Genetically Enhanced Cyanobacteria Lacking Functional Genes Conferring Biocide Resistance for the Production of Chemical Compounds

A genetically enhanced cyanobacterium producing ethanol, comprising:

• a) a genetically enhanced genome with a first gene inactivation in a first conditionally essential gene of the cyanobacterium;
• wherein the first conditionally essential gene is selected from the group consisting of narB, ziaA, smtA, corT, and combinations thereof;
• and
• b) a first extrachromosomal plasmid harboring the first essential or conditionally essential gene and at least one first production gene for the production of ethanol;
• wherein the cyanobacterium lacks a functional gene conferring biocide resistance.

A genetically enhanced cyanobacterium producing ethanol, comprising:

• a) a genetically enhanced genome with a first gene inactivation in a first essential or conditionally essential gene of the cyanobacterium;
• and
• b) a first extrachromosomal plasmid harboring the first essential or conditionally essential gene and at least one first production gene coding for Pdc enzyme and a second production gene coding for Adh enzyme, wherein a transcription terminator sequence is present between the first and second production gene and wherein the first production gene is controlled by an inducible promoter and the second production gene is under the transcriptional control of a constitutive promoter;
• wherein the cyanobacterium lacks a functional gene conferring biocide resistance.

A method for producing ethanol, comprising the method steps of:

• a) obtaining a genetically enhanced cyanobacterium producing ethanol, comprising
• i) a genetically enhanced genome with a first gene inactivation in a first essential or conditionally essential gene of the cyanobacterium selected from the group consisting of smtAB, leuB, ziaRA, corRT, narB and pyrF;
• and
• ii) a first extrachromosomal plasmid harboring the first essential or conditionally essential gene and at least one first production gene for the production of ethanol, wherein the at least one first production gene for the production of ethanol encodes an enzyme selected from the group consisting of Adh, Pdc, AdhE and combinations thereof;
• wherein the cyanobacterium lacks a functional gene conferring biocide resistance, further wherein the genome harbors more than one copy of the first essential or conditionally essential gene and wherein all copies of the first essential gene carry at least one gene inactivation;
• b) culturing said genetically enhanced cyanobacterium in the absence of a biocide, the cyanobacterium producing ethanol;
• and
• c) recovering the ethanol.