Introducing Extra NADPH Consumption Ability Significantly Increases the Photosynthetic Efficiency of Cyanobacteria

Increasing photosynthetic efficiency is crucial to increasing biomass production to meet the growing demands for food and energy. Theoretical arithmetic analysis indicated that 2.57 ATP/2 NADPH are generated in light reactions, whereas 3 ATP/2 NADPH are required for CO₂ fixation in dark reactions. This suggests that the light reactions and dark reactions are imperfectly coupled due to shortage of ATP supply, or accumulation of NADPH. Here we hypothesized that solely increasing NADPH consumption might increase the coupling of light reactions and dark reactions, thereby increasing the photosynthetic efficiency. To test this hypothesis, a synthetic NADPH consumption pathway was constructed and introduced into the cyanobacterium Synechocystis sp. PCC 6803. The resulting extra NADPH-consuming mutant grew much faster and achieved a higher biomass concentration. Further analyses of the photosynthetic oxygen evolution rate, chlorophyll fluorescence and P700 indicated that the activities of both photosystem II and photosystem I and the light saturation point of the NADPH-consuming mutant all significantly increased, conceiving that the ATP production was increased. Thus, we demonstrated that stimulating NADPH consumption is a promising strategy to improve photosynthetic efficiency and to enable utilization of high-intensity lights.