Photobiological hydrogen production and nitrogenase activity in some heterocystous cyanobacteria

Abstract

This chapter discusses the activities of nitrogenase and H2 evolution in three cyanobacterial strains and some factors that affected these activities. Nitrogen-fixing heterocystous cyanobacteria are potential candidates for the development of photobiological hydrogen production systems. They produce H2 under aerobic conditions using water as an electron donor. For example A. variabilis IAM M-58 was most active in H2 production, and the amount of H2 produced was markedly higher than that of the other species. Hydrogen metabolism in these cyanobacteria involves at least three enzymes: nitrogenase, uptake hydrogenase, and bidirectional hydrogenase. Some researchers favor hydrogenase over nitrogenase as the hydrogen evolving system because of its high energy efficiency, but it was reported that continued production of H2 in air was mediated by nitrogenase in the heterocysts. To develop the hydrogen producing systems by cyanobacteria based on nitrogenase activity, it is important to find cyanobacterial strains which have a high activity of H2 production.