The electron transfer pathway upon H2 oxidation by the NiFe bidirectional hydrogenase of Synechocystis sp. PCC 6803 in the light shares components with the photosynthetic electron transfer chain in thylakoid membranes

In anaerobic conditions the NiFe hydrogenase in the cyanobacterium Synechocystis sp. PCC 6803 catalyzes transient H2 production upon a darkness-to-light transition, followed by a rapid H2 uptake. We measured H2 uptake in Synechocystis mutants lacking photosystem I, photosystem II or terminal oxidases and in the wild-type strain with and without active cytochrome b6f. Rapid light-induced H2 uptake was dependent on cytochrome b6f and the presence of photosystem I. We propose light-dependent electron transport from H2 to plastoquinone, probably via NAD(P)H dehydrogenase, and on to cytochrome b6f and photosystem I. In darkness H2 uptake is ∼10-fold slower than in the light and is independent of thylakoid redox components. The plastoquinone redox state may be key in determining the ultimate H2 redox partner. H2 uptake and production in darkness likely use the same redox partners. NADH and NADPH, but not reduced ferredoxin, were confirmed as hydrogenase redox donors in vitro.