Oxygen sensitivity of algal H2- production.

Photoproduction of H2 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 H2-production systems. We designed an experimental technique for the selection of O2-tolerant, H2-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 O2. The number of survivors depends on the metronidazole concentration, light intensity, preinduction of the hydrogenase, and the presence or absence of O2. Finally, we demonstrate that some of the selected survivors in fact exhibit H2-production capacity that is less sensitive to O2 than the original wild-type population.