ABSTRACT
The processes investigated most extensively were based on nitrogenase-mediated hydrogen production by blue-green algae (cyanobacteria) and photosynthetic bacteria. This chapter reviews physiological aspects of biological hydrogen evolution and discusses potential applications of genetic manipulation. More than 40 years ago, Gest and Kamen first observed light-dependent evolution of molecular hydrogen by photosynthetic bacteria. Photoevolution of hydrogen has been observed in nitrogen-free media or at a very low level of nitrogen sources. In many cases, however, glutamate can be a good nitrogen source and stimulate the hydrogen evolution rate. To further increase the hydrogen molar yield and production rate of the system, the light-driven hydrogen evolution of photosynthetic bacteria is required. The genetics of hydrogenase is significantly advanced, especially in hydrogen bacteria, root nodule bacteria, and photosynthetic bacteria, and manipulation of the hydrogenase gene might be a ready-made key to an increased hydrogen production.
