image descriptionPhotosynthetic microorganisms can often experience periods of anoxia, especially during the night when photosynthesis is not taking place. Chlamydomonas reinhardtii is a unicellular green alga, which contains several genes encoding for proteins involved in different fermentative pathways. The induction of two [FeFe]-hydrogenase enzymes and the corresponding [FeFe]-hydrogenase maturation proteins under anoxic conditions results in hydrogen and CO2 emission as minor products, together with the major production of formate, acetate and ethanol. Anoxia can be induced to Chlamydomonas cultures by means of sulphur starvation (light anoxia) or by removing oxygen from the environment by sparging cultures with an inert gas (dark anoxia).
Research on Chlamydomonas is focused on its ability to acclimate to dark anoxia by inducing different fermentative pathways, with the major goal of increasing hydrogen production as a source of renewable energy.

We found that the regulation of the anaerobic gene expression in Chlamydomonas is only partly explained by responses to anoxia. The cell cycle and light–dark cycles are equally important elements in the regulatory network modulating the anaerobic response in Chlamydomonas.