Oxygen sensitivity of algal H-2-production

Photoproduction of H-2 by green algae utilizes electrons originating from the photosynthetic oxidation of water and does not require metabolic intermediates. However, algal hydrogenases are extremely sensitive to O-2, which limits their usefulness in future commercial H-2-production systems. We designed an experimental technique for the selection of O-2-tolerant, H-2-producing variants of Chlamydomonas reinhardtii based on the ability of wild-type cells to survive a short (20 min) exposure to metronidazole in the presence of controlled concentrations of O-2. The number of survivors depends on the metronidazole concentration, light intensity, preinduction of the hydrogenase, and the presence or absence of O-2. Finally, we demonstrate that some of the selected survivors in fact exhibit H-2-production capacity that is less sensitive to O-2 than the original wild-type population.