What is it about?

Photosynthetic hydrogen production in green algae is catalyzed by the oxygen-sensitive hydrogenase enzyme, which accepts electrons from the photosynthetic apparatus located in the algal chloroplast and reduces protons of water to molecular hydrogen (H2). Since the process occurs downstream of photosystem I, the contribution of photosystem II (PSII) in H2 photoproduction has long been a subject of debate. Indeed, water oxidation by PSII results in the accumulation of molecular oxygen in chloroplasts, which inhibits H2 evolution. Therefore, clear evidence for direct water biophotolysis resulting in simultaneous H2 and O2 releases in algae has never been presented. This paper demonstrates that sustained H2 photoproduction in algal cells is directly linked to PSII-dependent water oxidation.

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Why is it important?

This research shows that algae are capable of producing molecular hydrogen (H2 gas) via the most efficient mechanism of direct water biophotolysis.

Perspectives

The most exciting moment in this research was the observation of the simultaneous production of hydrogen gas and the O(18)-labeled oxygen originating from oxidation of the O(18)-labeled water, thus confirming that algae can photosynthetically split water to H2 and O2.

Dr Sergey N Kosourov
Turun Yliopisto

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This page is a summary of: Water oxidation by photosystem II is the primary source of electrons for sustained H 2 photoproduction in nutrient-replete green algae, Proceedings of the National Academy of Sciences, November 2020, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2009210117.
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