Functional analysis of hydrogen photoproduction in respiratory-deficient mutants of Chlamydomonas reinhardtii

In this paper, mitochondrial mutants of Chlamydomonas reinhardtii defective for respiratory complex I (NADH:ubiquinone oxidoreductase), complex III (ubiquinol cytochrome c oxidoreductase) and both complexes I and III were analyzed for H₂ photoproduction. Several parameters were followed during the S-deficiency stage and the anaerobic stage leading to H₂ photoproduction. At the early aerobic S-deficiency stage, starch and neutral lipids accumulated in all strains but their amount was significantly decreased in mutants compared to wild type. During the H₂ photoproduction process, whereas starch content strongly decreased in all strains, neutral lipid amount remained nearly unchanged, suggesting that starch degraded by glycolysis is the preferential substrate for energy production during anaerobiosis. The mutants displayed a decrease in H₂ photoproduction correlating to the number of active mitochondrial proton-pumping sites lost in the strains. Our results thus highlight the critical role of oxidative phosphorylation during the first (aerobic) stage of S-starvation when carbon resources are accumulated.