Strategies for improving oxygen tolerance of algal hydrogen production

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This chapter presents an account of a research to generate a Chlamydomonas reinhardtii mutant that is sufficiently tolerant to O2 to produce H2 under aerobic conditions. The availability of such a mutant may permit the development of a commercial photobiological H2 production system that is cost effective, renewable, scalable, and non-polluting. Given the generally low specificity of the two selective pressures, the surviving organisms were subsequently subjected to a positive screen using a chemochromic sensor that detects H2 evolved by the algae. Clones that were found to exhibit high H2 evolution activity in the presence of O2 were characterized in more detail using biochemical assays. The strategy currently employed consists of re-mutagenizing, re-selecting, and re-screening first generation mutants under higher selective stringency in order to accumulate single-point mutations, and thus, to further increase the O2 tolerance of the organism. Recent results include the isolation of a clone, 104G5 with 14 times higher tolerance to O2 than the wild-type (WT) and the isolation of first and second generation mutants with, respectively, 3-4 and 10 times higher tolerance to O2 than the wild-type (WT).