Hydrogen Photoproduction Is Attenuated by Disruption of an Isoamylase Gene in Chlamydomonas reinhardtii

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Abstract
DNA insertional transformants of Chlamydomonas reinhardtii were screened chemochromically for attenuated H2 production. One mutant, displaying low H2 gas photoproduction, has a nonfunctional copy of a gene that shows high homology to the family of isoamylase genes found in several photosynthetic organisms. DNA gel blotting and gene complementation were used to link this isoamylase gene to previously characterized nontagged sta7 mutants. This mutant is therefore denoted sta7-10. In C. reinhardtii, the STA7 isoamylase gene is important for the accumulation of crystalline starch, and the sta7-10 mutant reported here contains 7 h under anaerobic incubation. Complementation of mutant cells with genomic DNA corresponding to the STA7 gene restores both the starch accumulation and H2 production phenotypes. The results indicate that STA7 and starch metabolism play an important role in C. reinhardtii H2 photoproduction. Moreover, the results indicate that mere anaerobiosis is not sufficient to maintain hydrogenase gene expression without the underlying physiology, an important aspect of which is starch metabolism.