| With increasing awareness of environmental problems caused by the current fossil-fuel-based energy such as the greenhouse effect, many efforts have been taken to develop clean and sustainable energy sources. Molecular hydrogen is one of the potential future energy sources and becomes more and more attention. The green alga Chlamydomonas reinhardtii has been recognized as an ideal candidate. However, the activity of hydrogenase (H2ase) in this organism is overwhelmly oxygen-sensitive. Therefore, how to reduce O2 content in the cell has became one of key scientific questions for enhancing H2 photoproduction in C. reinhardtii.It was previously reported that the chemical drug, NaHSO3 can reduce O2 content in cells of green algae. Therefore, it appears that treatment with NaHSO3 can enhance H2 production in C. reinhardtii. First of all, this thesis attempted to explore the scientific problem. Our results indicated that the changes in the rates of H2 photoproduction caused by treatment with different NaHSO3 concentrations are reflected as a parabola. Specifically, the rates of H2 production were found to be the maximum at an approximate concentration of 13 mM NaHSO3. An upward or downward shift in the NaHSO3 concentration gradually leads to a decrease in the rate of H2 photoproduction. Further, the results showed that treatment with 13 mM NaHSO3 greatly improved photobiological H2 production about 200 times and the accumulation of H2 can be achieved at 100μmol per 0.3 mg chlorophyll. Moreover, this increase in H2 photoproduction is mostly the result of reduced O2 content and enhanced H2ase activity. Compared to that sulfur-deprived strategy, treatment with NaHSO3 has faster maximum rate of H2 photoproduction (Vmax), higher conversion efficiency of light energy into H2 (LCE), shorter half-time for reaching the maximum accumulated H2 levels (t1/2), and cheaper cost because of no centrifuge procedure. We therefore concluded that treatment with NaHSO3 is an efficient, rapid, and economic strategy for improvement of photobiological H2 production in C. reinhardtii.In 2003, it has been reported that the addition of low concentrations of sulfur to the cultures could enhance H2 production in the sulfur-free culture. It seems likely that NaHSO3 can enhance H2 production in sulfur-free culture of C. reinhardtii, since NaHSO3 is also a kind of sulfur sources. Therefore, another aim of this thesis will attempt to investigate this scientific question. Our results indicated that the changes in the accumulations of H2 production caused by treatment with different NaHSO3 concentrations are reflected as a parabola. Specifically, the accumulation of H2 production were found to be the maximum at an approximate concentration of 20μM NaHSO3. An upward or downward shift in the NaHSO3 concentration gradually leads to a decrease in the accumulation of H2 production. Further, the results indicated that treatment with 20μM NaHSO3 resulted in double H2 amounts. Moreover, this increase in H2 photoproduction is mostly the result of increased chlorophyll content and improved conversion efficiency of light energy into H2 in this unicellular green alga.Based on these results, we conclude that NaHSO3 greatly enhances photobiological H2 production in the unicellular green alga C. reinhardtii. Further, this discovery will explore a novel strategy for the photobiological H2 production in microalgae.
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