Photoautotrophic Growth Rate Enhancement of Synechocystis sp. PCC6803 by Heterologous Production of 2-Oxoglutarate:Ferredoxin Oxidoreductase from Chlorobaculum tepidum.

2-Oxoglutarate:ferredoxin oxidoreductase from Chlorobaculum tepidum (CtOGOR) is a carbon-fixing enzyme in the reductive TCA cycle that reversibly carboxylates succinyl-CoA to yield 2-oxoglutarate. CtOGOR is a heterotetramer of two large (α = 68 kDa) and two small (β = 38 kDa) subunits. The αβ protomer harbors one thiamine pyrophosphate and two 4Fe-4S clusters. Nonetheless, the enzyme has a considerable oxygen tolerance with a half-life of 143 min at 215 μM dissolved oxygen. Kinetic analyses of the purified recombinant CtOGOR revealed a lower Km for succinyl-CoA than for 2-oxoglutarate. Cellular levels of 2-oxoglutarate and glutamate—a product of glutamine oxoglutarate aminotransferase and glutamate dehydrogenase—increased more than twofold in the exponential phase compared with the control strain, leading to an approximately >30% increase in the photoautotrophic growth rate. Thus, CtOGOR was successfully produced in Synechocystis, thereby boosting carboxylation, resulting in enhanced photoautotrophic growth.