Metabolic networks during dark anoxia

The Chlamydomonas genome encodes diverse metabolic networks that generate energy during periods of dark anoxia. Core fermentation pathways under standard laboratory conditions primarily produce formate, ethanol and acetate, and evolve H2 and CO2. Mutants disrupted for genes encoding enzymes of the dominant fermentation pathways activate alternative pathways that generate various additional fermentation products including glycerol, lactate, and succinate. Intriguingly, aspects of fermentative metabolism occur in both the mitochondria and chloroplast, although we know little about the interplay between these organelles. The remarkable metabolic flexibility of Chlamydomonas during dark anoxia likely reflects the importance of generating ATP for survival during periods of anaerobiosis, a frequent condition experienced by this alga in its habitats. An informed understanding of fermentative carbon transformations and knowledge of excreted products are critical for determining how unicellular algae influence the microbiota of natural ecosystems and could potentially be leveraged for sustainable biotechnology applications.