It will identify photosynthetic mutants affected in the linear electron transport chain or in the chlororespiratory pathways, mutants with knockouts in genes essential for the biosynthesis and assembly of the FeFe-hydrogenase (Posewitz et al. 2004), or strains unable to carry out
the necessary selleck inhibitor gene-regulatory reactions. Thus, the putative mutant FK228 supplier strains need to be analyzed by additional screening steps as earlier described. Attenuation of the photosynthesis/respiration (P/R) capacity ratio in green microalgae as a tool for stabilizing H2 evolution and its metabolism A second screening system has been established in order to specifically identify C. reinhardtii mutant strains affected in the ratio of photosynthetic O2 evolution and respiratory O2 consumption (Rühle et al. 2008). Utilization of the cell’s own respiration to consume photosynthetically generated O2 has
proven to be a successful strategy for initializing hydrogenase activity in the algae. The balanced interaction between the two bioenergetic organelles in S-deprived cells is currently the only available platform for the further I-BET151 concentration investigation of H2 metabolism in microalgae (Melis and Happe 2001; Melis 2007), and offers the only approach available for a sustained photobiological hydrogen production. It is therefore desirable to develop transgenic microalgae in which the photosynthesis/respiration (P/R) capacity ratio of cells growing in nutrient-replete medium is genetically defined not to exceed the 1:1 ratio without altering the high-quantum yield of
photosynthesis. C. reinhardtii, and other green microalgae, naturally possess a photosynthesis/respiration (P/R) capacity ratio of about 4:1 (Melis et al. Cediranib (AZD2171) 2000; Zhang et al. 2002). Attenuating the cellular P/R capacity ratio to a value that is equal to or less than unity, without altering the high-quantum yield of photosynthesis, would permit C. reinhardtii to grow photo-heterotrophically in the presence of acetate. In sealed cultures, anaerobiosis would prevail, lifting the O2-dependent suppression of hydrogenase gene expression, which is the first step to permitting a light-dependent H2 evolution. Such constitutive expression of the FeFe-hydrogenase pathway and the resulting photosynthetic H2 metabolism would occur with physiological levels of S, or other nutrients, in the chloroplast. Accordingly, genes that lower the capacity of photosynthesis and/or enhance the capacity of respiration in C. reinhardtii, without altering the high-quantum yield of photosynthesis, are of keen interest in this field. The creation of appropriate C. reinhardtii mutants can be achieved by applying DNA insertional mutagenesis; however, the isolation of strains with the desired phenotype requires development of a specific and stringent high throughput screening protocol. The purpose of reaching photobiological H2 production under normal growth conditions excludes the usage of C.