PNNL

Abstract

Continuously illuminated nitrogen-deprived Cyanothece sp. ATCC 51142 evolved H2 via dinitrogenase at rates up to 400 µmol•mg Chl-1•h-1 in parallel with photosynthetic O2 production. Notably, sustained co-production of H2 and O2 occurred over 100 h in the presence of CO2, with both gases displaying inverse oscillations which eventually dampened to stable rates. Oscillations were not observed when CO2 was omitted, while H2 and O2 evolution rates were positively correlated. In situ light saturation analyses of H2 production displayed dose-dependence and lack of O2 inhibition. Inactivation of photosystem II had substantial long-term effects but did not affect the short-term H2 production indicating that the process is also supported by photosystem I activity and oxidation of endogenous glycogen. Collectively, our results demonstrate that uninterrupted H2 production in unicellular diazotrophic cyanobacteria can be fueled by water photolysis without the detrimental effects of O2 and have important implications for sustainable production of biofuels.