Screening of Chlamydomonas mutants affected in starch breakdown and H2 production

Vincent Chochois and Laure Constans, Audrey Beyly, Pascaline Auroy, Laurent Cournac, and Gilles Peltier

CEA Cadarache, DSV, Institut de Biologie Environnementale et de Biotechnologie, Laboratoire de Bioénergétique et Biotechnologie des Bactéries et Microalgues, UMR 6191 CNRS/CEA/Université d'Aix-Marseille, Saint-Paul-lez-Durance, F-13108 France

The unicellular green alga Chlamydomonas reinhardtii is able to produce hydrogen in the light by a hydrogenase coupled to its photosynthetic electron transport chain. Although producing hydrogen from solar energy and water is of a considerable interest, biotechnological applications are limited by the oxygen-sensitivity of the hydrogenase. Taking advantage of algal metabolic flexibility, a time-based separation of hydrogen and oxygen production phases can be used to circumvent this limitation. Carbohydrate compounds (mainly starch) accumulate during the oxygenic phase and are subsequently converted to hydrogen during an anoxic phase, through a photosystem I (PSI)-dependent process. Reactions of starch to hydrogen conversion, which constitute the limiting part of the process, are poorly characterized. With the aim to identify molecular actors of the metabolic pathways involved in hydrogen photoproduction, we developed a genetic approach consisting in screening an insertion mutants library by iodine (a starch dye) staining. About 15,000 insertion mutants were screened based on starch mobilization properties in aerobic/dark and anoxic/light culture conditions. We report on the preliminary characterization of several of these mutants which are affected in hydrogen production.

e-mail address of presenting author: vincent.chochois@cea.fr