Loss of algal Proton Gradient Regulation 5 increases reactive oxygen species scavenging and H evolution.

We have identified hpm91, a Chlamydomonas mutant lacking Proton Gradient Regulation5 (PGR5) capable of producing hydrogen (H ) for 25 days with more than 30-fold yield increase compared to wild type. Thus, hpm91 displays a higher capacity of H production than a previously characterized pgr5 mutant. Physiological and biochemical characterization of hpm91 reveal that the prolonged H production is due to enhanced stability of PSII, which correlates with increased reactive oxygen species (ROS) scavenging capacity during sulfur deprivation. This anti-ROS response appears to protect the photosynthetic electron transport chain from photo-oxidative damage and thereby ensures electron supply to the hydrogenase.