Chlamydomonas Mutant hpm91 Lacking PGR5 is a Scalable and Valuable Strain for Algal Hydrogen (H2) Production

Renewable hydrogen (H2) photoproduction by Chlamydomonas reinhardtii offers an attractive approach virtually driven by solar energy. However, it is currently not scalable due to lacking ideal strains that hindered mainly by insufficient knowledge of the molecular regulation mechanism. Previously, we have reported a Chlamydomonas PGR5-deficient mutant named hpm91 capable of prolonged H2 production for 25 days with more than 30-fold yield increase relative to its wild type in 100 ml set-ups. Here, we report that hpm91 is largely scalable and valuable in terms of key issues in algal-H2 production. Up to 100-fold extention of H2-photobioreacter (HPBR; 10 L) was established, leading to an average of H2 output 7287 ml/10L-HPBR during 26 days of sulfur deprivation. We found that hpm91 was robust and remained metabolically active over a long period of sulfur deprivation, most likely due to decreased intracellular ROS relative to wild type. To understand the molecular mechanism of H2 metabolism underlying in hpm91, we performed iTRAQ quantitative proteomics and compared proteomic change profiles of wild type and hpm91 that undergo H2 production process. Major proteome changes of hpm91, based on identified differentially expressed proteins with known function, include modifications in photosynthetic antanna, primary metabolic pathways and anti-ROS responses. Together with successful isolation of new strain(s) with enhanced H2-producing capability relative to hpm91, we highlight that the strain (hpm91) is not only up-scalable but also valuable in both basic and applied research aiming at elucidation of the molecular regulation mechanisms of H2 photoproduction and development of advanced algal-H2 photoproduction biotechnology.