Water-splitting-based, sustainable and efficient H2 production in green algae as achieved by substrate limitation of the Calvin-Benson-Bassham cycle.

BACKGROUND: Photobiological H2 production has the potential of becoming a carbon-free renewable energy source, because upon the combustion of H2, only water is produced. The [Fe-Fe]-type hydrogenases of green algae are highly active, although extremely O2-sensitive. Sulphur deprivation is a common way to induce H2 production, which, however, relies substantially on organic substrates and imposes a severe stress effect resulting in the degradation of the photosynthetic apparatus. RESULTS: We report on the establishment of an alternative H2 production method by green algae that is based on a short anaerobic induction, keeping the Calvin-Benson-Bassham cycle inactive by substrate limitation and preserving hydrogenase activity by applying a simple catalyst to remove the evolved O2. Cultures remain photosynthetically active for several days, with the electrons feeding the hydrogenases mostly derived from water. The amount of H2 produced is higher as compared to the sulphur-deprivation procedure and the process is photoautotrophic. CONCLUSION: Our protocol demonstrates that it is possible to sustainably use algal cells as whole-cell catalysts for H2 production, which enables industrial application of algal biohydrogen production.