Algae after dark: mechanisms to cope with anoxic/hypoxic conditions

Chlamydomonas reinhardtii is a unicellular, soil-dwelling (and aquatic) green alga that has significant metabolic flexibility for balancing redox equivalents and generating ATP when it experiences hypoxic/anoxic conditions. The diversity of pathways available to ferment sugars is often revealed in mutants in which the activities of specific branches of fermentative metabolism have been eliminated; compensatory pathways that have little activity in parental strains under standard laboratory fermentative conditions are often activated. The ways in which these pathways are regulated and integrated have not been extensively explored. In this review, we primarily discuss the intricacies of dark anoxic metabolism in Chlamydomonas, but also discuss aspects of dark oxic metabolism, the utilization of acetate, and the relatively uncharacterized but critical interactions that link chloroplastic and mitochondrial metabolic networks.