A power-law sensitivity analysis of the hydrogen-producing metabolic pathway in Chlamydomonas reinhardtii

Melis et al. have demonstrated that the green alga Chlamydomonas reinhardtii, when deprived of sulfur, can produce hydrogen gas for ∼70 h, then can resume hydrogen gas production after a brief period of “recharging” in the presence of sulfur. Here we describe an S-system model of H2 production by C. reinhardtii. Through that model we investigate the sensitivity of H2 production to photosynthetic efficiency, and to contention for the protons produced by the photolysis of water, between hydrogen production on the one hand, and ATP consumption by cellular functions outside the H2 production path on the other. The model identifies for experimental investigation several potential systemic constraints on any genetic re-engineering effort aimed at increasing the H2 production efficiency of the alga.