Hydrogen production by algae

A variety of microorganisms can evolve H2 according to the following equation:2H+ + 2e +z H2. These include strict or facultative anaerobic bacteria, aerobic bacteria, blue-green and green algae. In aerobic bacteria and in blue-green algae H2 formations are restricted to N2-fixing species. Strict and facultative anaerobic bacteria as well as green algae (Chlamydomonas, Scenedesmus, Chlorella) form the gas only under O2 exclusion in the cultures. There is no clearcut demonstration for Hrformation by mosses, ferns and higher plants. Lists of the Hrforming organisms are compiled in Mortenson and Chen I and Schlegel and Schneider2. Since the redox potential of the couple 2H+ /H2 is -413 mV at pH 7.0, a low potential reductant is required for H2-formation to proceed in the cells. The reaction is also enzyme mediated. Cells may contain 3 clearly distinguishable enzymes catalyzing either uptake or evolution of H2 under physiological conditions (for a more detailed account and the references see Bothe and Eisbrenner3).