Light Driven CO(2) Fixation by Using Cyanobacterial Photosystem I and NADPH-Dependent Formate Dehydrogenase

The ultimate goal of this research is to construct a new direct CO(2) fixation system using photosystems in living algae. Here, we report light-driven formate production from CO(2) by using cyanobacterial photosystem I (PS I). Formate, a chemical hydrogen carrier and important industrial material, can be produced from CO(2) by using the reducing power and the catalytic function of formate dehydrogenase (FDH). We created a bacterial FDH mutant that experimentally switched the cofactor specificity from NADH to NADPH, and combined it with an in vitro-reconstituted cyanobacterial light-driven NADPH production system consisting of PS I, ferredoxin (Fd), and ferredoxin-NADP(+)-reductase (FNR). Consequently, light-dependent formate production under a CO(2) atmosphere was successfully achieved. In addition, we introduced the NADPH-dependent FDH mutant into heterocysts of the cyanobacterium Anabaena sp. PCC 7120 and demonstrated an increased formate concentration in the cells. These results provide a new possibility for photo-biological CO(2) fixation.