Engineered cyanobacteria with additional overexpression of selected Calvin-Benson-Bassham enzymes show further increased ethanol production

Cyanobacteria are one of the most promising microorganisms to produce biofuels and renewable chemicals due to their oxygenic autotrophic growth properties. However, to rely on photosynthesis, which is one of the main reasons for slow growth, low carbon assimlation rate and low production, is a bottleneck. To address this challenge, optimizing the Calvin-Benson-Bassham (CBB) cycle is one of the strategies since it is the main carbon fixation pathway. In a previous study, we showed that overexpression of either aldolase (FBA), transketolase (TK), or fructose-1,6/sedoheptulose-1,7-bisphosphatase (FBP/SBPase), enzymes responsible for RuBP regeneration and vital for controlling the CBB carbon flux, led to higher production rates and titers in ethanol producing strains of Synechocystis PCC 6803. In the present study, we investigated the combined effects of the above enzymes on ethanol production in Synechocystis PCC 6803.