Photosynthetic hydrogen production as acclimation mechanism in nutrient-deprived Chlamydomonas

Green microalgae are able to sustain hydrogen evolution in the light under nutrient deprivation conditions. In the current study, the role of hydrogen photoproduction in the acclimation of Chlamydomonas reinhardtii cells to nutrient deficiency was investigated. In this regard, such physiological characteristics of algal cells as starch and adenosine triphosphate content, fatty acid composition, fermentation products, photosynthetic activity, cell mortality, culture recovery, and cell ultrastructure were compared between the hydEF-1 mutant lacking hydrogenase activity and its parent strain CC-425 under sulfur deficiency. The results showed an increased number of non-viable cells, altered cell ultrastructure, and modified lipid, carbohydrate, and energy metabolism in the mutant cells. We suggest that active hydrogenase provides benefits for algae acclimation to the anaerobic phase of nutrient deprivation by regulating intracellular redox and pH balance and improving performance of anaerobic metabolism.