Department of Civil, Chemical, Environmental and Materials Engineering (DICAM), School of Engineering and Architecture, Alma Mater Studiorum, University of Bologna, Via U. Terracini 28, I-40131, Bologna, Italy.
New Phytol. 2014 Dec;204(4):890-900. doi: 10.1111/nph.12964. Epub 2014 Aug 8.
In anaerobiosis, the microalga Chlamydomonas reinhardtii is able to produce H2 gas. Electrons mainly derive from mobilization of internal reserves or from water through biophotolysis. However, the exact mechanisms triggering this process are still unclear. Our hypothesis was that, once a proper redox state has been achieved, H2 production is eventually observed. To avoid nutrient depletion, which would result in enhanced fermentative pathways, we aimed to induce long-lasting H2 production solely through a photosynthesis : respiration equilibrium. Thus, growing cells were incubated in Tris Acetate Phosphate (TAP) medium under low light and high chlorophyll content. After a 250-h acclimation phase, a 350-h H2 production phase was observed. The light-to-H2 conversion efficiency was comparable to that given in some reports operating under sulphur starvation. Electron sources were found to be water, through biophotolysis, and proteins, particularly through photofermentation. Nonetheless, a substantial contribution from acetate could not be ruled out. In addition, photosystem II (PSII) inhibition by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) showed that it actively contributed to maintaining a redox balance during cell acclimation. In appropriate conditions, PSII may represent the major source of reducing power to feed the H2 evolution process, by inducing and maintaining an ideal excess of reducing power.
在无氧条件下，小球藻能够产生氢气。电子主要来源于内部储备物质的动员或通过生物光解作用从水中获得。然而，触发这一过程的确切机制仍不清楚。我们的假设是，一旦达到适当的氧化还原状态，就会最终观察到氢气的产生。为了避免营养物质耗尽，从而导致发酵途径增强，我们旨在仅通过光合作用-呼吸平衡来诱导长时间的氢气产生。因此，将生长中的细胞在低光和高叶绿素含量下在三乙酸盐磷酸盐（TAP）培养基中孵育。经过 250 小时的适应阶段后，观察到 350 小时的氢气产生阶段。光到氢的转换效率与一些在硫饥饿条件下运行的报告中的给出的效率相当。电子源被发现是水，通过生物光解作用，以及蛋白质，特别是通过光发酵。然而，不能排除乙酸盐的大量贡献。此外，通过 3-(3,4-二氯苯基）-1,1-二甲基脲（DCMU）对光系统 II（PSII）的抑制表明，它在细胞适应过程中通过诱导和维持理想的还原能力过剩，积极有助于维持氧化还原平衡。在适当的条件下，PSII 可能代表了为氢气演化过程提供还原能力的主要来源，通过诱导和维持理想的还原能力过剩。
