Anaerobic Acclimation in Chlamydomonas reinhardtii ANOXIC GENE EXPRESSION, HYDROGENASE INDUCTION, ANDMETABOLIC PATHWAYS*□S

Both prokaryotic and eukaryotic photosynthetic microbes experience conditions of anoxia, especially during the night when photosynthetic activity ceases. In Chlamydomonas rein-hardtii, dark anoxia is characterized by the activation of an extensive set of fermentation pathways that act in concert to provide cellular energy, while limiting the accumulation of potentially toxic fermentative products. Metabolite analyses, quantitative PCR, and high density Chlamydomonas DNA microarrays were used to monitor changes in metabolite accu-mulation and gene expression during acclimation of the cells to anoxia. Elevated levels of transcripts encoding proteins associ-ated with the production of H2, organic acids, and ethanol were observed in congruence with the accumulation of fermentation products. The levels of over 500 transcripts increased signifi-cantly during acclimation of the cells to anoxic conditions