Abstract
Most of photosynthetic bacteria, green algae and cyanobacteria can produce hydrogen gas with hydrogenase or nitrogenase enzyme. Photosynthetic bacteria carry out nitrogenase-dependent hydrogen production by anoxygenic photosynthesis. Among oxygenic photosynthetic microorganisms, nitrogen-fixing cyanobacteria produce hydrogen and oxygen simultaneously under light conditions because of protection mechanism for nitrogenase against oxygen. Since hydrogenase-dependent hydrogen production by cyanobacteria and green algae is oxygen-sensitive, it is possible under limited conditions such as dark and anaerobic conditions, which is fermentation of endogenous starch or glycogen. The author studied on hydrogen production by these microorganisms including molecular breeding (heterologous expression of clostridial hydrogenase in a cyanobacterium; BBA, 2000). The hydrogen metabolism and trials for improvements of hydrogen productivity by mutagenesis will be reviewed.
