Life Sciences Division

Some micro-organisms that carry out oxygenic photosynthesis, such as the unicellular algae Chlamydomonas reinhardtii, possess a hydrogenase enzyme that enables them to produce molecular hydrogen using water as a source of electrons and sunlight as a source of energy. While this reaction can be used to produce hydrogen from renewable energy sources, the biotechnological applications are limited due to the transient nature of hydrogen photoproduction. Hydrogenase is extremely sensitive to the presence of oxygen produced during photosynthesis using photosystem 2 (PSII). Effective control of PSII is therefore a key factor in maintaining an algal culture at conditions that promote the production of hydrogen. PSII is essential to algal growth under autotrophic conditions making it necessary to develop methods that enable the controlled alternation of photosynthetic growth phases with hydrogen production phases. Accordingly, researchers at the Bacterial and Microalgal Bioenergetics and Biotechnology Laboratory (LB3M, IBEB Cadarache), jointly with the J.D Rochaix laboratory (Geneva University, Switzerland), have shown that a new type of genetic switch can be used to effectively control photosystem II activity. The selected strategy consists in putting a nuclear factor (Nac2, which regulates the expression of the psbD gene which plays a key role in the functioning of PSII) under the control of the cytochrome c6 promoter, which is repressed in the presence of copper. Adding copper (Cu2+) to the culture media inhibits photosynthetic activity in Chlamydomonas strains carrying this construction. Mass spectrometry measurements of gaseous exchange revealed the potential of this system for inducing the hydrogen production process. It takes less than three hours after the addition of Cu2+ to reach a state of anoxia and trigger hydrogen production. Current research is directed at explaining and optimising the electron transfer pathways that culminate in the production of hydrogen.