step B) is maintained in an uninduced state during method step A), and the third promoter for the second production gene of method step C) is maintained in an uninduced state during method steps A) and B).
The simultaneous induction of the first, second and—if present—third or further promoters for the first and second production gene can be realized in different ways. For instance, the first, second and, if present, third promoter or further promoter for the first and second production gene, are either the same promoters or are promoters which are inducible under the same conditions. For instance, the first promoter for the first production gene is the zinc-inducible promoter PziaA, whereas the first promoter for the second production gene is the zinc-inducible promoter PsmtA, and the cultivation conditions in method step A) comprise a zinc concentration which is sufficient to induce both the first promoter for the first production gene and the first promoter for the second production gene. In yet another preferred embodiment, the promoters for the first and second production gene are the same promoters, for instance the first promoter for the first production gene and the first promoter for the second production gene are both the zinc-inducible promoter PziaA or the zinc-inducible promoter PsmtA. In certain preferred embodiments, both the first production genes and the second production genes of method step A) and/or method step B) and/or method step C) are transcriptionally controlled by the same single promoter. According to this embodiment, the first production gene and second production gene of the respective method step are operably linked and under the control of the same single promoter to form a functional operon. For example, a first production gene and a second production gene of a particular method step are operably linked in an operon and are co-ordinately expressed by induction of a single promoter which could be, for instance, a zinc-inducible promoter PziaA.
In a preferred embodiment of the method the metabolically enhanced cyanobacteria are subjected to sunlight and CO2 during method steps A), B) and, if present, during method step C) and further method steps. Cyanobacteria are photoautotrophic prokaryotes that perform oxygen photosynthesis. The cyanobacteria interconnect atmospheric levels of carbon dioxide through photosynthesis according to the following generic equation:

CO2+H2O→(CH2O)n+O2.

Herein, (CH2O)n represents organic matter with fixed carbon that is fed into the metabolic pathways of the cyanobacteria and can subsequently be also converted into the first chemical compound.
In a preferred embodiment of the method, culture monitoring is applied during the method steps. For example, the culturing conditions of method step A) are maintained for a period of time and/or until monitoring indicates a threshold productivity decrease of the first chemical compound, before the next method step B) is initiated. In another preferred embodiment, the culturing conditions of method step B) are maintained for a period of time and/or until monitoring indicates a threshold productivity decrease of the first chemical compound, before the next method step C) is initiated. Furthermore, it is evident to those skilled in the art that the same procedural method can be applied to further additional method steps according to the same rules specified above. In a preferred embodiment, the monitoring of the cyanobacterial culture is selected from at least one method of the group comprising: biocatalyst activity tests, determining of the concentration of the first chemical compound in the growth medium and/or in the space above the growth medium, gene expression analysis on mRNA and/or protein level, detection of mutations e.g. by enzymatic mismatch detection using a mismatch-specific DNA endonuclease (CEL-I) from celery rods as described by Qiu et al. (Qiu P, Shandilya H, D'Alessio J M, O'Connor K, Durocher J, Gerard G F.: Mutation detection using Surveyor nuclease, Biotechniques 36 (2004), 702-7), or by real-time PCR in combination with melting curve analysis and/or by sequencing, and combinations thereof. For example, biocatalysts activity tests comprise testing the enzymatic activity of the pyruvate decarboxylase enzyme when the first chemical compound is ethanol. Alternatively, the concentration of ethanol can be determined in the growth medium or in the space above the growth medium using gas chromatography. Furthermore, real-time PCR assays have proven to be a powerful tool for rapid monitoring of the genetic condition of cyanobacterial hybrid strains. For instance, amplification of a core sequence within the production gene in question, followed by melt curve analysis of the amplificates can provide qualitative information about the genetic integrity of the production genes. Suitable real-time PCR routines can be devised by those skilled in the art. For additional laboratory references, see, for example, Real-Time PCR in Microbiology: From Diagnosis to Characterization, by Ian M. Mackay (ed.), Caister Academic Press 2007.
A threshold productivity decrease according to the present invention can for example be indicated by stagnation of the content of the first chemical compound during cultivation; i.e. even though the culture might be still growing, the total concentration of the first chemical compound (e g ethanol) in the culture does not increase anymore. Alternatively, if for instance the content of the first chemical compound for three subsequent days increases 0.05% (v/v) or less, 0.03% (v/v) or less, 0.01% (v/v) or less compared to the content of the previous day, a threshold productivity decrease has set in. These values are exemplary only, because they can vary depending on the produced chemical compound, the bioreactor design and culture conditions, the scale and the cell density. A threshold productivity decrease according to the present invention can also be defined by decrease of the content of the first chemical compound during cultivation. A threshold productivity decrease as determined by biocatalyst activity tests can for example be constituted by a decrease in PDC activity of at least or under 0.5 μmol min−1 mg−1 protein, at least or under 0.4 μmol min−1 mg−1 protein, at least or under 0.3 μmol min−1 mg−1 protein or at least or under 0.2 μmol min−1 mg−1 protein. In the case that nucleic acid mismatches are determined as the means of culture monitoring, the next method step is initiated if for instance if at least or more than 10%, at least or more than 20%, or at least or more than 40% of the cyanobacterial population are reverted.
In a preferred embodiment of the method, the cyanobacterium is selected from a group comprising Synechocystis, Synechococcus, Anabaena, Chroococcidiopsis, Chlorogloeopsis, Cyanothece, Lyngbya, Phormidium, Nostoc, Spirulina, Arthrospira, Trichodesmium, Leptolyngbya, Plectonema, Myxosarcina, Pleurocapsa, Oscillatoria, Pseudanabaena. Cyanobacterium, Geitlerinema, Euhalothece, Calothrix. In more preferred embodiments, the cyanobacterial host organisms comprise Synechococcus sp. PCC 7002 and other Synechococcus strains, Synechocystis sp. PCC 6803 and other Synechocystis strains, Chlorogloeopsis strains, Chroococcidiopsis strains, and Cyanobacterium strains. In particularly preferred embodiments, the cyanobacterial host organisms comprise Synechococcus sp. PCC 7002 strains and Synechocystis sp. PCC 6803 strains.
In a fourth aspect of the invention, the invention provides a metabolically enhanced cyanobacterium for the production of a first chemical compound, comprising:

    
    
        at least a first and second first production gene encoding first biocatalysts for the production of the first chemical compound;
        wherein both first production genes are under the transcriptional control of the same inducible promoter for the first production genes;
        wherein the inducible promoter for the first production genes is gradually inducible in a dose-dependent manner;
        wherein said first biocatalysts catalyze the same chemical reaction.
    
    


According to this aspect of the invention, the use of the same inducible promoter for the first production genes allows for the first biocatalysts under the control of said promoter to be cumulatively expressed under the same induction conditions. Moreover, since said promoter for the first production genes is gradually inducible in a dose-dependent manner, the choice of induction conditions allows modulating the expression level of the first biocatalysts in an incrementing way. For example, conditions for induction can be employed that do not induce the full activity of the promoter but still lead to a cumulative expression level of the first biocatalysts that is suitable to produce the first chemical compound. Thus, the overall expression of the first biocatalysts remains high because all corresponding first production genes are expressed and the higher gene copy number compensates for the lower induction level. Hereupon, genetic alterations can occur in the corresponding first production genes. However, the inventors found that after genetic alterations occurred in one or more copies of the first production genes, the optimal expression level can yet be assured by a subsequent higher induction of the promoter for the first production genes that then increasedly drives the remaining non-altered copies of the first production genes.
The inventors concluded that in order to overcome the problem of production decays for the first chemical compound and to prolong the synthesis of the first chemical compound, the solution is a metabolically enhanced cyanobacterial strain, which comprises two or more first production genes which are transcriptionally driven by the same promoter, and wherein this promoter allows for a stepwise induction depending on the concentration of the inductor, thereby enabling the systematic modulation of the expression level of the first biocatalysts. At the same time, increasing the dose of the first production genes in conjunction with the cumulative expression of said genes, allows compensating the shortfall of expression of the first biocatalysts even though each individual of the first production gene might not be fully induced.
For example, the metabolically enhanced cyanobacterial strain can comprise two first production genes encoding first biocatalysts for the production of the first chemical compound that are under the transcriptional control of the corresponding gradually inducible promoter for the first production genes. Upon induction of the promoter, for instance to an induction level of approximately 50% compared to the full induction, the bacterial culture commences producing the first chemical compound. Upon loss of activity of the first biocatalysts following the accumulation of alterations in a statistical proportion of the first production genes, a full induction of the promoter follows to now use the full capacity of the available first production genes, i.e. to increase the chance of transcription of those gene copies which have not accumulated inactivating alterations yet and thus maintain an optimal expression level for production of the first chemical compound. In this way, a temporal extension of the production phase of the first chemical compound can be accomplished.
In preferred embodiments of the fourth aspect of the invention, the metabolically enhanced cyanobacterium comprises at least one further first production gene under the transcriptional control of the same inducible promoter for the first production genes. In this way, the accumulated expression level of the first production genes can be maintained sufficiently high under even lower starting doses of induction of the promoter. Consequently, this allows including additional discrete induction steps to further prolong the productive phase of the bacterial culture according to the principles detailed above. For example, an induction level of approximately 33% compared to the full induction at the start of the production of the first chemical compound, followed by an induction level of approximately 66%, and finally a full induction level towards the end of the production. It will be obvious from these teachings to those skilled in the art that additional first production genes can be included according to the present invention in order to be able to further reduce the starting dose of induction and/or to be able to include additional doses of induction, i.e. to choose smaller increments between the doses of different induction steps.
In certain preferred embodiments, the same single inducible promoter controls the transcription of the first production genes. For example, the first production genes are operably linked to form an operon, which is transcriptionally controlled by a single gradually inducible promoter.
In preferred embodiments, the gradually inducible promoter is chosen from a group comprising dose-dependent metal-ion inducible promoters.
In further variants of the fourth aspect of the invention, the metabolically enhanced cyanobacterium can further comprise any metabolic enhancement according to the first aspect of the invention. Furthermore, all independent and dependent claims 1-38 of the first aspect of the invention can also be applied to the claims of the fourth aspect of the invention. For example, a cyanobacterium comprising a first set of at least two first production genes according to the fourth aspect of the invention can further comprise a second or further set of first production genes according to the first aspect of the invention, i.e. each of said first, second or further set of first production genes is under the transcriptional control of (a) different gradually inducible promoter, such that each set is separately inducible under different conditions.
In a fifth aspect of the present invention, the invention provides a method for producing a first chemical compound using a metabolically enhanced cyanobacterium comprising the method steps of:

    
    
        A1) Culturing the metabolically enhanced cyanobacterium under a first condition for induction of the promoter for the first production genes, the cyanobacterium producing the first chemical compound;
        A2) Culturing the metabolically enhanced cyanobacterium under a second condition for induction of the promoter for the first production genes, the cyanobacterium producing the first chemical compound;
        
            wherein method step A1) and method step A2) are temporally separated;
            wherein the first condition for induction results in a lower induction of the promoter for the first production genes than the second condition of induction.
        
        
    
    


According to the present invention, a first fundamental feature of the method is that in method step A1) the first production genes are simultaneously expressed, but under conditions that effect only partial induction of the promoter for the first production genes. Thus, the expression level of each of the first biocatalysts alone is lower compared to conditions for full induction of the respective first production gene, but is compensated by the cumulative expression of the first production genes, so that suitable amounts of the first biocatalysts are produced for the production of the first chemical compound. A second fundamental feature of the method is that method step A1) and method step A2) are temporally separated, meaning that the method steps are sequentially initiated during the method for producing the first chemical compound. In this sense, method step A2) is initiated after method step A1). This is realized by a change of cultivation conditions, which are characterized by an increased promoter induction in method step A2) relatively compared to the promoter induction in method step A1). For instance, for dose-dependent gradually inducible promoters, the concentration of the inductor in the culture is different in method step A2) compared to method step A1) to accomplish a higher induction level. The higher induction level of the promoter in method step A2) consequently increases the transcription level of all first production genes, therefore also increasing the expression level of functional biocatalysts. This enables to counteract the loss of part of the first production genes as a result of their genetic alteration, and therefore to extend the productive phase of a culture of metabolically enhanced cyanobacteria according to the principle of the invention by means of a temporarily separated and sequentially increased induction of the promoter controlling the first production genes.
In preferred embodiments, the method comprises at least one further method step A3) of culturing the metabolically enhanced cyanobacterium under a third condition for induction of the promoter for the first production genes, the cyanobacterium producing the first chemical compound; wherein method step A1), method step A2) and method step A3) are temporally separated from each other and wherein the second condition for induction results in a lower induction of the promoter for the first production genes than the third condition of induction. In preferred embodiments, the addition of a third or further method steps can be balanced with the number of first production genes being simultaneously induced, i.e. also involve a third or further first production gene. In this way, the starting dose of induction of the gradually inducible promoter for the first production genes in method step A1) can be further reduced because the corresponding loss of expression is compensated by the higher number of the first production genes. Correspondingly, additional levels of induction, i.e. smaller increments of induction levels between consecutive method steps can be chosen. It is evident to those skilled in the art that the method provided by the invention can also comprise additional method steps which can be easily derived following the same principles as detailed for method steps A1), A2) and A3).
In a variant of the fifth aspect of the invention, the method comprises additional method steps according to the features of the third aspect of the invention. In preferred embodiments, the method steps A1), A2) and, if present, A3) or further method steps of the fifth aspect of the invention form substeps of method step A) of the third aspect of the invention. In related preferred embodiments, the steps A1), A2) and, if present, A3) or further method steps of the fifth aspect of the invention can be used inventively as substeps B1), B2) and, if present, B3) or further substep of method step B) of the third aspect of the invention.
For instance, a first set of first production genes under the transcriptional control of a gradually inducible promoter according to the fifth aspect of the invention can be used inventively to form substeps A1) to A3) of method step A) of the third aspect of the invention. When said first set of first production genes eventually becomes unproductive, a second set of first production genes under the transcriptional control of a different gradually inducible promoter according to the fifth aspect of the invention can be used inventively to form substeps B1) to B3) of method step B) of the third aspect of the invention. For this purpose, the gradually inducible promoter of said second set of first production genes of method step B) is separately inducible under different conditions compared to the gradually inducible promoter of said first set of first production genes of method step A). This variant allows for a particularly prolonged production of the first chemical compound, and can be extended to even further method steps following the principles detailed above.
In further variants of the fifth aspect of the invention, all the examples and embodiments of the method of the third aspect of the invention can also be applied to the method of the fifth aspect of the invention. Furthermore, all independent and dependent claims of the third aspect of the invention can also be applied to the claims of the fifth aspect of the invention.
Brief Description of the Nucleotide Sequences
In the following sequence descriptions, inducible promoters are denominated as “regulator gene-promoter sequence”, as for example in “ziaR-PziaA”, wherein ziaR denotes the regulator gene and PziaA denotes the promoter sequence of the zinc inducible promoter. In gene names, the term “deg” denotes degenerated versions of the corresponding wild type genes, and the terms “deg” and “fco” denote codon-degenerated and full-codon optimised versions, respectively, of the corresponding wild type genes. The asterisk (*) in promoter names denotes promoters with optimised ribosome binding site.
SEQ ID NO:1: Construct comprising zinc-inducible promoter ziaR-PziaA from Synechocystis PCC6803 (ziaR-sll0792, ziaA-slr0798) and SalI/EcoRI restriction sites.
SEQ ID NO:2: Construct comprising cobalt-inducible promoter corR-PcorT from Synechocystis PCC6803 (corR-sll0794, corT-slr0797) and SalI/EcoRI restriction sites.
SEQ ID NO:3: Construct comprising nickel-inducible promoter nrsRS-PnrsB from Synechocystis PCC6803 (nrsS-sll0798, nrsR-sll0797, nrsB-slr0793) and SalI/EcoRI restriction sites.
SEQ ID NO:4: Construct comprising zinc-inducible promoter smtB-PsmtA from Synechococcus PCC7002 (smtB-SYNPCC7002A2564, smtA-SYNPCC7002A2563) and SalI/EcoRI restriction sites.
SEQ ID NO:5: Forward primer ziaR/PziaA-SalI-fw for the amplification of the construct comprising the ziaR-PziaA promoter sequence (SEQ ID NO:1).
SEQ ID NO:6: Forward primer PziaA-SalI-fw for the amplification of the construct comprising the PziaA promoter sequence, i.e. without the ziaR regulator gene.
SEQ ID NO:7: Reverse primer PziaA-EcoRI-rev for the amplification of the construct comprising the comprising the ziaR-PziaA promoter sequence.
SEQ ID NO:8: Forward primer corR/PcorT-SalI-fw for the amplification of the construct comprising the corR-PcorT promoter sequence (SEQ ID NO:2).
SEQ ID NO:9: Reverse primer PcorT-EcoRI-rev for the amplification of the construct comprising the corR-PcorT promoter sequence.
SEQ ID NO:10: Forward primer nrsRS/PnrsB-SalI-fw for the amplification of the construct comprising the nrsRS-PnrsB promoter sequence (SEQ ID NO:3).
SEQ ID NO:11: Forward primer nrsR/PnrsB-SalI-fw for the amplification of the construct comprising the nrsR-PnrsB promoter sequence, i.e. without the nrsS regulator gene.
SEQ ID NO:12: Reverse primer PnrsB-EcoRI-rev for the amplification of the construct comprising the nrsRS-PnrsB promoter sequence.
SEQ ID NO:13: Forward primer smtB/PsmtA-SalI-fw for the amplification of the construct comprising the smtB-PsmtA promoter sequence (SEQ ID NO:4).
SEQ ID NO:14: Forward primer PsmtA-SalI-fw for the amplification of the construct comprising the PsmtA promoter sequence, i.e. without the smtB regulator gene.
SEQ ID NO:15: Reverse primer PsmtA-EcoRI-rev for the amplification of the construct comprising the smtB-PsmtA promoter sequence.
SEQ ID NO:16: Native PDC gene from Zymomonas mobilis (ZmPDC).
SEQ ID NO:17: Native PDC gene from Zymobacter palmae (ZpPDC).
SEQ ID NO:18: Codon-degenerated PDC gene from Zymomonas mobilis (ZmPDCdeg).
SEQ ID NO:19: Codon-degenerated PDC gene from Zymobacter palmae (ZpPDCdeg).
SEQ ID NO:20: Self-replicating broad host range vector pVZ322a with aph (KanR2), GmR and CmR antibiotic resistance cassettes. CmR is eliminated in ethanologenic constructs due to insertion of ethanologenic genes via SalI/SbfI into this locus.
SEQ ID NO:21: Self-replicating broad host range vector pVZ325a with Sp/Sm, GmR and CmR antibiotic resistance cassettes. CmR is eliminated in ethanologenic constructs due to insertion of ethanologenic genes via SalI/SbfI into this locus.
SEQ ID NO:22: Nucleotide sequences of ethanologenic gene cassette from plasmid #1121 pVZ322a-smtB-PsmtA-ZmPDCoop-PrbcL-synADH(deg) integrated via SalI/SbfI into pVZ322a.
SEQ ID NO:23: Nucleotide sequences of ethanologenic gene cassette from plasmid #1217 pVZ325a-corR-PcorT-ZmPDCdsrA/oop-PrbcL*-synADH(deg) integrated via SalI/SbfI into pVZ325a.
SEQ ID NO:24: Nucleotide sequences of ethanologenic gene cassette from plasmid #1227 pVZ325a-nrsR-PnrsB-ZmPDCdsrA/oop-PrbcL*-synADH(deg) integrated via SalI/SbfI into pVZ325a.
SEQ ID NO:25: Nucleotide sequences of ethanologenic gene cassette from plasmid #1356 pVZ325a-nrsRS-PnrsB*-ZpPDCdsrA/oop-PrbcL*-synADH(deg) integrated via SalI/SbfI into pVZ325a.
SEQ ID NO:26: Nucleotide sequences of ethanologenic gene cassette from plasmid #1329 pVZ325a-nrsR-PnrsB-zpPDC-corR-PcorT-zmPDC(fco) integrated into pVZ325a.
SEQ ID NO:27: Nucleotide sequences of ethanologenic gene cassette from plasmid #1375 pVZ325a-nrsRS-PnrsB-zpPDC-corR-PcorT*-zmPDCdeg integrated into pVZ325a.
SEQ ID NO:28: Nucleotide sequences of ethanologenic gene cassette from plasmid #1376 pVZ325a-nrsRS-PnrsB*-zpPDC-corR-PcorT*-zmPDCdeg integrated into pVZ325a.
SEQ ID NO:29: Nucleotide sequences of ethanologenic gene cassette from plasmid #1379 pVZ325a-nrsR-PnrsB-zpPDC-corR-PcorT-zmPDCdeg integrated into pVZ325a.
SEQ ID NO:30: Nucleotide sequence of plasmid #1145 pJET-glgA::ziaR-PziaA-ZmPDC-PrbcL-synADH(deg)-Cm used for transformation of Synechocystis PCC6803 via integration into the glgA1 gene locus in the genome.
SEQ ID NO:31: Nucleotide sequence of plasmid TK115 pGEM-AQ4::smtB-PsmtA-ZmPDC-PrbcL-synADH(deg)-Nm used for transformation of Synechococcus PCC7002 via integration into the endogenous pAQ4 plasmid.
SEQ ID NO:32: Nucleotide sequence of flanking region pAQ4-FA with NsiI/SalI restriction sites for pAQ4 integration via homologous recombination.
SEQ ID NO:33: Forward primer #323 for amplification of flanking region pAQ4-FA.
SEQ ID NO:34: Reverse primer #324 for amplification of flanking region pAQ4-FA.
SEQ ID NO:35: Nucleotide sequence of flanking region pAQ4-FB with NotI/SpeI restriction sites for pAQ4 integration via homologous recombination.
SEQ ID NO:36: Forward primer #325 for amplification of flanking region pAQ4-FB.
SEQ ID NO:37: Reverse primer #326 for amplification of flanking region pAQ4-FB.
SEQ ID NO:38: Forward primer #327 for amplification of flanking region pAQ3-FA (as published by Xu et al, 2011) with NsiI/SalI restriction sites.
SEQ ID NO:39: Reverse primer #328 for amplification of flanking region pAQ3-FA (as published by Xu et al, 2011).
SEQ ID NO:40: Forward primer #329 for amplification of flanking region pAQ3-FB (as published by Xu et al, 2011).
SEQ ID NO:41: Reverse primer #330 for amplification of flanking region pAQ3-FB (as published by Xu et al, 2011) with NotI/SpeI restriction sites.
SEQ ID NO:42: Nucleotide sequence of flanking region pAQ1-FA2 with NsiI/SalI restriction sites for pAQ1 integration via homologous recombination.
SEQ ID NO:43: Forward primer #336 for amplification of flanking region pAQ1-FA2.
SEQ ID NO:44: Reverse primer #337 for amplification of flanking region pAQ1-FA2.
SEQ ID NO:45: Nucleotide sequence of flanking region pAQ1-FB2 with NotI/SpeI restriction sites for pAQ1 integration via homologous recombination.
SEQ ID NO:46: Forward primer #338 for amplification of flanking region pAQ1-FB2.
SEQ ID NO:47: Reverse primer #339 for amplification of flanking region pAQ1-FB2.
SEQ ID NO:48: Nucleotide sequences of ethanologenic gene cassette from #1381 pVZ325a-nrsRS-PnrsB-zpPDC-corR-PcorT-zmPDCdeg integrated into pVZ325a.
SEQ ID NO:49: Nucleotide sequences of ethanologenic gene cassette from #1383 pVZ325a-nrsRS-PnrsB*-zpPDC-corR-PcorT-zmPDCdeg integrated into pVZ325a.
SEQ ID NO:50: Nucleotide sequences of ethanologenic gene construct from #1389 pJet-pSYSG::nrsRS-PnrsB-zpPDC(deg)-Gm for homologous integration into Synechocystis PCC 6803 endogenous pSYSG plasmid.
SEQ ID NO:51: Nucleotide sequences of ethanologenic gene cassette from #1391 pVZ324a-corR-PcorT-ZpPDC integrated into pVZ325a.
SEQ ID NO:52: Nucleotide sequence of plasmid TK193 pGEM-AQ3::nrsRS-PnrsB-zpPDC(deg)-Gm used for transformation of Synechococcus PCC7002 via integration into the endogenous pAQ3 plasmid.
SEQ ID NO:53: Reverse primer PcorT*-EcoRI-rev for the amplification of the construct comprising the corR-PcorT promoter sequence (SEQ ID NO:2) incorporating an optimised RBS.
SEQ ID NO:54: Reverse primer PnrsB*-EcoRI-rev for the amplification of the construct comprising the nrsRS-PnrsB promoter sequence (SEQ ID NO:3) incorporating an optimised RBS.
SEQ ID NO:55: SynADH gene (slr1192) from Synechocystis sp. PCC 6803.
SEQ ID NO:56: Codon-degenerated SynADH gene (slr1192) from Synechocystis sp. PCC 6803.
SEQ ID NO:57: Nucleotide sequences of ethanologenic gene cassette from plasmid #1356 pVZ325a-nrsRS-PnrsB*-ZpPDC-PrbcL*-synADH(deg) integrated via SalI/SbfI into pVZ325a.
SEQ ID NO:58: Full codon-optimized pdc gene from Zymomonas mobilis (ZmPDCfco).
SEQ ID NO:59: Forward primer pSYSG-P1-XbaI-fw for amplification of pSYSG-P1 (SEQ ID NO:61).
SEQ ID NO:60: Reverse primer pSYSG-P1-XmaI-rev for amplification of pSYSG-P1 (SEQ ID NO:61).
SEQ ID NO:61: Nucleotide sequence of engineered flanking region pSYSG-P1 for pSYSG integration via homologous recombination.
SEQ ID NO:62: Forward primer pSYSG-P2-XhoI-fw for amplification of pSYSG-P2 (SEQ ID NO:64).
SEQ ID NO:63: Reverse primer pSYSG-P2-NotI-fw for amplification of pSYSG-P2 (SEQ ID NO:64).
SEQ ID NO:64: Nucleotide sequence of engineered flanking region pSYSG-P2 for pSYSG integration via homologous recombination.
SEQ ID NO:65: Nucleotide sequence of plasmid TK162 pGEM-AQ3::smtB-PsmtA-zmPDC_oop-PrbcL-synADHdeg_oop used for transformation of Synechococcus sp. PCC 7002 via integration into the endogenous pAQ3 plasmid.
SEQ ID NO:66: Nucleotide sequence of plasmid #1233 pGEM-AQ4::smtB-PsmtA-zpPDC-PrbcL*-synADHdeg for transformation of Synechococcus sp. PCC 7002 via integration into the endogenous pAQ4 plasmid.
SEQ ID NO:67: Nucleotide sequence of plasmid #1374 pVZ325a-nrsR-PnrsB-zpPDC_ter-corR-PcorT*1-zmPDC\deg_spf\ter for transformation of Synechocystis sp.PCC6803.
SEQ ID NO:68: Nucleotide sequence of plasmid #1460 pVZ325a-nrsRS-PnrsB916-PDC_dsrA-Prbc*-synADHdeg for transformation of Synechococcus sp. PCC7002.
SEQ ID NO:69: Nucleotide sequence of plasmid #1470 pAQ3-corR-PcorT*1-zmPDCdeg_spf-Prbc*-synADHoop for transformation of Synechococcus sp. PCC7002 via integration into the endogenous pAQ3 plasmid.
SEQ ID NO:70: Nucleotide sequence of plasmid #1473 pAQ1::nrsRS-PnrsB193-PDC-PrbcL*-synADH_oop-Sp for transformation of Synechococcus sp. PCC7002 via integration into the endogenous pAQ1 plasmid.
SEQ ID NO:71: Nucleotide sequence of plasmid #1332 pGEM-AQ4::corR-PcorT-zpPDC*_ter-PrbcL*-synADH_oop-Nm for integration into the endogenous pAQ4 plasmid of Synechococcus sp. PCC7002.
SEQ ID NO:72: Nucleotide sequence of plasmid #1627 pVZ326a-PnrsB(ABCC916)-PDC_dsrA-Prbc*(optRBS)-synADHoop-nrsRSBAD(ABCC916) for transformation of Synechococcus sp. PCC7002.
SEQ ID NO:73: Nucleotide sequence of plasmid #1329 pVZ325a-nrsR-PnrsB-zpPDCter-corR-PcorT-zmPDC(fco)_oop for transformation of Synechocystis sp. PCC6803.
SEQ ID NO:74: Nucleotide sequence of plasmid #1379 pVZ325a-nrsR-PnrsB-zpPDCter-corR-PcorT-zmPDCdeg_spf for transformation of Synechocystis sp. PCC6803.
SEQ ID NO:75: Nucleotide sequence of plasmid #1356 pVZ325a-nrsRS-PnrsB*-zpPDCter-Prbc*-synADHdeg_oop for transformation of Synechococcus sp. PCC7002.
SEQ ID NO:76: Nucleotide sequence of plasmid #1217 pVZ325a-corR-PcorT-zmPDC_dsrA-Prbc*-synADHdeg_oop for transformation of Synechococcus sp. PCC7002.
SEQ ID NO:77: Nucleotide sequence of plasmid #1227 pVZ325a-corR-PcorT-zmPDC_dsrA-Prbc*-synADHdeg_oop for transformation of Synechocystis sp. PCC6803.
SEQ ID NO:78: Nucleotide sequence of plasmid #1480 pAQ3-aztR-PaztA-zmPDCdeg_spf-Prbc*-synADH_oop for transformation of Synechococcus sp. PCC7002 via integration into the endogenous pAQ3 plasmid.
SEQ ID NO:79: Nucleotide sequence of plasmid #1563 pGEM-gpA::smtB-PsmtA-zmPDC_dsrA-Prbc*-synADH_oop for transformation of Synechococcus sp. PCC7002 by chromosomal integration between gene loci A0124 and A0125.
SEQ ID NO:80: Nucleotide sequence of plasmid #1568 pGEM-gpB::smtB-PsmtA-zmPDCdeg_spf-Prbc*-synADH_oop for transformation of Synechococcus sp. PCC7002 by chromosomal integration between gene loci A1330 and A1331.
SEQ ID NO:81: Nucleotide sequence of plasmid #1692 pGEM-gpC::smtB-PsmtA-zmPDC_oop-PrbcL-synADHdeg_oop for transformation of Synechococcus sp. PCC7002 by chromosomal integration between gene loci A2578 and A2579.
SEQ ID NO:82: Nucleotide sequence of plasmid #1564 pGEM-gpA::corR-PcorT-zmPDC_dsrA-Prbc*synADH_oop for transformation of Synechococcus sp. PCC7002 by chromosomal integration between gene loci A0124 and A0125.
SEQ ID NO:83: Nucleotide sequence of plasmid #1633 pGEM-gpB::corR-PcorT*1-zmPDCdeg_spf-Prbc*-synADH_oop for transformation of Synechococcus sp. PCC7002 by chromosomal integration between gene loci A1330 and A1331.
SEQ ID NO:84: Nucleotide sequence of plasmid #1574 pGEM-gpC::corR-PcorT-zpPDC ter-Prbc*-synADHdeg_oop for transformation of Synechococcus sp. PCC7002 by chromosomal integration between gene loci A2578 and A2579.
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EXAMPLES
In the following, certain embodiments of the invention will be explained in more detail with reference to figures and experimental data. The figures and examples are not intended to be limiting with respect to specific details. Individual features can be identified with a reference numeral. This does not exclude that more than one of such feature can be present.
Example 1
Plasmid Construction for Synechocystis Sp. PCC 6803
NB: Asterisks (*) mark promoter variants with optimised ribosome binding site.
Construction of plasmid #1145: The pJET base plasmid was designed for genomic integration into Synechocystis sp. PCC 6803. Two regions of homology, glgA-P1 and glgA-P2, corresponding to adjacent upstream and downstream regions of glgA1 (sll1393) gene flank the genetic construct to allow for homologous integration into the glgA1 locus of the Synechocystis sp. PCC 6803 genome. The plasmid was designed with two antibiotic resistance cassettes, the Cm and Amp cassettes, to confer resistance against chloramphenicol and ampicillin, respectively. A genetic insert was generated, comprising the pyruvate decarboxylase gene from Zymomonas mobilis (zmPDC, SEQ ID NO:16) under the transcriptional control of the ziaR-PziaA promoter-regulator gene construct (ziaR-sll0792, ziaA-slr0798, SEQ ID NO:1), to give the first production gene under the transcriptional control of a zinc-inducible promoter. The insert further comprised the second production gene, which was the degenerated gene encoding the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADHdeg, SEQ ID NO:56) under the transcriptional control of the constitutive Prbc promoter. The insert was ligated into the plasmid via SalI and SbfI restriction endonuclease sites. The map of plasmid #1145 is depicted in FIG. 7A, and the sequence is deposited under SEQ ID NO:30. Plasmid annotations are as follows: 3614 . . . 3644 terminator oop; 2603 . . . 3613 CDS synADH\deg; 2308 . . . 2340 terminator oop; 2341 . . . 2599 promoter PrbcL; 8465 . . . 9124 marker Gm; 6774 . . . 7565 recombination insert glgA-P1; 4830 . . . 5687 marker Amp; 567 . . . 2267 CDS zmPDC; 10 . . . 408 CDS ziaR; 416 . . . 559 promoter PziaA; 3651 . . . 4233 recombination insert glgA-P2.
Construction of plasmid #1217: The pVZ325a base plasmid (FIG. 20B, SEQ ID NO:21) was designed for self-replication in Synechocystis sp. PCC 6803. The plasmid was designed with two antibiotic resistance cassettes, the Sp/Sm and the Gm cassettes, to confer resistance against spectinomycin, streptomycin and gentamycin, respectively. A genetic insert was generated (SEQ ID NO:23), comprising the pyruvate decarboxylase gene from Zymomonas mobilis (zmPDC) under the transcriptional control of the corR-PcorT promoter-regulator gene construct (corR-sll0794, PcorT-slr0797, SEQ ID NO:2) as a first production gene under the transcriptional control of a cobalt-inducible promoter, and a second production gene, which was the degenerated gene encoding the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADHdeg) under the transcriptional control of the constitutive Prbc* promoter. The insert was cloned into the plasmid via SalI and SbfI restriction endonuclease sites. The map of plasmid #1217 is depicted in FIG. 8A, and the plasmid sequence is deposited under SEQ ID NO:76. Plasmid annotations are as follows: 3068 . . . 3132 promoter Prbc*; 10317 . . . 10847 CDS Gm; 11185 . . . 12195 CDS Sp/Sm; 1255 . . . 2955 CDS zmPDC; 2981 . . . 3026 dsrA; 4145 . . . 4175 terminator oop; 3134 . . . 4144 CDS synADH\deg; 57 . . . 1166 CDS corR(6803); 1167 . . . 1249 promoter PcorT(6803).
Construction of plasmid #1227: This construct is also based on the pVZ325a base plasmid. A genetic insert was generated (SEQ ID NO:24), comprising the pyruvate decarboxylase gene from Zymomonas mobilis (zmPDC) under the transcriptional control of the nrsR-PnrsB promoter-regulator gene construct (nrsS-sll0798, nrsR-sll0797, nrsB-sll0793, SEQ ID NO:3) as a first production gene under the transcriptional control of a nickel-inducible promoter, and a second production gene, which was the degenerated gene encoding the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (SynADHdeg) under the transcriptional control of the constitutive Prbc* promoter. The insert was cloned into the plasmid via SalI and SbfI restriction endonuclease sites. The map of plasmid #1227 is depicted in FIG. 9. The plasmid sequence is deposited under SEQ ID NO:77. Plasmid annotations are as follows: 2676 . . . 2740 promoter Prbc*; 9925 . . . 10455 CDS Gm; 10793 . . . 11803 CDS Sp/Sm; 863 . . . 2563 CDS zmPDC; 2589 . . . 2634 dsrA; 3753 . . . 3783 terminator oop; 2742 . . . 3752 CDS synADHdeg; 33 . . . 734 CDS nrsR(6803); 736 . . . 855 promoter PnrsB(6803).
Construction of plasmid #1329: This construct is also based on the pVZ325a base plasmid. A genetic insert was generated (SEQ ID NO:26), comprising a first production gene encoding the pyruvate decarboxylase gene from Zymobacter palmae (zpPDC, SEQ ID NO:17) under the transcriptional control of the nickel-inducible nrsR-PnrsB promoter-regulator gene construct, and a second first production gene which was a codon-optimised (for cyanbacterial hosts) version of the gene encoding the pyruvate decarboxylase from Zymomonas mobilis (zmPDC(fco), SEQ ID NO:58) under the transcriptional control of the cobalt-inducible corR-PcorT promoter-regulator gene construct. The codon-optimised zmPDC shares approximately 80-90% sequence identity with the native zmPDC. The map of plasmid #1329 is depicted in FIG. 10A, and the sequence is deposited under SEQ ID NO:73. Plasmid annotations are as follows: 3852 . . . 5561 CDS zmPDC(fco); 5565 . . . 5593 terminator oop; 2661 . . . 3770 CDS corR; 3771 . . . 3853 promoter PcorT; 821 . . . 2500 CDS zpPDC; 11745 . . . 12275 CDS Gm; 12613 . . . 13623 CDS Sp/Sm; 1 . . . 702 CDS nrsR; 2501 . . . 2597 terminator ter; 703 . . . 831 promoter PnrsB. Plasmid #1329 is particularly designed to be transformed into cyanobacterial host cells which harbor at least one additional copy of a recombinant pdc gene in their genome.
Construction of plasmid #1379: This construct is also based on the pVZ325a base plasmid. A genetic insert was generated (SEQ ID NO:29), comprising a first production gene encoding the pyruvate decarboxylase gene from Zymobacter palmae (zpPDC) under the transcriptional control of the nickel-inducible nrsR-PnrsB promoter-regulator gene construct, and a second first production gene which was a degenerated version of the gene encoding the pyruvate decarboxylase from Zymomonas mobilis (zmPDCdeg, SEQ ID NO:18) under the transcriptional control of the corR-PcorT promoter-regulator gene construct. The codon-optimised zmPDC shares approximately 60-65% sequence identity with the native zmPDC. The map of plasmid #1379 is depicted in FIG. 10B, and the sequence is deposited under SEQ ID NO:74. Plasmid annotations are as follows: 5594 . . . 5641 terminator spf; 3887 . . . 5590 CDS zmPDCdeg; 2693 . . . 3802 CDS corR; 3803 . . . 3885 promoter PcorT; 735 . . . 858 promoter PnrsB; 853 . . . 2532 CDS zpPDC; 11788 . . . 12318 CDS Gm; 12656 . . . 13666 CDS Sp/Sm; 33 . . . 734 CDS nrsR; 2533 . . . 2629 terminator ter. Plasmid #1379 is particularly designed to be transformed into cyanobacterial host cells which harbor at least one additional copy of a recombinant pdc gene in their genome.
Construction of plasmid #1389: The plasmid is based on the pJET base vector and was designed as a cloning vector for amplification of constructs to be integrated into the endogenous pSYSG plasmid of Synechocystis sp. PCC 6803 by homologous recombination. A genetic insert was generated (SEQ ID NO:50), comprising a first production gene which was a degenerated version of the gene encoding the encoding the pyruvate decarboxylase gene from Zymobacter palmae (zpPDCdeg, SEQ ID NO:19) under the transcriptional control of the nickel-inducible nrsRS-PnrsB promoter-regulator gene construct. The insert was flanked by two regions of homology, pSYSG-P1 and pSYSG-P2, corresponding to positions slr1816 and sll1817 of pSYSG, to allow for homologous integration into the corresponding endogenous plasmid. The plasmid further harbored Amp and Gm antibiotic resistance cassettes. The map of plasmid #1389 is depicted in FIG. 19A.
Construction of plasmid #1391: The cloning vector for #1391 was generated by first removing the gentamycin resistance cassette Gm from the base vector pVZ325a by a MluI restriction endonuclease digestion/re-ligation, to give the pVZ324a plasmid with remaining Sp/Sm resistance cassette. A genetic insert was generated (SEQ ID NO:51), comprising a first production gene encoding the pyruvate decarboxylase gene from Zymobacter palmae (zpPDC) under the transcriptional control of the cobalt-inducible corR-PcorT promoter-regulator gene construct. The insert was cloned into the plasmid via SalI and SbfI restriction endonuclease sites. The map of plasmid #1391 is depicted in FIG. 19B.
Construction of plasmid #1374: This construct is also based on the pVZ325a base plasmid. A genetic insert was generated, comprising a first production gene encoding the pyruvate decarboxylase gene from Zymobacter palmae (zpPDC, SEQ ID NO:17) under the transcriptional control of the nickel-inducible nrsR-PnrsB promoter-regulator gene construct, and a second first production gene which was a degenerated version of the gene encoding the pyruvate decarboxylase from Zymomonas mobilis (zmPDCdeg, SEQ ID NO:18) under the transcriptional control of the corR-PcorT*1 promoter-regulator gene construct incorporating an optimised ribosome binding site for Synechocystis sp. PCC6803. The map of plasmid #1374 is depicted in FIG. 26. The sequence of plasmid #1374 is deposited under SEQ ID NO:67. Plasmid annotations are as follows: 3858 . . . 3937 promoter PcorT* 1; 5648 . . . 5695 terminator spf\ter; 3938 . . . 5644 CDS zmPDCdeg; 2744 . . . 3856 CDS corR; 909 . . . 2582 CDS zpPDC; 785 . . . 908 promoter PnrsB; 11842 . . . 12372 CDS Gm; 12710 . . . 13720 CDS Sp/Sm; 2583 . . . 2679 terminator ter.
Example 2
Plasmid Construction for Synechococcus sp. PCC 7002
NB: Asterisks (*) mark promoter variants with optimised ribosome binding site.
Construction of plasmid TK115: The pGEM-TK base plasmid was tailored as a cloning vector for amplification of constructs to be homologously recombined into the endogenous plasmid pAQ4 of Synechococcus sp. PCC 7002 (see also FIG. 4 and FIG. 6). Two regions of homology, flanking region pAQ4-FA (751 nt) incorporating NsiI/SalI endonuclease restriction sites (SEQ ID NO:32) and flanking region pAQ4-FB (551 nt) incorporating NotI/SpeI endonuclease restriction sites (SEQ ID NO:35) were designed to integrate into pAQ4 between gene loci SYNPCC7002_D0017 (hypothetical protein, 237 nt, 78 aa) and SYNPCC7002_D0018 (CRISPR-associated protein Cas2, 294 nt, 97 aa). The flanking regions were amplified from pAQ4 by PCR using the primer pairs #323 and #324 (SEQ ID NOs:33 and 34) and #325 and #326 (SEQ ID NOs:36 and 37). The flanking regions pAQ4-FA and pAQ4-FB were then cloned into the pGEM-TK vector via the restriction endonuclease sites NsiI/SalI or NotI/SpeI, respectively. A genetic insert was generated, comprising a first production gene encoding the pyruvate decarboxylase from Zymomonas mobilis (zmPDC) under the transcriptional control of the zinc-inducible smtB-PsmtA promoter-regulator gene construct (SEQ ID NO:4), and a second production gene which was the degenerated gene encoding the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADHdeg) under the transcriptional control of the constitutive Prbc promoter, as well as a neomycin (Nm) resistance cassette. The insert was cloned in between flanking regions pAQ4-FA and pAQ4-FB via restriction endonuclease sites SalI and NotI into the modified pGEM-TK plasmid. The map of plasmid TK115 is depicted in FIG. 14A, and the sequence is deposited under SEQ ID NO:31. Plasmid annotations are as follows: 393 . . . 492 promoter PsmtA; 6 . . . 392 CDS smtB; 4698 . . . 5237 intron pAQ4-FB; 3610 . . . 3670 promoter PpsbA; 3710 . . . 4491 marker Nm; 6105 . . . 6962 marker Amp; 8179 . . . 8915 intron pAQ4-FA; 2276 . . . 2534 promoter PrbcL(6803); 2243 . . . 2275 terminator oop; 2538 . . . 3548 CDS synADHdeg; 3549 . . . 3579 terminator oop; 502 . . . 2202 CDS zmPDC.
Construction of plasmid TK193: The pGEM-TK base plasmid was tailored as a cloning vector for amplification of constructs to be homologously recombined into the endogenous plasmid pAQ3 of Synechococcus sp. PCC 7002 (see also FIG. 4 and FIG. 6). Two regions of homology, flanking region pAQ3-FA incorporating NsiI/SalI endonuclease restriction sites and flanking region pAQ3-FB incorporating NotI/SpeI endonuclease restriction sites were designed to integrate into pAQ3 between gene loci SYNPCC7002_C0006 and SYNPCC7002_C0007 as previously described by Xu and colleagues (2011). The flanking regions were amplified from pAQ3 by PCR using the primer pairs #327 and #328 (SEQ ID NO:38 and SEQ ID NO:39) and #329 and #330 (SEQ ID NO:40 and SEQ ID NO:41). The flanking regions pAQ3-FA and pAQ3-FB were then cloned into the pGEM-TK vector via the restriction endonuclease sites NsiI/SalI or NotI/SpeI, respectively. A genetic insert was generated, comprising a first production gene which was the degenerated version of the gene encoding the pyruvate decarboxylase from Zymobacter palmae (zpPDC) under the transcriptional control of the nickel-inducible nrsRS-PnrsB promoter-regulator gene construct, as well as a gentamycin (Gm) resistance cassette. The insert was cloned in between flanking regions pAQ3-FA and pAQ3-FB via restriction endonuclease sites SalI and NotI into the modified pGEM-TK plasmid. The map of plasmid TK193 is shown in FIG. 23, and the sequence is deposited under SEQ ID NO:52.
Construction of plasmid TK162: The pGEM-TK base plasmid was tailored as a cloning vector for amplification of constructs to be homologously recombined into the endogenous plasmid pAQ3 of Synechococcus sp. PCC 7002 as described above. The plasmid was further furnished with a genetic insert comprising a Pdc gene from Zymomonas mobilis as a first production gene under the transcriptional control of the zinc-inducible smtB-PsmtA promoter-regulator gene construct, and a degenerated version of the gene encoding the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADHdeg) as a second production gene under the transcriptional control of the constitutive PrbcL promoter. The insert was cloned in between flanking regions pAQ3-FA and pAQ3-FB into the modified pGEM-TK plasmid. The map of plasmid TK162 is shown in FIG. 24, and the sequence is deposited under SEQ ID NO:65. Plasmid annotations are as follows: 8408 . . . 8794 CDS smtB; 8795 . . . 8894 promoter PsmtA; 5 . . . 1705 CDS Pdc; 3052 . . . 3082 terminator oop; 2041 . . . 3051 CDS synADH\deg; 1746 . . . 1778 terminator oop; 1779 . . . 2037 promoter PrbcL\6803; 7834 . . . 8402 intron pAQ3-FA; 5760 . . . 6617 marker Amp; 3298 . . . 4306 marker Sp/Sm; 4406 . . . 4892 intron pAQ3-FB.
Construction of plasmids for pAQ1 integration: The pGEM-TK base plasmid was tailored as a cloning vector for amplification of constructs to be homologously recombined into the endogenous plasmid pAQ1 of Synechococcus sp. PCC 7002 (see also FIG. 5 and FIG. 6). Two regions of homology, flanking region pAQ1-FA (SEQ ID NO:42) incorporating NsiI/SalI endonuclease restriction sites and flanking region pAQ1-FB (SEQ ID NO:45) incorporating NotI/SpeI endonuclease restriction sites were designed to integrate into a so far unpublished site of pAQ1 between gene loci SYNPCC7002_B0001 and SYNPCC7002_B0002. The flanking regions were amplified from pAQ1 by PCR using the primer pairs #336 and #337 (SEQ ID NO:43 and SEQ ID NO:44) and #338 and #339 (SEQ ID NO:46 and SEQ ID NO:47). The flanking regions pAQ1-FA and pAQ1-FB were then cloned into the pGEM-TK vector via the restriction endonuclease sites NsiI/SalI or NotI/SpeI, respectively. Genetic inserts were cloned in between flanking regions pAQ1-FA and pAQ1-FB via restriction endonuclease sites SalI and NotI into the modified pGEM-TK plasmid.
Construction of plasmid #1217: The plasmid is based on the pVZ325a plasmid and was designed for self-replication in Synechococcus sp. PCC 7002. It is produced as described for plasmid #1217 in Example 1 and carries two antibiotic resistance markers, a gentamycin (Gm) and a spectinomycin/streptomycin (Sp/Sm) cassette. The map of plasmid #1217 is depicted in FIG. 15.
Construction of plasmid #1356: The plasmid is based on the pVZ325a plasmid and was designed for self-replication in Synechococcus sp. PCC 7002. A genetic insert was generated (SEQ ID NO:57), comprising a first production gene encoding the pyruvate decarboxylase gene from Zymobacter palmae (zpPDC) under the transcriptional control of the nickel-inducible nrsRS-PnrsB* promoter-regulator gene construct, and a second production gene which was a degenerated version of the gene encoding the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADHdeg) under the transcriptional control of the constitutive Prbc* promoter. The insert was cloned into the plasmid via SalI and SbfI restriction endonuclease sites. The plasmid further harbored Gm and Sp/Sm antibiotic resistance cassettes. The map of plasmid #1356 is depicted in FIG. 16A, and the plasmid sequence is deposited under SEQ ID NO:75. Plasmid annotations are as follows: 2304 . . . 3977 CDS zpPDC; 4116 . . . 4180 promoter Prbc*; 11365 . . . 11895 CDS Gm; 12233 . . . 13243 CDS Sp/Sm; 5193 . . . 5223 terminator oop; 4182 . . . 5192 CDS synADH\deg; 3978 . . . 4074 terminator ter; 1476 . . . 2179 CDS nrsR(6803); 2180 . . . 2300 promoter PnrsB*; 117 . . . 1478 CDS nrsS(6803).
Construction of plasmid #1375: The plasmid is based on the pVZ325a plasmid and was designed for self-replication in Synechococcus sp. PCC 7002. A genetic insert was generated (SEQ ID NO:27), comprising a first production gene encoding the pyruvate decarboxylase gene from Zymobacter palmae (zpPDC) under the transcriptional control of the nickel-inducible nrsRS-PnrsB promoter-regulator gene construct, and a second first production gene which was a degenerated version of the gene encoding the pyruvate decarboxylase from Zymomonas mobilis (zmPDCdeg) under the transcriptional control of the cobalt-inducible corR-PcorT* promoter-regulator gene construct. The plasmid further harbored Gm and Sp/Sm antibiotic resistance cassettes. The map of plasmid #1375 is depicted in FIG. 17A.
Construction of plasmid #1376: The plasmid is based on the pVZ325a plasmid and was designed for self-replication in Synechococcus sp. PCC 7002. A genetic insert was generated (SEQ ID NO:28), comprising a first production gene encoding the pyruvate decarboxylase gene from Zymobacter palmae (zpPDC) under the transcriptional control of the nickel-inducible nrsRS-PnrsB* promoter-regulator gene construct, and a second first production gene which was a degenerated version of the gene encoding the pyruvate decarboxylase from Zymomonas mobilis (zmPDCdeg) under the transcriptional control of the cobalt-inducible corR-PcorT* promoter-regulator gene construct. The plasmid further harbored Gm and Sp/Sm antibiotic resistance cassettes. The map of plasmid #1376 is depicted in FIG. 17B.
Construction of plasmid #1381: The plasmid is based on the pVZ325a plasmid and was designed for self-replication in Synechococcus sp. PCC 7002. A genetic insert was generated (SEQ ID NO:48), comprising a first production gene encoding the pyruvate decarboxylase gene from Zymobacter palmae (zpPDC) under the transcriptional control of the nickel-inducible nrsRS-PnrsB promoter-regulator gene construct, and a second first production gene which was a degenerated version of the gene encoding the pyruvate decarboxylase from Zymomonas mobilis (zmPDCdeg) under the transcriptional control of the cobalt-inducible corR-PcorT promoter-regulator gene construct promoter. The plasmid further harbored Gm and Sp/Sm antibiotic resistance cassettes. The map of plasmid #1381 is depicted in FIG. 18A.
Construction of plasmid #1383: The plasmid is based on the pVZ325a plasmid and was designed for self-replication in Synechococcus sp. PCC 7002. A genetic insert was generated (SEQ ID NO:49), comprising a first production gene encoding the pyruvate decarboxylase gene from Zymobacter palmae (zpPDC) under the transcriptional control of the nickel-inducible nrsRS-nrsB* promoter-regulator gene construct, and a second first production gene which was the degenerated version of the gene encoding the pyruvate decarboxylase from Zymomonas mobilis (zmPDCdeg) under the transcriptional control of the cobalt-inducible corR-PcorT promoter-regulator gene construct promoter. The plasmid further harbored Gm and Sp/Sm antibiotic resistance cassettes. The map of plasmid #1383 is depicted in FIG. 18B.
Construction of plasmid #1460: The plasmid is based on the pVZ325a plasmid and was designed for self-replication in Synechococcus sp. PCC 7002. A genetic insert was generated, comprising a first production gene encoding the pyruvate decarboxylase gene from Zymomonas mobilis (zmPDC) under the transcriptional control of the nickel-inducible nrsRS-PnrsB916 promoter-regulator gene construct, and a second production gene which was a degenerated version of the gene encoding the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADHdeg) under the transcriptional control of the constitutive PrbcL* promoter. The insert was cloned into the plasmid via SalI and SbfI restriction endonuclease sites. The plasmid further harbored Gm and Sp/Sm antibiotic resistance cassettes. The map of plasmid #1460 is depicted in FIG. 31A, and the sequence is deposited under SEQ ID NO:68. Plasmid annotations are as follows: 100 . . . 1461 CDS nrsS\(ABCC916); 1458 . . . 2153 CDS nrsR\(ABCC916); 2154 . . . 2282 promoter PnrsB\(ABCC916); 4169 . . . 5179 CDS synADH\deg; 5180 . . . 5210 terminator oop; 4016 . . . 4061 insertion sequence dsrA\ter; 2290 . . . 3990 CDS zmPDC; 12220 . . . 13230 CDS Sp/Sm; 11352 . . . 11882 CDS Gm; 4103 . . . 4167 promoter PrbcL*.
Construction of plasmid #1470: The pGEM-TK base plasmid was tailored as a cloning vector for amplification of constructs to be homologously recombined into the endogenous plasmid pAQ3 of Synechococcus sp. PCC 7002 as already described above. A genetic insert was generated, comprising a first production gene which was the degenerated version of the gene encoding the pyruvate decarboxylase from Zymomonas mobilis (zmPDCdeg) under the transcriptional control of the cobalt-inducible corR-PcorT*1 promoter-regulator gene construct with optimised ribosome binding site, as well as the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADH) as second production gene under the transcriptional control of the constitutive Prbc* promoter. The map of the plasmid is shown in FIG. 32, and the sequence is deposited under SEQ ID NO:69. Plasmid annotations are as follows: 1226 . . . 1305 promoter PcorT* 1; 3016 . . . 3063 terminator spf\ter; 1306 . . . 3012 CDS zmPDCdeg; 112 . . . 1224 CDS corR; 3083 . . . 3147 promoter Prbc*; 3149 . . . 4159 CDS synADH; 4189 . . . 4220 terminator oop; 8956 . . . 9448 intron pAQ3-FB; 7231 . . . 8088 marker Amp; 5446 . . . 6014 intron pAQ3-FA; 4495 . . . 5028 marker Gm.
Construction of plasmid #1473: The pGEM-TK base plasmid was tailored as a cloning vector for amplification of constructs to be homologously recombined into the endogenous plasmid pAQ1 of Synechococcus sp. PCC 7002 as described above. A genetic insert was generated, comprising the pyruvate decarboxylase from Zymomonas mobilis (zmPDC) as a first production gene under the transcriptional control of the nickel-inducible nrsRS-PnrsB916 promoter-regulator gene construct, as well as the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADH) as second production gene under the transcriptional control of the constitutive Prbc* promoter. The map of the plasmid is shown in FIG. 33, and the sequence is deposited under SEQ ID NO:70. Plasmid annotations are as follows: 100 . . . 1461 CDS nrsS\(ABCC916); 1458 . . . 2153 CDS nrsR\(ABCC916); 2154 . . . 2282 promoter PnrsB(ABCC916); 2290 . . . 3990 CDS zmPDC; 4029 . . . 4093 promoter Prbc*; 4095 . . . 5105 CDS synADH; 5135 . . . 5166 terminator oop; 6493 . . . 7000 intron pAQ1-FB2; 7868 . . . 8725 marker Amp; 9942 . . . 10612 intron pAQ1-FA2; 5381 . . . 6389 marker Sp/Sm.
Construction of plasmid #1332: The pGEM-TK base plasmid was tailored as a cloning vector for amplification of constructs to be homologously recombined into the endogenous plasmid pAQ4 of Synechococcus sp. PCC 7002 as described above. A genetic insert comprising a first production gene encoding the pyruvate decarboxylase gene from Zymobacter palmae (zpPDC) under the transcriptional control of the cobalt-inducible corR-PcorT promoter-regulator gene construct, as well as the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADH) as second production gene under the transcriptional control of the constitutive Prbc* promoter with optimised ribosome binding site was inserted. The map of the plasmid is shown in FIG. 34, and the sequence is deposited under SEQ ID No:71. Plasmid annotations are as follows: 2925 . . . 3021 native terminator of zpPDC; 1251 . . . 2924 CDS zmPDC; 1167 . . . 1249 promoter PcorT; 57 . . . 1166 CDS corR; 4147 . . . 4178 terminator oop; 3107 . . . 4117 CDS synADH; 3041 . . . 3105 promoter Prbc*; 8777 . . . 9513 intron pAQ4-FA; 6703 . . . 7560 marker Amp; 4308 . . . 5089 Nm; 4208 . . . 4268 promoter PpsbA; 5296 . . . 5835 intron pAQ4-FB.
Construction of plasmid #1627: The plasmid is based on the pVZ325a plasmid and was designed for self-replication in Synechococcus sp. PCC 7002. The plasmid was furnished with genetic inserts comprising a first production gene encoding the pyruvate decarboxylase gene from Zymomonas mobilis under the transcriptional control of the nickel-inducible PnrsB(ABCC916) promoter and the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADH) as second production gene under the transcriptional control of the constitutive Prbc* promoter with optimised ribosome binding site. The Ni2+ resistance conferring gene cluster nrsRSBAD(ABCC916) that is derived from a Synechococcus species closely related Synechococcus PCC7002 was further inserted. The plasmid map is depicted in FIG. 35, and the sequence is deposited under SEQ ID NO:72. Plasmid annotations are as follows: 1889 . . . 1957 promoter Prbc*(optRBS); 1843 . . . 1888 insertion sequence dsrA ter; 1958 . . . 2968 CDS synADH; 2998 . . . 3028 terminator oop; 117 . . . 1817 CDS PDC; 9170 . . . 9700 CDS Gm; 10428 . . . 11789 CDS nrsS(ABCC916); 11786 . . . 12481 CDS nrsR(ABCC916); 12611 . . . 13294 CDS nrsB(ABCC916); 13338 . . . 16505 CDS nrsA(ABCC916); 16628 . . . 17290 CDS nrsD(ABCC916); 17321 . . . 17941 CDS nrsD′(ABCC916); 6 . . . 109 promoter PnrsB\ABCC916.
Construction of plasmid #1480: The plasmid was tailored as a cloning vector for amplification of constructs to be homologously recombined into the endogenous plasmid pAQ3 of Synechococcus sp. PCC 7002 as described above. The plasmid was further furnished with a genetic insert comprising a degenerated version of the pyruvate decarboxylase gene from Zymomonas mobilis (zmPDCdeg) as a first production gene under the transcriptional control of the zinc-inducible aztR-PaztA promoter-regulator gene construct from Anabaena PCC7120, as well as the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADH) as second production gene under the transcriptional control of the constitutive PrbcL* promoter. The map of the plasmid is shown in FIG. 38A, and the sequence is deposited under SEQ ID No:78. Plasmid annotations are as follows: 3830 . . . 4363 marker Gm; 4781 . . . 5349 intron pAQ3-FA; 6566 . . . 7423 marker Amp; 8291 . . . 8783 intron pAQ3-FB; 3524 . . . 3555 terminator oop; 2484 . . . 3494 CDS synADH; promoter 2418 . . . 2482 PrbcL*; 2351 . . . 2398 terminator spf; 97 . . . 507 CDS aztR(7120); 520 . . . 642 promoter PaztA(7120); 641 . . . 2347 CDS zmPDCdeg.
Construction of plasmid #1563: The plasmid pGEM was tailored as a cloning vector for amplification of constructs to be homologously recombined into the Synechococcus sp. PCC 7002 chromosome between gene loci A0124 and A0125. Two regions of homology, P-A1 and P-A2, flank the genetic construct to allow for chromosomal homologous integration. The plasmid was furnished with a genetic insert comprising a pyruvate decarboxylase gene from Zymomonas mobilis (zmPDC) as a first production gene under the transcriptional control of the zinc-inducible smtB-PsmtA promoter-regulator gene construct, as well as the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADH) as second production gene under the transcriptional control of the constitutive Prbc* promoter. The map of the plasmid is shown in FIG. 39A, and the sequence is deposited under SEQ ID No:79. Plasmid annotations are as follows: 4739 . . . 6059 intron P-A2; 3621 . . . 4629 marker Sp/Sm; 6906 . . . 7763 marker Amp; 3375 . . . 3406 terminator oop; 2335 . . . 3345 CDS synADH; 2269 . . . 2333 promoter Prbc*, 6 . . . 392 CDS smtB; 393 . . . 492 promoter PsmtA; 2216 . . . 2240 terminator dsrA; 502 . . . 2204 CDS zmPDC; 8981 . . . 10291 intron P-A1.
Construction of plasmid #1568: The plasmid pGEM was tailored as a cloning vector for amplification of constructs to be homologously recombined into the Synechococcus sp. PCC 7002 chromosome between gene loci A1330 and A1331. Two regions of homology, P-B1 and P-B2, flank the genetic construct to allow for chromosomal homologous integration. The plasmid was furnished with a genetic insert comprising a degenerated pyruvate decarboxylase gene from Zymomonas mobilis (zmPDCdeg) as a first production gene under the transcriptional control of the zinc-inducible smtB-PsmtA promoter-regulator gene construct, as well as the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADH) as second production gene under the transcriptional control of the constitutive Prbc* promoter. The map of the plasmid is shown in FIG. 39B, and the sequence is deposited under SEQ ID No:80. Plasmid annotations are as follows: 4447 . . . 5530 intron P-B2; 8452 . . . 9516 intron P-B1; 66 . . . 392 CDS smtB; 393 . . . 492 promoter PsmtA; 3684 . . . 4217 marker Gm; 6747 . . . 7604 marker Amp; 3378 . . . 3409 terminator oop; 2338 . . . 3348 CDS synADH; 2272 . . . 2336 promoter Prbc*; 2205 . . . 2252 terminator spf; 495 . . . 2201 CDS zmPDCdeg.
Construction of plasmid #1692: The plasmid pGEM was tailored as a cloning vector for amplification of constructs to be homologously recombined into the Synechococcus sp. PCC 7002 chromosome between gene loci A2578 and A2579. Two regions of homology, P-C1 and P-C2, flank the genetic construct to allow for chromosomal homologous integration. The plasmid was furnished with a genetic insert comprising a pyruvate decarboxylase gene from Zymomonas mobilis (zmPDC) as a first production gene under the transcriptional control of the zinc-inducible smtB-PsmtA promoter-regulator gene construct, as well as the degenerated alcohol dehydrogenase gene from Synechocystis sp. PCC 6803 (synADHdeg) as second production gene under the transcriptional control of the constitutive PrbcL promoter. The map of the plasmid is shown in FIG. 39C and the sequence is deposited under SEQ ID No:81. Plasmid annotations are as follows: 4691 . . . 5875 intron P-C2; 3710 . . . 4491 marker Nm; 7283 . . . 8140 marker Amp; 9357 . . . 10553 intron P-C1; 502 . . . 2202 CDS zmPDC; 3549 . . . 3579 terminator oop; 2538 . . . 3548 CDS synADHdeg; 2243 . . . 2275 terminator oop; 2276 . . . 2534 promoter PrbcL(6803); 6 . . . 392 CDS smtB; 393 . . . 492 promoter PsmtA.
Construction of plasmid #1564: The plasmid pGEM was tailored as a cloning vector for amplification of constructs to be homologously recombined into the Synechococcus sp. PCC 7002 chromosome between gene loci A0124 and A0125 as described above. A genetic insert comprising a pyruvate decarboxylase gene from Zymomonas mobilis (zmPDC) as a first production gene under the transcriptional control of the cobalt-inducible corR-PcorT promoter-regulator gene construct, as well as the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADH) as second production gene under the transcriptional control of the constitutive Prbc* promoter were inserted between flanking regions P-A1 and P-A2. The map of the plasmid is shown in FIG. 41A, and the sequence is deposited under SEQ ID No:82. Plasmid annotations are as follows: 1167 . . . 1249 promoter PcorT(6803); 57 . . . 1166 CDS corR(6803); 2969 . . . 2993 terminator dsrA; 1255 . . . 2957 CDS zmPDC; 9734 . . . 11044 intron P-A1; 3022 . . . 3086 promoter Prbc*; 3088 . . . 4098 CDS synADH; 4128 . . . 4159 terminator oop; 7659 . . . 8516 marker Amp; 4374 . . . 5382 marker Sp/Sm; 5492 . . . 6812 intron P-A2.
Construction of plasmid #1633: The plasmid pGEM was tailored as a cloning vector for amplification of constructs to be homologously recombined into the Synechococcus sp. PCC 7002 chromosome between gene loci A1330 and A1331 as outlined above. The plasmid was further furnished with a genetic insert comprising a degenerated pyruvate decarboxylase gene from Zymomonas mobilis (zmPDCdeg) as a first production gene under the transcriptional control of the cobalt-inducible corR-PcorT*1 promoter-regulator gene construct with optimised ribosome binding site, as well as the alcohol dehydrogenase from Synechocystis sp. PCC 6803 (synADH) as second production gene under the transcriptional control of the constitutive Prbc* promoter. The map of the plasmid is shown in FIG. 41B, and the sequence is deposited under SEQ ID No:83. Plasmid annotations are as follows: 54 . . . 1166 CDS corR(6803); 1168 . . . 1247 promoter PcorT* 1; 5200 . . . 6283 intron P-B2; 9205 . . . 10269 intron P-B1; 4437 . . . 4970 marker Gm; 7500 . . . 8357 marker Amp; 4131 . . . 4162 terminator oop; 3091 . . . 4101 CDS synADH; 3025 . . . 3089 promoter Prbc*; 2958 . . . 3005 terminator spf; 1248 . . . 2954 CDS zmPDCdeg.
Construction of plasmid #1574: The plasmid pGEM was tailored as a cloning vector for amplification of constructs to be homologously recombined into the Synechococcus sp. PCC 7002 chromosome between gene loci A2578 and A2579 as described above. A genetic insert comprising a pyruvate decarboxylase gene from Zymobacter palmae (zpPDC) as a first production gene under the transcriptional control of the cobalt-inducible corR-PcorT promoter-regulator gene construct, as well as the degenerated alcohol dehydrogenase gene from Synechocystis sp. PCC 6803 (synADHdeg) as second production gene under the transcriptional control of the constitutive Prbc* promoter were inserted between the flanking regions p-C1 and P-C2. The map of the plasmid is shown in FIG. 41C and the sequence is deposited under SEQ ID No:84. Plasmid annotations are as follows: 5259 . . . 6443 intron P-C2; 4117 . . . 4147 terminator oop; 3106 . . . 4116 CDS synADHdeg; 4278 . . . 5059 marker Nm; 7851 . . . 8708 marker Amp; 9925 . . . 11121 intron P-C1; 3040 . . . 3104 promoter Prbc*; 56 . . . 1165 CDS corR(6803); 1166 . . . 1248 promoter PcorT(6803); 1250 . . . 2923 CDS zpPDC; 2924 . . . 3020 terminator ter.
Example 3
Transformation of Synechocystis sp. PCC 6803 by Spontaneous DNA Uptake
Synechocystis sp PCC 6803 is a naturally competent bacterium and is characterised by spontaneous uptake of free DNA without any pre-treatment. For transformation, 10 ml of the bacterial culture in a logarithmic growth phase (OD750nm ̃0.8) were centrifuged for 10 min at 4000 rpm. The bulk of the supernatant was discarded and the bacterial pellet was resuspended in the remaining supernatant (approximately 100-200 μl). The resulting bacterial culture concentrate was then incubated with approximately 500-1000 ng of the respective transformable DNA for 1-2 hours under non-selective conditions, i.e. no shaking and low-light conditions (25-35 μmol m−2 sec−1), before being plated on BG11-1% cyanoagar without the addition of antibiotics. After 2 days of incubation at 28° C. (25-35 μmol m−2 sec−1 PPF), selection conditions were applied by adding the corresponding antibiotic(s) underneath the agar to form a gradient concentration of antibiotic(s). Colony growth on agar plates under selection conditions allowed for positive selection of transformants.
Example 4
Transformation of Synechocystis sp. PCC 6803 by Conjugation
The transformation of Synechocystis sp. PCC 6803 by conjugation followed the procedure described by Zinchenko et al. (1999). 3 ml overnight cultures were inoculated with E. coli strain XL-1 carrying the cargo plasmid (pVZ) and E. coli strain J53 [RP4]. The culture was supplemented with appropriate antibiotics (50 μg/ml ampicillin and 20 μg/ml kanamycin for E. coli J53 [RP4], and the construct-specific antibiotic for E. coli carrying the respective cargo plasmid pVZ). 250 μl of the overnight culture were mixed with about 10 ml LB medium without antibiotics and further cultured in 100 ml Erlenmeyer flasks for another 2.5 hours at 37° C. with shaking. Bacteria were harvested by centrifugation in two 15 ml falcon tubes at 2500 rpm for 8 min at room temperature in a Hettich Rotina 240R centrifuge. The bacterial pellets were resuspended in 1 ml LB medium each, then mixed together in 2 ml Eppendorf tubes and centrifuged again (5 min, 2500 rpm in Hettich Mirco 200R centrifuge). The resulting pellet was resuspended in 100 μl LB medium and incubated without shaking 1 h at 30° C. Next, 1.9 ml Synechocystis culture of a mid-log growth phase (OD ̃0.8), was added, shaken slightly and centrifuged. The pellet was resuspended in approximately 50 μl BG-11 medium and dispensed dropwise on a HATF (nitrocellulose membrane) filter (Millipore Durapore Membrane Filter, 0.22 μm), which was located on a prepared culture plate (of 20 ml 2×BG-11 medium, 20 ml cyanoagar and 2 ml LB medium). Incubation for 2 days under low light conditions (25-35 μmol m−2 sec−1) at 28° C. was maintained. Afterwards, the cells were released from the membrane filter by in 200 μl BG-11 medium. Different dilutions of the cell suspension (1:10 or 1:100) were plated on 1%-cyano agar plate with antibiotic (for Synechocystis PCC 6803: Streptomycin 2 μg/ml, Gentamycin 2 μg/ml, Kanamycin 10 μg/ml). After approximately 10 days, first transconjugants became visible. A further week later, single colonies were transferred to plates with higher concentrations of antibiotics (e.g. Gentamycin and Streptomycin 5 μg/ml).
Example 5
Quantitative Determination of Acetaldehyde and/or Ethanol Content in Growth Media by Headspace as Chromatography (GC Online Measurement)
In a typical experiment for the quantitative determination of acetaldehyde and/or ethanol content in growth media by headspace gas chromatography (GC), the ethanol production of the respective cyanobacterial culture has to be induced 1-3 days prior to the GC measurement to trigger the overexpression of the pdc and Synadh production genes. For instance, the induction of the ziaA promoter occurred under zinc addition whereas the corT and the nrsB promoter were induced by cobalt and nickel addition, respectively. The induced hybrid cells were either scratched from BG11 plates or harvested from liquid cultures by centrifugation and then resuspended in appropriate fresh marine medium ensuring that the induction conditions were maintained (e.g. mBG11 with 10 μM zinc sulfate prepared with artificial seawater, or an instant ocean supplement for ziaA promoter). The medium was further supplemented with 50 mM TES, pH 7.3 and 20 mM NaHCO3. The sample was adjusted to an OD750nm of about 1.2 mL sample were then aliquoted per 20 mL GC vial loaded with 3 ml pure CO2. The tightly closed GC vials were placed onto the illuminated (150 μE M−2 s−1) headspace auto sampler and were analyzed on the same day on a Shimadzu GC-2010 gas chromatograph equipped with medium-bore capillary column (FS-CS-624, length 30 m; I.D. 0.32 mm; film 1.8 μm) and flame ionisation detector. After completion of the GC measurements, the final OD750nm was determined to normalise the ethanol production rate according to the average OD750nm of the bacterial sample. The average OD750nm was calculated as the arithmetic mean of the OD750nm at the time of sample preparation and the OD750nm after completion of the GC measurement.
Example 6A
Validation of the ziaR-PziaA Promoter Specificity and Tightness in Synechocystis sp. PCC6803
A prerequisite for the inventively-used serial induction of different inducible promoters is a high specificity of each promoter to the respective inductor, as well as a tight repression of each promoter in its uninduced state. This prerequisite was tested for each of the metal-inducible promoters that were incorporated in the genetic constructs for the generation of metabolically enhanced Synechocystis sp. PCC 6803 set forth in Example 1. Particular focus was given to a potential cross-reactivity of different promoters upon addition of the respective alternative, i.e. unrelated, inductors. In FIG. 7B, the ethanol production of the ethanologenic, chromosome-integrative strain #1145 (for plasmid map refer to FIG. 7A, for nucleotide sequence see SEQ ID NO:30) is depicted that was analyzed by GC online measurements in the presence of either 10 μM Co2+, 10 μM Ni2+ or 10 μM Zn2+, as well as without added metal-ions. The result shows that the ziaR-PziaA promoter regulating the recombinant pdc as first production gene in strain #1145 is very specific for zinc as the inductor, leading to a substantial ethanol production exclusively upon addition of zinc. Thus, the ziaR-PziaA promoter is well suited for use in metabolically enhanced cyanobacteria according to the present invention.
Example 6B
Validation of the corR-PcorT Promoter Specificity and Tightness in Synechocystis sp. PCC6803
FIG. 8B shows the ethanol production of the ethanologenic hybrid strain carrying the extrachromosomal plasmid #1217 (for plasmid map refer to FIG. 8A, for nucleotide sequence see SEQ ID NO:23) analyzed by GC online measurement in the presence of either 10 μM Co2+, 10 μM Ni2+ or 10 μM Zn2+, as well as without added metal-ions. The results proof that the corR-PcorT promoter regulating the pdc gene on plasmid #1217 responds very specific to cobalt, leading to a substantial ethanol production exclusively upon addition of cobalt. Therefore, the corR-PcorT promoter tested in this experiment is particularly suitable for use in metabolically enhanced cyanobacteria according to the invention.
Example 6C
Validation of the nrsR-PnrsB Promoter Specificity and Tightness in Synechocystis sp. PCC6803
Finally, also the nrsR-PnrsB promoter was tested regarding its specificity and tightness. The ethanol production of the ethanologenic strain #1227 (for plasmid map refer to FIG. 9A, for nucleotide sequence see SEQ ID NO:24) is pictured in FIG. 9B. The ethanol production was analyzed by GC online measurements in the presence of either 10 μM Co2+, 10 μM Ni2+ or 10 μM Zn2+, as well as without added metal-ions. The results demonstrate that the nrsR-PnrsB promoter is very tight as long as no nickel is present in the growth medium. Upon nickel addition, the ethanol production increases significantly. Since the nrsR-PnrsB promoter responds specifically to the presence of nickel, it is, too, well-suitable for use in metabolically enhanced cyanobacteria according to the present invention.
Example 7
Generation of Metabolically Enhanced Synechocystis sp. PCC 6803 Hybrid Strains with Multiple First Production Genes and a Second Production Gene
Synechocystis sp. PCC 6803 was transformed with constructs #1145 and #1329 to generate and test a metabolically enhanced cyanobacterium harboring three first production genes under the transcriptional control of different inducible promoters and a second production gene under the transcriptional control of a constitutive promoter. First, Synechocystis sp. PCC 6803 was transformed with the integrative construct #1145 (pJET-glgA::ziaR-PziaA-ZmPDC-PrbcL-synADH(deg)-Cm) via natural DNA uptake as described in Example 3. The plasmid map is shown in FIG. 7A, and the nucleotide sequence is deposited as SEQ ID NO:30. By homologous recombination with the genomic DNA the ΔglgA (sll1393) mutant containing the ethanologenic gene cassette under control of the zinc-inducible ziaR-PziaA promoter was generated (ΔglgA::ziaR-PziaA-ZmPDC-PrbcL-synADHdeg). After checking for correct replacement of the wild type version against the hybrid version and full segregation of the transformants by a specific polymerase chain reaction, the self-replicating plasmid #1329 (pVZ325a-nrsR-PnrsB-zpPDC-corR_PcorT-zmPDC(fco)) was introduced into the ethanologenic ΔglgA mutant by conjugation as described in Example 4. The plasmid comprised two different pdc copies, namely the pdc from Zymobacter palmae and a codon optimized pdc from Zymomonas mobilis, under control of two different promoters, namely the nrsR-PnrsB and corR-PcorR. The map of plasmid #1329 is shown in FIG. 10A and corresponding DNA sequence is provided as SEQ ID NO:26. The presence of all the three different promoter-pdc constructs in the transformants was verified by PCR. The production gene assembly in the metabolically enhanced hybrid strain Synechocystis sp. PCC 6803 #1145/#1329 is schematically represented in FIG. 11A, i.e. one genomic integration of a pdc gene and an adh gene as well as two pdc genes on the pVZ vector #1329.
As a second variant of metabolically enhanced Synechocystis sp. PCC 6803 according to the present invention, a hybrid strain comprising the integrative construct #1389 for the endogenous plasmid pSYSG in addition to the ethanologenic chromosome-integrative construct #1145 and a self-replicating pVZ plasmid #1391 was generated. The map of construct #1389, an integrative vector for pSYSG is shown in FIG. 19A and the corresponding DNA sequence is provided as SEQ ID NO:50. The Synechocystis sp. PCC 6803 hybrid thus carried the chromosome-integrative construct #1145 with the Zymomonas mobilis pdc gene under the transcriptional control of the zinc-inducible ziaR-PziaA promoter as a first production gene, the replicative pVZ vector #1391 with the Zymobacter palmae pdc under the transcriptional control of the cobalt-inducible corR-PcorT promoter as the second first production gene and the pSYSG construct #1389 with the degenerated Zymobacter palmae pdc under the transcriptional control of the nickel-inducible nrsRS-PnrsB promoter as the third first production gene, as is schematically shown in FIG. 21.
As a third variant of metabolically enhanced Synechocystis sp. PCC 6803 according to the present invention, a hybrid strain comprising the ethanologenic chromosome-integrative construct #1145 and the self-replicating pVZ plasmid #1374 was generated. The map of plasmid #1374 is shown in FIG. 26 and the corresponding DNA sequence is provided as SEQ ID NO:67. As is schematically summarised in FIG. 27A, the Synechocystis sp. PCC 6803 hybrid #1145/1373 thus harboured three independently inducible pdc gene copies, namely the Zymomonas mobilis Pdc gene under the transcriptional control of the zinc-inducible ziaR-PziaA promoter as a first production gene, the Zymobacter palmae Pdc under the transcriptional control of the nickel-inducible nrsRS-PnrsB promoter as the second first production gene and the degenerated Zymomonas mobilis Pdc under the transcriptional control of the cobalt-inducible corR-PcorT*1 promoter as the third first production gene.
Example 8
Metabolic Characterisation of the Enhanced Synechocystis sp. PCC 6803 Hybrid Strains with Multiple First Production Genes and a Second Production Gene
The transformant Synechocystis sp. PCC 6803 #1145/#1329 described in Example 7 was tested for EtOH production under specific induction conditions in GC online measurements (FIG. 11C). In a control experiment, the Synechocystis sp. PCC 6803 transconjugant carrying only plasmid #1329 was analysed as reference (FIG. 11B). The results show that ziaR-PziaA was repressed under non-induced conditions, i.e. in absence of Zn-salts, and induced in presence of Zn-salts. Accordingly, nrsR-PnrsB was repressed in the absence of Ni-salts and in the presence of Zn-salts, respectively, and was specifically induced by the presence of Ni2+. CorR-PcorT was not induced in absence of Co-salts and upon addition of Zn-salts or Ni-salts, respectively, but was solely induced upon addition of Co2+. As long as neither zinc nor cobalt or nickel were present in the growth medium, all three pdc genes remained silent, i.e. no significant EtOH production (<0,0005% v/v EtOH per OD750nm) was detectable as a results of the very tight repression of the promoters used. As shown in FIG. 11B, the EtOH production of the reference strain comprising only the extrachromosomal pVZ plasmid #1329 is exclusively induced upon Ni and Co addition, respectively, whereas addition of Zn shows no effect. This results proofs that the additional pdc gene present in the genome of strain #1145/1329 but not in strain #1329 responds specifically to zinc addition. In conclusion, this example and the examples set forth above demonstrated the monospecificity of the three different metal-ion inducible promoters, and further demonstrated that cyanobacterial hybrid strains can be generated comprising at least three different first production genes which can be selectively and sequentially induced via their specific different promoters. FIGS. 12A and 12B show related GC online data from strain #1145/1329. In this experiment the strain #1145/1329 was not pre-induced on agar plates and the cells were accordingly not induced until the transfer to the GC vials that were supplemented with different combinations of zinc, cobalt and nickel. As evident from FIG. 12A, in the vial without added metal-ions almost no ethanol is produced, whereas in both vials with either nickel or cobalt supplementation, ethanol production is induced after a lag phase of about 30 hours. If nickel and cobalt were simultaneously supplemented, the ethanol production was significantly higher than in the vial with only one of both metal-ions added, indicating that two pdc genes were induced at the same time. FIG. 11B shows that similar behaviours were observed for the separate addition of zinc and cobalt in comparison to zinc plus cobalt: Simultaneous addition of zinc and cobalt resulted in a higher ethanol production rate than found for the separate addition of either one of the metal ions. In conclusion, also the data shown in FIGS. 12A and 12B indicate that each of the three pdc genes present in strain #1145/1329 can be selectively induced by the addition of the respective metal ion, thus providing the prerequisite of a selective sequential induction of the three first production genes according to the present invention to minimise genetic alteration and prolong the duration of ethanol production. FIG. 13 shows the results of an experiment investigating the accumulated Pdc activities upon simultaneous induction of different promoters of the three pdc production genes in strain #1145/1329. As expected, simultaneous addition of zinc, nickel and cobalt resulted in the highest Pdc activity, followed by the dual induction compared the sole addition of each metal ion. If none of the metal ions was added, the Pdc activity remained very low, demonstrating the tight repression of all three used inducible promoters.
Furthermore, the alternative transformant Synechocystis sp. PCC 6803 #1145/#1374 described in Example 7 was also tested for EtOH production under specific induction conditions in GC online measurements, following the general procedure described above. The results are shown in FIG. 27B and FIG. 27C. FIG. 27B shows the results of ethanol production in % (v/v) ethanol per culture OD over time of Synechocystis PCC6803 #1145/1374, as determined by GC online measurement under different induction conditions. It was found that addition of 15 μM Zn (crosshair markers), 5 μM Ni (triangle markers) and 5 μM Co (square markers), respectively, led to specific induction of the corresponding Pdc gene, so that ethanol production took place. In contrast, insignificant ethanol production was observed in the absence of these metals in the control experiment (diamond markers). These findings demonstrated that also in this alternative hybrid strain the Zn, Co, and Ni inducible promoters were selectively addressable by the respective metal ions, with no significant cross-induction detectable. Each of the three promoters specifically drove its operably linked production gene upon induction, as required according to the present invention and supports the specific response of each metal inducible promoter to its specific metal-ion in Synechocystis sp. PCC6803, as was already demonstrated in Example 6 above. FIG. 27C shows the Pdc activity in μmol per minute and milligram protein measured for Synechocystis PCC6803 #1145/1374 grown under selective induction conditions. In contrast to the control without addition of metal ions, which exhibits a very low Pdc activity, addition of Ni2+, Co2+ and Zn2+, respectively, leads to specific induction of one of the three present Pdc copies.
Example 9
Culture Monitoring
The status of culture with respect to genetic integrity of the production genes and/or productivity of the first chemical compound is continuously or semi-continuously controlled by culture monitoring in order to track the productivity of the culture over the whole production period and to take timely measures upon productivity decrease. Amongst other techniques, culture monitoring included pdc enzyme activity tests as well as determination of ethanol content in the growth media by headspace gas chromatography. In addition, mutations in the pdc gene(s) were monitored by sequencing, enzymatic mismatches detection and/or melting point mismatch detection as well as combinations thereof.
Pdc activity test: The procedure investigates the activity of the overexpressed enzyme pyruvat decarboxylase (Pdc) in induced, ethanol producing cultures. The assay is an optical-enzymatic test wherein the kinetic reaction can be recorded using a spectrophotometer that measures absorbance of a sample over time. Pyruvate is enzymatically converted to acetaldehyde by Pdc, which is reduced to ethanol by ethanol dehydrogenase under NADH oxidation. The determined Pdc activity is related to the protein content, which is measured by Lowry protein assay for determining the total level of protein in solution. For further laboratory reference see for instance Hoppner et al. (1983).
Enzymatic mismatch detection: Enzymatic mismatch detection is performed according to Qiu et al. using the Surveyor Mutation Detection Kit (Transgenomic, NE, USA) according to the manufacturer's instructions. Briefly, the mismatch specific CEL-1 endonuclease from celery rods recognizes mismatches in fragments up to 2 kb. The amplification of two overlapping fragments of the pdc gene is necessary to cover the whole gene sequence. CEL-1 cleaves with high specificity at the 3′-end of any mismatch site in both DNA strands, i.e. base substitutions and insertions or deletions of nucleotides are recognized. To this end, whole DNA is prepared from the bacterial culture in regular intervals throughout the cultivation. Afterwards, the non-mutated and mutated pdc gene copies are amplified by conventional PCR. Next, both types of amplified products are denatured and then re-annealed under non-stringent conditions, leading to mismatched DNA-hybrids consisting of one strand of the original pdc gene and one strand of the mutant version. The DNA-hybrids are then digested with CEL-I endonuclease, leading to a degree of DNA fragmentation proportional to the extent of mutations accumulated in the pdc gene. The degree of DNA fragmentation is determined by DNA gel electrophoresis.
Example 10
Long-term Cultivation of Metabolically Enhanced Synechocystis sp. PCC 6803 Strain #1145/#1374 with Sequential Induction of Multiple First Production Genes
Synechocystis sp. PCC 6803 strain #1145/#1374 as well as strain #1145 as a control were grown as pre-cultures in mBG11 liquid medium supplemented with gentamycin and chloramphenicol (strain #1145 only with chloramphenicol) to apply selection pressure for constructs #1145 and #1374. Neither Zn, Ni or Co were added to the culture at this stage in order to avoid diverting fixed-carbon from cell growth, but to grow the uninduced culture to a high cell density. Upscale of the pre-culture in a main culture using mBG-11 medium (35 psu, artificial seawater salts) without addition of metal ions (Zn, Ni, Co) maintained repression of the three different promoters PziaA, PnrsB and PcorT* 1. For plasmid maintenance and contamination control, chloramphenicol in a concentration of 100 mg L−1 for #1145 and gentamycin in a concentration of 200 mg L−1 for #1145/1374 was used.
Cells were cultivated in 0.5 L round bottles with a culture volume of 0.4 L. Mixing was achieved with a magnetic stir bar at 250 rpm, applied continuously. A light/dark photoperiod of 12 h/12 h was used. Illumination of the cultures was realized by fluorescence lamps (Sylvania Grolux FHO 39W/T5/GRO). The light intensity was dynamically adjusted according to the cell density, increasing from 140 μE m-2 s−1 to up to 450 μE m-2 s−1, whilst illumination was provided from two sides of the culture vessels. The temperature regime was set to 25-28° C. during the dark phase and 36-39° C. during the light phase. CO2 enriched air was bubbled through the cultures by injection of 0.5% CO2 at a flow rate of 20 mL min−1.
The results of this long-term cultivation experiment are shown in FIGS. 28A and B, FIGS. 29A and B and FIGS. 30A and B. FIG. 28A shows the development of culture cell density as OD750nm over the cultivation time in days for the hybrid strain #1145/#1374, whereas FIG. 28B shows the same measurement for the control strain #1145. FIG. 29A shows the corresponding ethanol production in % (v/v) for the hybrid strain #1145/#1374 in this experiment, whereas FIG. 29B shows this measurement again for the control strain #1145. FIG. 30A additionally shows the corresponding ethanol production in % (v/v) normalised to the culture OD for the hybrid strain #1145/#1374 in this experiment, whereas FIG. 30B shows this measurement again for the control strain #1145. The graphs represent the results from double-experiments using biological replicates.
As can be seen in FIGS. 28A, 29A and 30A, the experiment was performed for a total cultivation period of about eight weeks. During the first 14 days of cultivation, the cells were induced by zinc addition. For this purpose, 5 μM zinc sulfate was added to the culture on the first cultivation day, and further 10 μM zinc sulfate on the second cultivation day, to give 15 μM zinc sulphate in total. Thenceforth the productivity of the culture was monitored. After about two weeks, a stagnation or decline of the cell density and/or ethanol productivity was detected. Hereupon, a medium exchange was performed by spinning the culture down at 6500 rpm for 10 minutes and replacing the supernatant using fresh mBG-11 medium, thereby adjusting the cell density to an OD750nm of about 1. A recovery phase of about one week, illustrated by the dashed vertical lines with the bold arrows in between, was maintained under repressed conditions, i.e. without addition of Zn, Co or Ni. Afterwards, the second induction was then realized by addition of 5 μM cobalt sulphate. After approximately two weeks of cultivation under induced conditions, a stagnation or decline of the cell density and/or ethanol productivity was again detected which was again followed by a medium exchange as outlined above, and one week cultivation under repressed condition for culture recovery. Finally, the third induction was subsequently accomplished with addition of 5 μM nickel sulfate. Accordingly, a third ethanol production phase was observed, until after about two weeks further cultivation time, corresponding to a total cultivation time of approximately 60 days, a stagnation or decline of the cell density and/or ethanol productivity was again detected and the experiment was terminated.
As can be derived from FIGS. 28B, 29B and 30B for the cultivation of the control strain #1145, which contains only one Pdc gene and was cultivated in parallel and treated in the same way as done with the ethanologenic strain #1145/1374, only one first ethanol production phase of about two weeks was observed with this strain.
In summary, the serial induction of the three inducible promoters controlling the recombinant first production genes in Synechocystis sp. PCC 6803 strain #1145/#1374 allowed to significantly prolong the production period with the metabolically enhanced cyanobacterium set forth by the present invention when compared to a hybrid strain harbouring only one production gene.
It should be noted that the medium exchange used in the present example may be omitted by directly adding the second or further inducing agent to the culture without the need to remove previously added inducing agent by change of medium.
Example 11
Generation of Metabolically Enhanced Synechococcus Sp. PCC 7002
Synechococcus PCC 7002 was transformed with an ApaI/NsiI digested TK115 construct (pGEM-pAQ4::smtB-PsmtA-PDC-PrbcL-synADHdeg) via natural DNA uptake as set forth in Example 3 for Synechocystis sp. PCC 6803. The ApaI/NsiI part of TK115 contains regions of pAQ4 which flank the ethanologenic gene cassette and its promoter smtB-PsmtA (Zn inducible). By homologous recombination with the endogenous pAQ4 plasmid, a transformant comprising smtB-PsmtA-PDC-PrbcL-synADHdeg was generated. For further details refer to the plasmid map of TK115 (FIG. 14A) and the corresponding SEQ ID NO:31, as well as to the corresponding section for TK115 of Example 2. After checking for the correct replacement of the wild type version against the hybrid version, Synechococcus sp. PCC 7002 strain TK115 was tested for EtOH production under induction conditions (10 μM Zn) by GC online measurements. After addition of Zn, the Synechococcus sp. PCC 7002 strain TK115 strain produced EtOH with a rate of  ̃0.01% (v/v) OD−1 d−1. Without Zn and in the presence of Co and Ni the smtB-PsmtA promoter was tight (FIG. 14B).
Example 12
Generation of Metabolically Enhanced Synechococcus sp. PCC 7002 Hybrid Strains with Different Combinations of Multiple First Production Genes and at Least One Second Production Gene
Synechococcus sp. PCC 7002 strain TK115 was transformed by conjugation according to the method detailed in Example 4 for Synechocystis sp. PCC 6803, except that a specific medium for transformation of Synechococcus sp. PCC 7002 (according to Stevens et al. 1973) was used for growing Synechococcus sp. PCC 7002 prior to conjugation. A variety of different self-replicating ethanologenic pVZ plasmids harboring different combinations of pdc production genes and inducible promoters were used. The following plasmids were tested: #1375 (FIG. 17A, SEQ ID NO:27), #1376 (FIG. 17B, SEQ ID NO:28), #1381 (FIG. 18A, SEQ ID NO:48) and #1383 (FIG. 18B, SEQ ID NO:49). All plasmids contained two different pdc copies: the native version from Zymobacter palmae and a degenerated version of the Zymomonas mobilis pdc under control of two different promoters, namely nrsRS-PnrsB and corR-PcorRT. Here, nrsRS-PnrsB was incorporated to provide the Ni inducible and corR-PcorRT was incorporated to provide the Co inducible promoter. The plasmids differed only in the incorporation of optimized ribosomal binding sites (RBS) in some of the promoters, upstream of the Zymomonas mobilis and/or Zymobacter palmae pdc, which are highlighted in the Figures and sequence denominations with an asterisk (*). The specific modifications of the RBS were incorporated by primer design, i.e. reverse primers PcorT*-EcoRI-rev (SEQ ID NO:53) and PnrsB*-EcoRI-rev (SEQ ID NO:54). The presence of the respective three different promoter-pdc versions in the corresponding Synechococcus sp. PCC 7002 hybrid strains, i.e. a first pdc production gene integrated into pAQ4 and two further pdc production genes on the respective pVZ vector, was verified by specific PCR. The transformants were then tested for EtOH production and promoter specificity under defined induction conditions in GC online measurements. The results demonstrate the hybrid strain Synechococcus sp. PCC 7002 TK115 responded specifically to Zn and produced EtOH (FIG. 14B). It was also shown that the corR-PcorT promoter in Synechococcus sp. PCC 7002 with plasmid #1217 (FIG. 15A) responds specifically to Co without any activation by Zn or Ni (FIG. 15B). In addition, tests with Synechococcus sp. PCC 7002 transformed with the self-replicating pVZ plasmid #1356 (FIG. 16A) showed that the nrsRS-PnrsB* promoter controlling the zmPDC gene responded specifically to Ni without detectable activation by Zn (FIG. 16B). However, a cross-induction of the nrsRS-PnrsB* promoter by Co was observed. To circumvent a corresponding problem of cross-induction during a production cultivation, a production gene transcriptionally controlled by the Ni-inducible promoter nrsRS-PnrsB would have to be induced first, i.e. prior to a production gene transcriptionally controlled by the Co-inducible promoter corR-PcorT. By doing that, the observed cross-induction would not be of relevance for the sequential induction of the production genes. The results further demonstrate the required monospecifity of Zn and Ni, and, with certain limitations, also of Co for induction of smtB-PsmtA, nrsRS-PnrsB and corR-PcorT in the transformants Synechococcus sp. PCC 7002 TK115 #1375, Synechococcus sp. PCC 7002 TK115 #1376, Synechococcus sp. PCC 7002 TK115 #1381 and Synechococcus sp. PCC 7002 TK115 #1383, i.e. in these transformants Zn selectively induces smtB-PsmtA, Ni selectively induces nrsRS-PnrsB and Co selectively induces corR-PcorT but the least with slight cross-induction of nrsRS-PnrsB.
In addition, the pVZ325a based construct #1460 (FIG. 31, SEQ ID NO:68) comprising the Pdc gene from Zymomonas mobilis under control of a further nickel-inducible promoter was tested in Synechococcus sp. PCC7002. The promoter PnrsB(ABCC916) was identified in the genome of a Synechococcus species that is closely related to Synechococcus PCC7002. Construct #1460 also comprises the Ni2+ dependent regulator genes nrsR and nrsS from said Synechococcus species, whose gene products act as transcriptional regulators of the nickel-inducible nrsB promoter. FIG. 31B shows the corresponding test of ethanol production of Synechococcus PCC7002 hybrid strain #1460 determined by GC online measurement under selective induction conditions. Addition of 2 μM nickel (crosshair markers) specifically induces ethanol production in PCC7002 hybrid strain #1460, whereas no significant ethanol production is observed in samples with 5 μM zinc (square markers), 5 μM cobalt (triangle markers) and with no metal-ions added (diamond markers), respectively. Notably, cobalt addition did not interfere with the action of the PnrsB(ABCC916) promoter from Synechococcus. Thus the nrsRS-PnrsB(ABCC916) promoter system derived from the Synechococcus species is a particular advantageous Ni2+ inducible promoter when used for the purpose of sequential induction of multiple pdc copies in Synechococcus PCC7002.
In alternative variants of metabolically enhanced Synechococcus sp. PCC 7002 harboring different combinations of multiple first production genes to those detailed above, other integrative constructs for the endogenous Synechococcus plasmids pAQ1 and pAQ3 were tested, either in combination or in place of ethanologenic pAQ4 construct TK115. The sequence of TK193, an integrative vector for pAQ3 is provided as SEQ ID NO:52. An example for an alternative Synechococcus sp. PCC 7002 transformant, carrying the pAQ4 construct TK115, the replicative pVZ vector #1391 (FIG. 19B, SEQ ID NO:51) and the pAQ3 construct TK193, is schematically shown in FIG. 22.
FIG. 36A schematically shows a further variant of metabolic enhancements in Synechococcus sp. PCC7002 hybrid strain TK115/#1470/#1473. The strain comprises three independently inducible pdc gene copies due to integration of each specific pdc cassette in one of the three different endogenous plasmids pAQ4, pAQ3 and pAQ1. The respective plasmid maps and sequences of the constructs TK115, #1470 and #1473 that were used for transformation of Synechococcus sp. PCC7002 were already detailed above. FIG. 36B shows the corresponding PCR analysis for confirmation of the presence of the three Pdc gene copies introduced into the endogenous plasmids pAQ4, pAQ3 and pAQ1 of Synechococcus sp. PCC7002 hybrid strain TK115/#1470/#1473. The expected PCR products specific for successful integration of each Pdc cassette into the respective endogenous plasmid were only obtained for the desired hybrid strain, whereas the parental strains TK115 and TK115/#1470 were found to produce only one or two positive PCR products, respectively, as expected. The expected size of the PCR product is indicated by the arrow on the left hand side of the shown picture of the DNA agarose gels. FIG. 36C shows the ethanol production in % (v/v) per culture OD observed with Synechococcus sp. PCC7002 hybrid strain TK115/#1470/#1473, as determined by GC online measurements under selective induction conditions. Data represent the average of biological duplicates. In contrast to the control GC vial with no metal-ions added (diamond markers), addition of the metal-ions Zn2+ (square markers), Co2+ (triangle markers) and Ni2+ (crosshair markers) specifically induce one of the three introduced Pdc genes, as is evident from the substantially elevated ethanol production. FIG. 36D shows the corresponding ethanol production in % (v/v) per culture OD observed with Synechococcus sp. PCC7002 hybrid strain TK115/#1470. Data represent the average of biological duplicates. In comparison to hybrid strain TK115/#1470/#1473, this strain yet lacks the pdc gene under transcriptional control of the nickel-inducible PnrsB916 promoter. The results show that in this case, in contrast to the results obtained from strain TK115/#1470/#1473 shown in FIG. 36C, the addition of Ni2+ (crosshair markers) does not induce significant ethanol production, whereas the addition of the metal-ions Zn2+ (square markers) and Co2+ (triangle markers) again specifically induces substantially elevated ethanol production. Taken together, these results demonstrate that each of the three introduced Pdc copies can be controlled specifically by the choice of added metal-ion which allows a sequential and independent induction procedure that will extent the duration of ethanol production.
As an alternative hybrid strain variant, FIG. 37A schematically shows the two genetic manipulations realised in Synechococcus sp. PCC7002 hybrid strain #1332/TK162 harbouring two independently inducible pdc gene copies by integration of two distinct pdc/adh cassettes into the endogenous plasmids pAQ4 and pAQ3, respectively. FIG. 37B shows the results from PCR analysis for confirmation of the two pdc gene copies introduced into the endogenous plasmids pAQ4 and pAQ3 of Synechococcus PCC7002. The hybrid strain #1332/TK162 exhibits the expected PCR products confirming the successful integration of both pdc cassettes into the respective endogenous plasmid, whereas the parental hybrid strain #1332 exhibits only one positive PCR product, as expected. The predicted size of the PCR product is indicated by an arrow on the left hand side of the DNA agarose gel image. FIG. 37C shows the results from ethanol production in % (v/v) per OD of Synechococcus PCC7002 hybrid strain #1332/TK162, as determined by GC online measurement under selective induction conditions. Whilst in the control sample with no metal-ions added (diamond markers) insignificant ethanol production is observed, the addition 5 μM zinc (square markers), 10 μM cobalt (triangle markers) and 20 μM cobalt (round markers) specifically induce one of both introduced pdc genes and the ethanol production is substantially elevated. This demonstrates that each pdc gene copy can be transcriptionally controlled by addition of zinc and cobalt, respectively, allowing for a sequential and independent induction procedure for an extended duration of ethanol production.
Example 13
Long-Term Cultivation of Metabolically Enhanced Synechococcus sp. PCC7002 Hybrid Strain TK115/#1470/#1473 with Sequential Induction of Multiple First Production Genes
Synechococcus sp. PCC7002 hybrid strain TK115/#1470/#1473 is grown as pre-culture in mBG11 liquid medium supplemented with kanamycin, gentamycin and streptomycin to apply selection pressure for constructs TK115, #1470 and #1473. Neither Zn, Ni or Co will be added to the culture at this stage in order to avoid diverting fixed-carbon from cell growth, but to grow the uninduced culture to a high cell density. Upscale of the pre-culture into a main culture using mBG-11 medium (35 psu, artificial seawater salts) without addition of metal ions (Zn, Ni, Co) maintains repression of the three different promoters PsmtA, PcorT* 1 and PnrsB916.
Cells will be cultivated in 0.5 L round bottles with a culture volume of 0.4 L. Mixing will be achieved with a magnetic stir bar at 250 rpm, applied continuously. For instance, a light/dark photoperiod of 12 h/12 h will be used. Illumination of the cultures will be realized by fluorescence lamps (Sylvania Grolux FHO 39W/T5/GRO). The light intensity will be dynamically adjusted according to the cell density, for instance increasing from 140 μE m−2 s−1 to up to 450 μE m−2 s−1, whilst illumination may be provided from two sides of the culture vessels. The temperature regime may be set to 25-28° C. during the dark phase and 36-39° C. during the light phase. CO2 enriched air may be bubbled through the cultures by injection of 0.5% CO2 at a flow rate of 20 mL min−1.
At first, the cells may be induced by zinc addition. For this purpose, 5 μM zinc sulfate may be added to the culture on the first cultivation day, and further 5 μM zinc sulfate on the second cultivation day, to give 10 μM zinc sulphate in total. Thenceforth the productivity of the culture will be monitored. After a few weeks weeks, a stagnation or decline of the cell density and/or ethanol productivity may be detected. Hereupon, a medium exchange can be performed, for instance by spinning the culture down at 6500 rpm for 10 minutes and replacing the supernatant using fresh mBG-11 medium, thereby adjusting the cell density to an OD750nm of about 1. A recovery phase of about one week may be maintained under repressed conditions, i.e. without addition of Zn, Co or Ni. Alternatively, the medium exchange and recovery phase may be omitted by directly entering the next induction step. Afterwards, the second induction may then realized by addition of 5 μM cobalt sulphate. After several weeks of cultivation under induced conditions, a stagnation or decline of the cell density and/or ethanol productivity may again be detected which may again be followed by a medium exchange as outlined above, and one week cultivation under repressed condition for culture recovery. Alternatively, the medium exchange and recovery phase may again be omitted by directly entering the next induction step. Finally, the third induction may subsequently be accomplished with addition of 2 μM nickel sulfate. Accordingly, a third ethanol production phase may be observed, until after several weeks further cultivation time a stagnation or decline of the cell density and/or ethanol productivity may again be detected and the experiment may be terminated.
In summary, the serial induction of the three inducible promoters controlling the recombinant first production genes in Synechococcus sp. PCC7002 hybrid strain TK115/#1470/#1473 may allow to significantly prolong the production period with the metabolically enhanced cyanobacterium set forth by the present invention when compared to a hybrid strain harbouring only one production gene.
Example 14
Generation of Metabolically Enhanced Synechococcus sp. PCC 7002 Strains with Multiple First Production Genes Under the Transcriptional Control of Different Promoters which Require Different Concentrations of the Same Inducing Agent for Induction
Synechococcus sp. PCC 7002 was transformed with constructs TK115 and #1480 to generate and test a metabolically enhanced cyanobacterium harboring two first production genes under the transcriptional control of different inducible promoters, as well as a second production gene under the transcriptional control of a constitutive promoter. In this example, the promoters controlling the two first production genes are chosen to be both inducible by zinc, but require different concentrations of zinc for full induction.
FIG. 38B is a schematic illustration of the two genetic manipulations realised in Synechococcus sp. PCC7002 hybrid strain #TK115/#1480, harbouring two inducible pdc gene copies both controlled by zinc inducible promoters smtB-PsmtA and aztR-PaztA, respectively, integrated into the endogenous plasmids pAQ4 and pAQ3.
FIG. 38C shows the corresponding results from PCR analysis for confirmation of the presence of the two pdc gene copies introduced in the endogenous plasmids pAQ4 and pAQ3 of Synechococcus PCC7002. The hybrid strain TK115/#1480 exhibits the expected PCR products which specifically confirm the successful integration of both pdc cassettes into the respective endogenous plasmid, whereas the parental hybrid strain TK115 exhibits only one positive PCR product, as expected. The predicted size of the expected PCR product is indicated by an arrow on the left hand side of the shown picture of the DNA agarose gel images.
FIG. 38D shows the results of the corresponding ethanol production achieved with Synechococcus sp. PCC7002 hybrid strain TK115/#1480 compared to the strains TK115 and #1480 harbouring a single pdc gene only, as determined by GC online measurement using a zinc concentration of 5 μM for induction. Data represent the arithmetic mean of biological duplicates. At 5 μM Zn2+ addition, which leads to a moderate induction of smtB-PsmtA as well as the aztR-PaztA promoter system in Synechococcus PCC7002 the hybrid strain TK1151#1480 (triangle markers) exhibits a substantial higher ethanol production of approximately 0.0109% (v/v) per OD and day compared to both parental strains TK115 (triangle markers) and #1480 (square markers) harbouring only one pdc copy, which produce only 0.0077% and 0.0054% (v/v) per OD and day, respectively. This corresponds to approximately 200% higher ethanol production with hybrid strain TK115/#1480 in comparison to hybrid strain #1480, and approximately 142% higher ethanol production in comparison to hybrid strain TK115 at 5 μM Zn2+ addition. This finding is attributed to the elevated gene dosage realized by integration of two different pdc gene copies into pAQ4 and pAQ3.
FIG. 38E shows the corresponding results from ethanol production when 10 μM Zn2+ were used for induction of the promoters. It can be derived that under these inducing conditions hybrid strain TK115 exhibits an increased ethanol production compared to induction with 5 μM zinc. The ethanol production of TK115 is very similar to TK115/#1480. In contrast, only a minor increase in the ethanol production rate is observed for #1480 at 10 μM zinc induction.
The results demonstrate that the hybrid strain TK115/#1480 allows accomplishing a high ethanol production already at a moderate induction condition, e.g. 5 μM zinc, and that the ethanol production can be further increased by higher zinc concentrations, because the promoter PsmtA sustains a higher zinc concentration for full induction than the PaztA promoter.
This example illustrates how a metabolically enhanced cyanobacterium with multiple first production genes under control of inducible promoters requiring different concentrations of the same inducing agent can be used inventively for long-term ethanol production to accomplish an essentially constant level of ethanol production. For instance, two first production genes under the transcriptional control of inducible promoters which are inducible by the same inducing agent but require different concentrations of inducing agent for full induction, may be present in the cyanobacterium. During ethanol production, at first a low concentration of inducing agent may be established, leading to high expression of the first production gene under the transcriptional control of the inducible promoter requiring a low inducing agent concentration, whereas the other first production gene under the transcriptional control of the inducible promoter requiring a higher inducing agent concentration may be not expressed or only slightly expressed. Thus, the genetic selection pressure on the latter first production gene is kept low. When, for instance, stagnation or decrease in productivity is observed, for example due to the functional loss of some of the highly expressed first production genes by a “loss of function” mutation, a higher concentration of inducing agent may be added in order to increase the expression level of the first production gene under the transcriptional control of the inducible promoter requiring the higher inducing agent concentration. In this way, the functional loss of first production genes under transcriptional control of the promoter requiring a lower inducing concentration for full induction can be compensated, and the ethanol production can be maintained over a longer period of time by subsequent full induction of the remaining functional pdc gene copy under control of the promoter requiring the higher inducing concentration. Consequently, the ethanol production can be significantly prolonged in comparison to ethanol production with a conventional cyanobacterium harbouring only one first production gene.
As an alternative to the use of different promoters as above, also variants of the same promoter may be used, wherein these variants are engineered so as to require different concentrations of the same inducing agent for induction. As an example, Synechococcus sp. PCC 7002 may be transformed with constructs TK162 and a modified version of #1233, hereinafter named #1233*, to generate and test a metabolically enhanced cyanobacterium harboring two first production genes under the transcriptional control of modified variants of the same inducible promoter based on the smtB-PsmtA promoter, as well as a second production gene under the transcriptional control of a constitutive promoter. First, Synechococcus sp. PCC 7002 may be transformed with the integrative construct TK162 via natural DNA uptake as described before. The plasmid map is shown in FIG. 24, and the nucleotide sequence is deposited as SEQ ID NO:65. By homologous recombination with the endogenous plasmid pAQ3 the transformant Synechococcus sp. PCC 7002 strain TK162 containing the ethanologenic gene cassette under control of the zinc-inducible smtB-PsmtA promoter may be generated. After checking for correct replacement of the wild type version against the hybrid version and full segregation of the transformants by a specific polymerase chain reaction, the integrative plasmid #1233* may be introduced into the ethanologenic Synechococcus sp. PCC 7002 strain TK162 by natural uptake as described before. The plasmid #1233* may comprise a different pdc copy than TK162, namely the pdc from Zymobacter palmae while TK162 contains the pdc from Zymomonas mobilis. In contrast to the original plasmid #1233, the plasmid #1233* may comprise a modified variant of the smtB-PsmtA promoter (smtB-PsmtA*) in control of the pdc-encoding gene. Such a variant of the smtB-PsmtA promoter may comprise base pair substitutions and/or deletions in the operator region, the TATA box and/or ribosome binding sites, respectively, of PsmtA, which change the Zn concentration required for induction of the promoter smtB-PsmtA* compared to its wild-type version. Accordingly, the expression of the pdc from Zymobacter palmae on the variant of #1233* may require a different concentration of the inductor Zn2+ than the expression of the pdc from Zymomonas mobilis on TK162 controlled by the unmodified smtB-PsmtA promoter.
A third and fourth pdc version under control of smtB-PsmtA promoter variants may be introduced on a replicative pVZ version, such as vector #1375 shown in FIG. 17A, after the promoters nrsRS-PnrsB and/or corR-PcorT* have been replaced by further promoter variants smtB-PsmtA** and smtB-PsmtA*** variants which may again differ from each other as well as from smtB-PsmtA* and the wild type promoter with respect to the Zn concentration required for induction.
Alternatively to variants of the smtB-PsmtA promoter other Zn inducible promoters, such as ziaR-PziaA (from Synechocystis sp. PCC6803) in combination with aztR-PaztA (from Anabaena sp. PCC7120) in combination with smtB-PsmtA, respectively, may be used to drive sequentially different pdc genes by increasing the concentration of the same inducing agent.
Furthermore, alternatively to the Zn inducible smtB-PsmtA promoter, other metal ion inducible promoters, such as corR-PcorT in combination with correspondingly modified variants, and/or nrsRS-PnrsB in combination with correspondingly modified variants, may be used inventively to selectively drive the expression of the corresponding different pdc genes by increasing the concentration of the same metal-ion inductor.
Example 15
Long-Term Cultivation of Metabolically Enhanced Synechococcus sp. PCC 7002 Strain TK162/#1233* with Sequential Induction of Multiple First Production Genes Under the Transcriptional Control of Variants of the Same Promoter Requiring Different Concentrations of the Same Inducing Agent for Induction
Synechococcus sp. PCC 7002 strain TK162/#1233* can be grown as a pre-culture in mBG11 liquid medium supplemented with kanamycin and streptomycin to apply selection pressure for constructs TK162 and #1233*. Zn is not added to the culture at this stage in order to avoid diverting fixed-carbon from cell growth, but to grow the uninduced culture to a high cell density. Upscale of the pre-culture into a main culture without addition of metal Zn, maintains repression of the smtB-PsmtA promoters driving the two pdc genes present on TK162 and #1233*. Here, 100 ml pre-culture can be used to inoculate the main culture in 500 ml Crison-PBRS. Upon reaching an OD750nm value of approximately 2, the culture may be induced with 5 μM Zn, leading to expression of the ethanologenic genes with Zymomonas mobilis pdc on the endogenous plasmid pAQ3 (TK162). Using 5 μM Zn2+ the modified variant of the PsmtA promoter (smtB-PsmtA*) present on #1233* may remain essentially uninduced. Induction of smtB-PsmtA on TK162 leads to the production of ethanol Thenceforth the productivity of the culture may be monitored. After a time period which may be several weeks or a few months, a decline of the productivity and the pdc enzyme activity may be detected. Hereupon the Zymobacter palmae pdc gene present on #1233* may be induced by addition of additional 5-10 μM Zn2+ leading to expression of this second pdc gene and the recovery of ethanol productivity in the culture before the culture may later become unproductive.
In summary, the serial induction of the inducible promoters controlling the recombinant first production genes can allow to significantly prolong the production period with the metabolically enhanced cyanobacterium set forth by the present invention compared to a conventional hybrid strain.
If the modified construct #1375 with the ethanologenic genes under control of smtB-PsmtA** and smtB-PsmtA*** is also present in the strain to form Synechococcus sp. PCC 7002 strain TK162/#1233*/1375*, the production phase can be further extended by a third and further fourth selective induction of the expression of the corresponding third and fourth pdc gene using the required further increased Zn2+ concentrations.
Example 16
Generation of Metabolically Enhanced Synechococcus sp. PCC 7002 Strain with Multiple First Production Genes Under the Transcriptional Control of the Same Gradually Inducible Promoter
Synechococcus sp. PCC7002 hybrid strain #1563/#1568/#1692 was generated by sequentially introducing three zinc-inducible pdc gene copies controlled by the smtB-PsmtA promoter into different locations of the Synechococcus PCC7002 chromosome as shown in FIG. 40A. For this purpose, the construct #1563 was used for integration of a first pdc gene from Zymomonas mobilis and an adh gene from Synechocystis sp. PCC6803 in between gene loci A0124 and A0125 (integration site A), construct #1568 was used for integration of a degenerated second pdc gene from Zymomonas mobilis and an adh gene from Synechocystis sp. PCC6803 in between gene loci 1330 and 1331 (integration site B), and construct #1692 was used for integration of a third pdc gene from Zymomonas mobilis and an adh gene from Synechocystis sp. PCC6803 in between gene loci A2578 and A2579 (integration site C). The successful integration of the three zinc-inducible pdc gene copies and the adh genes in the three different locations of the Synechococcus PCC7002 chromosome was verified by PCR analysis (FIG. 40B). PCR analysis of Synechococcus PCC7002 #1563/#1568/#1692 yielded all three expected PCR products specific for successful integration of each pdc/adh cassette into the different locations of the chromosome, whereas the parental precursor strains #1563 and #1563/#1568 yielded only one or two positive PCR product respectively, as was expected. The predicted product size of the PCR amplificate is indicated by an arrow on the left hand side of the DNA agarose gel images. Afterwards, the ethanol production with the metabolically enhanced hybrid strain Synechococcus sp. PCC7002 #1563/#1568/#1692 (FIG. 40F) was compared with the ethanol production of the precursor strains #1563 (FIG. 40C), #1568 (FIG. 40D) and #1563/#1568 FIG. 40F) harbouring a single pdc gene or two pdc genes only, respectively, by GC online measurement at a zinc concentrations of 0, 5 and 10 μM. Data represent arithmetic mean of biological duplicates for each data point in the graphs. The metabolically enhanced hybrid strain #1563/#1568/#1692 exhibits at both zinc induction concentrations of 5 μM and 10 μM a substantially higher ethanol production compared to the precursor strains with only one pdc gene. The production rate is approximately 171% higher compared to strain #1563, and approximately 239% higher compared to #1568. In addition, still an approximately 112% higher ethanol production rate is observed with hybrid strain #1563/#1568/#1692 in comparison to the precursor strain #1563/41568 with two pdc genes at both zinc induction concentrations of 5 μM and 10 μM. These results are attributed to the elevated gene dosage realized by integration of three pdc gene copies into different locations of the chromosome.
Taken together, these results clearly show that the smtB-PsmtA promoter can be gradually induced by increasing the zinc-concentration and to correspondingly gradually increase the expression level of the PsmtA-controlled pdc genes, whilst at the same time achieving a relatively high ethanol production rate already at low inducing concentrations due to the elevated pdc gene copy number in the metabolically enhanced cyanobacterium.
As a second variant, a Synechococcus sp. PCC7002 hybrid strain #1564/#16331#1574 was generated by sequentially introducing three cobalt-inducible pdc gene copies controlled by the corR-PcorT promoter into different locations of the Synechococcus PCC7002 chromosome as shown in FIG. 42A. For this purpose, the construct #1564 was used for integration of a first pdc gene from Zymomonas mobilis and an adh gene from Synechocystis sp. PCC6803 in between gene loci A0124 and A0125 (integration site A), construct #1633 was used for integration of a degenerated second pdc gene from Zymomonas mobilis and an adh gene from Synechocystis sp. PCC6803 in between gene loci 1330 and 1331 (integration site B), and construct #1574 was used for integration of a third pdc gene from Zymomobacter palmae and an adh gene from Synechocystis sp. PCC6803 in between gene loci A2578 and A2579 (integration site C). The successful integration of the three cobalt-inducible pdc gene copies and the adh genes in the three different locations of the Synechococcus PCC7002 chromosome was verified by PCR analysis (FIG. 42B). PCR analysis of Synechococcus PCC7002 #1564/#1633/#1574 yielded all three expected PCR products specific for successful integration of each pdc/adh cassette into the different locations of the chromosome, whereas the parental precursor strains #1564 and #1564/#1633 yielded only one or two positive PCR product respectively, as was expected. The predicted product size of the PCR amplificate is indicated by an arrow on the left hand side of the DNA agarose gel images.
Next, the ethanol production with the metabolically enhanced hybrid strain Synechococcus sp. PCC7002 #1564/#1633/#1574 will compared with the ethanol production of the precursor strains #1564, #1633 and #1564/#1633 harbouring a single pdc gene and two pdc genes only, respectively, by GC online measurement at cobalt concentrations of 0, 5 and 10 The metabolically enhanced hybrid strain #1564/#1633/#1574 with the three pdc genes may exhibit a higher ethanol production compared to precursor strain #1564, #1633 and #1564/#1633 with one or two pdc gene copies only. This result may be attributed to the elevated gene dosage realized by integration of three pdc gene copies into different locations of the chromosome. These results will demonstrate that also the corR-PcorT promoter can be gradually induced by increasing the cobalt-concentration and to correspondingly gradually increase the expression level of the PcorT-controlled pdc genes, whilst at the same time achieving a relatively high ethanol production rate already at low inducing concentrations due to the elevated pdc gene copy number in the metabolically enhanced cyanobacterium.
In a further variant, Synechococcus sp. PCC 7002 can be transformed with constructs TK162 and #1233 to generate and test a metabolically enhanced cyanobacterium harboring two first production genes under the transcriptional control of the same inducible promoter, namely the Zn-inducible promoter smtB-PsmtA, and a second production gene under the transcriptional control of a constitutive promoter. First, Synechococcus sp. PCC 7002 can be transformed with the integrative construct TK162 (pGEM-AQ3::smtB-PsmtA-zmPDC-PrbcL-synADHdeg) via natural DNA uptake as described above. The plasmid map is shown in FIG. 24, and the nucleotide sequence is deposited as SEQ ID NO:65. By homologous recombination with the endogenous plasmid pAQ3 the transformant Synechococcus sp. PCC 7002 strain TK162 containing the ethanologenic gene cassette under control of the zinc-inducible smtB-PsmtA promoter is generated (pAQ3::smtB-PsmtA-zmPDC-PrbcL-synADHdeg). After checking for correct replacement of the wild type version against the hybrid version and full segregation of the transformants by a specific polymerase chain reaction, the integrative plasmid #1233 (pGEM-AQ4::smtB-PsmtA-zpPDC-PrbcL-synADHdeg.) can be introduced into the ethanologenic transformant strain TK162 by natural uptake as described previously. The plasmid #1233 comprises a different pdc copy than TK162, namely the pdc from Zymobacter palmae while TK162 contains the pdc from Zymomonas mobilis. By homologous recombination with the endogenous plasmid pAQ4 the transformant strain TK162/#1233 (pAQ3::smtB-zmPDC-PrbcL-synADHdeg, pAQ4::smtB-PsmtA-zpPDC-PrbcL-synADHdeg) is generated. Selection of transformant TK162 occurs via Sm/St and selection of TK162/#1233 via Km/Nm. The map of plasmid #1233 is shown in FIG. 25, the corresponding DNA sequence is provided as SEQ ID NO:66. The presence of both different pdc constructs in the transformant can be verified by PCR.
A third and fourth pdc version under control of smtB-PsmtA can be further introduced into hybrid strain TK162/#1233 on a self-replicative pVZ plasmid, such as plasmid #1375 shown in figure FIG. 17A, after the nrsRS-PnrsB and/or corR-PcorT* of #1375 have been replaced by smtB-PsmtA, to produce the Synechococcus sp. PCC 7002 strain TK162/#1233/#1375*. The selection of respective transformants can occur via Gentamycin resistance. Moreover, as alternative to the Zn-inducible smtB-PsmtA promoter of TK162/#1233 or TK162/#1233/#1375*, respectively, other metal ion inducible promoters, such as corR-PcorT or nrsRS-PnrsB can be also used to drive different pdc genes in a dose-dependent manner by increasing the concentration of corresponding inductor metal in subsequent method steps. Preferably, the different pdc genes are located on different genetic elements.
Example 17
Long-Term Cultivation of Metabolically Enhanced Synechococcus sp. PCC 7002 Hybrid Strains #1563/#1568/#1692 or #1564/#1633/#1574 with Sequential Gradual Induction of Multiple First Production Genes
Synechococcus sp. PCC 7002 #1563/#1568/#1692 or #1564/#1633/#1574 are grown as a pre-culture in mBG11 liquid medium supplemented with Sp, Gm and Km to apply selection pressure for constructs #1563, #1568 and #1692, or #1564, #1633 and #1574, respectively. Zn/Co are not added to the cultures at this stage in order to avoid diverting fixed-carbon from cell growth, but to grow the uninduced culture to a high cell density. Upscale of the #1563/#1568/#1692 pre-culture into a main culture without addition of metals Zn maintains repression of the smtB-PsmtA promoter driving the pdc genes present on #1563, #1568 and #1692, whereas the #1564/#1633/#1574 main culture without addition of Co likewise maintains repression of the corR-PcorT promoter driving the pdc genes present on #1564, #1633, #1574. Here, 100 ml pre-culture can be used to inoculate the main culture in 500 ml Crison-PBRs. Upon reaching an OD750nm value of approximately 2, the #1563/#1568/#1692 culture can be induced with 2.5-5 μM Zn2+, leading to dose-dependent expression of the pdc genes under control of the smtB-PsmtA promoter. In similar manner, the #1564/#1633/#1574 culture can be induced with 2.5-5 μM Co2+, leading to dose-dependent expression of the pdc genes under control of the corR-PcorT promoter. For both strains, due to the increased number of pdc genes under the transcriptional control of the same promoter, a relatively high ethanol production rate can be expected already at a low induction conditions, e.g. 2.5 μM zinc or 2.5 μM cobalt, respectively. After a time period which may be several weeks or a few months, a decline of the productivity and the pdc enzyme activity may be detected. Hereupon, the dose of the inductor Zn2+ or Co2+ may be increased to 5-10 μM to increase induction of the smtB-PsmtA or corR-PcorT promoter. This will cause elevated transcription of the pdc genes and lead to the recovery of pdc enzyme activity and ethanol productivity in the cultures. After another time period which may be several weeks or a few months, another decline of the productivity and the pdc enzyme activity may be detected. In this case, the production phase can be further extended by a third dose-dependent induction, which may occur at 10-15 μM Zn2+ or Co2+, respectively, to further increase induction of the smtB-PsmtA or corR-PcorT promoter.
In summary, the dose-dependent gradual induction of the smtB-PsmtA promoter by different levels of Zn2+, e.g. a moderate prior to a complete induction, allows to significantly prolong the production period of the first chemical compound with the metabolically enhanced cyanobacterium set forth by the present invention compared to a conventional hybrid strain. The same principle applies to the dose-dependent gradual induction of the corR-PcorT promoter by different levels of Co2+.
In this manner, metabolically enhanced cyanobacterial hybrid strains with multiple first production genes under the transcriptional control of the same gradually inducible promoter can be used inventively by stepwisely increasing induction of the promoters to compensate the loss of functional pdc genes, which may for instance happen due to occurrence of a “loss of function” mutation. Thereby ethanol production can be sustained at the same level by appropriate addition of inducing agent, for instance up to 15 μM zinc or 20 μM cobalt, when the number of remaining functional pdc copies is noticeably decreasing. By applying this strategy ethanol production can be maintained over a longer period of time compared to a conventional ethanologenic cell line with only one single pdc gene copy.
Example 18
Long-Term Cultivation of Metabolically Enhanced Synechococcus sp. PCC7002 Hybrid Strains TK162/#1233 with Sequential Gradual Induction of Multiple First Production Genes
Synechococcus sp. PCC 7002 strain TK162/#1233 is grown as a pre-culture in mBG11 liquid medium supplemented with kanamycin and streptomycin to apply selection pressure for constructs TK162 and #1233. Zn is not added to the culture at this stage in order to avoid diverting fixed-carbon from cell growth, but to grow the uninduced culture to a high cell density. Upscale of the pre-culture into a main culture without addition of Zn maintains repression of the smtB-PsmtA promoter driving the two pdc genes present on #1233 and TK162. Here, 100 ml pre-culture may be used to inoculate the main culture in 500 ml Crison-PBRS. Upon reaching an OD750nm value of approximately 2, the culture may be induced with 2.5-5 μM Zn2+, leading to dose-dependent expression of the ethanologenic genes encoding the Zymomonas mobilis and Zymobacter palmae pdc under control of the smtB-PsmtA promoter on construct TK162 and #1233, and to the production of ethanol Thenceforth the productivity of the culture may be monitored. After a time period which may be several weeks or a few months, a decline of the productivity and the pdc enzyme activity may be detected. Hereupon the dose of the inductor Zn2+ may be increased to 10 μM to fully induce the smtB-PsmtA promoter. This may cause full transcription of the pdc genes and lead to the recovery of pdc enzyme activity and ethanol productivity in the culture before the culture may become unproductive. In summary, the dose-dependent gradual induction of the smtB-PsmtA promoter by different levels of Zn2+, e.g. a moderate prior to a complete induction, can allow to significantly prolong the production period of the first chemical compound with the metabolically enhanced cyanobacterium set forth by the present invention compared to a conventional hybrid strain.
If the modified construct #1375* harboring the ethanologenic genes under control of the smtB-PsmtA promoter is also present in Synechococcus sp. PCC 7002 strain TK162/#1233/#1375*, production phase can be further extended by a third method step for gradual induction of the promoter. For example, the first dose-dependent induction may occur at 3.3 μM Zn2+, the second dose-dependent induction may occur at 6.6 μM Zn2++ and the third dose-dependent induction may occur at 10 μM Zn2+.
REFERENCE NUMERAL
CB: Cyanobacterial cell
CH: Bacterial chromosome
EP: Endogenous plasmid
VC1: Self-replicating plasmid vector with first production gene under the transcriptional control of a first inducible promoter for the first production gene
MT1: Mutation in first production gene
CH2: Bacterial chromosome with second first production gene under the transcriptional control of a second inducible promoter for the first production gene
EP3: Endogenous plasmid with third first production gene under the transcriptional control of a third inducible promoter for the first production gene
MT2: Mutation in the second first production gene
VC123: Self-replicating plasmid vector with a first production gene under the transcriptional control of a first inducible promoter for the first production gene, a second first production gene under the transcriptional control of a second inducible promoter for the first production gene, and a third first production gene under the transcriptional control of a third inducible promoter for the first production gene

## Claims

1. A method for producing ethanol from a photoautotrophic cyanobacterium modified to produce ethanol, comprising:
A) culturing the photoautotrophic cyanobacterium comprising:
i) at least one recombinant alcohol dehydrogenase gene;
ii) a first recombinant pyruvate decarboxylase gene under the control of a first inducible promoter; and
iii) a second recombinant pyruvate decarboxylase gene under the control of a second inducible promoter;

under conditions for induction of the first inducible promoter, wherein the photoautotrophic cyanobacterium produces ethanol; and
B) culturing the photoautotrophic cyanobacterium under conditions for induction of the second inducible promoter, wherein the photoautotrophic cyanobacterium produces ethanol;
further wherein method step A) and method step B) are temporally separated, further wherein the second inducible promoter is maintained in a substantially uninduced state during method step A).

2. The method of claim 1, wherein the recombinant alcohol dehydrogenase genes are operably linked to the recombinant pyruvate decarboxylase genes to form functional operons.

3. The method of claim 2, wherein said first and second inducible promoters are selected from the group consisting of PntcA, PnbIA, PisiA, PpetJ, PpetE, PggpS, PpsbA2, PpsaA, PsigB, PIrtA, PhtpG, PnirA, PnarB, PnrtA, PhspA, PclpB1, PhliB, PcrhC, ziaR-PziaA, smtB-PsmtA, corR-PcorT, nrsRS-PnrsB, nrsRS-PnrsB916, aztR-PaztA, bxmR-PbmtA, bxaR-Pbxal, zntR-PzntA, czrR-PczrB, and nmtR-PnmtA.

4. The method of claim 2, wherein the first and second promoters are selected from the group consisting of zirR-PziaA, smtB-PsmtA, corR-PcorT, aztR-PaztA, and nrsRS-PnrsB.

5. The method of claim 3, wherein the first and second promoters are responsive to nitrate concentration and/or ammonium concentration.

6. The method of claim 2, wherein at least some of the recombinant alcohol dehydrogenase genes and/or recombinant pyruvate decarboxylase genes are located on at least one extrachromosomal plasmid.

7. The method of claim 6, wherein at least some of the recombinant alcohol dehydrogenase genes and/or recombinant pyruvate decarboxylase genes are located on two or more extrachromosomal plasmids wherein said plasmids have different copy numbers.

8. The method of claim 1, wherein at least one alcohol dehydrogenase gene is under the transcriptional control of a different promoter than the first and second pyruvate decarboxylase genes.

9. The method of claim 8, wherein at least one alcohol dehydrogenase gene is under the control of a constitutive promoter.

10. The method of claim 1, wherein the first and second inducible promoters are inducible by different concentrations of a first inducing agent.

11. The method of claim 10, wherein the first and second inducible promoters are zinc-inducible promoters.

12. The method of claim 11, wherein the zinc-inducible promoters are aztR-PaztA and smtB-PsmtA.

13. The method of claim 10, wherein the first and second inducible promoters are nucleic acid sequence variants of the same promoter.

14. The method of claim 13, wherein the first and second inducible promoters have a sequence identity of at least 90%.

15. The method of claim 14, wherein the first inducible promoter is smtB-PsmtA, and the second inducible promoter is a gene modification of smtB-PsmtA.

16. A method for producing ethanol from a photoautotrophic cyanobacterium modified to produce ethanol, comprising:
A) culturing the photoautotrophic cyanobacterium comprising at least two ethanologenic gene cassettes located at different locations in the genome, comprising a recombinant alcohol dehydrogenase gene and a recombinant pyruvate decarboxylase gene, wherein the promoters regulating the pyruvate decarboxylase gene of the at least two ethanologenic gene cassettes are identical, gradually-inducible promoters, under conditions for a low level of promoter induction, wherein the photoautotrophic cyanobacterium produces ethanol for several weeks;
B) thereafter, after either ethanol productivity or pyruvate decarboxylase enzyme activity declines, culturing the photoautotrophic cyanobacterium under conditions for a higher level of promoter induction than in step A), wherein the photoautotrophic cyanobacterium continues to produce ethanol, wherein ethanol production in the culture is maintained for a longer period of time than with step A) alone.

17. The method of claim 16, wherein the gradually-inducible promoter is inducible by zinc.

18. The method of claim 17, wherein the gradually-inducible promoter is smtB-PsmtA.

19. The method of claim 16, wherein the gradually-inducible promoter is inducible by cobalt.

20. The method of claim 19, wherein the gradually-inducible promoter is corR-PcorT.