Study On Functional Mechanism Of Enhancing H₂ Photoproduction In Microalgae By Sodium Pyrosulfite Under Nature Conditions

Hydrogen has the highest calories per unit mass and is free from secondary pollution. It is well known that under nature conditions, photoproduction of H2 in microalgae is an optimal model to produce H2. However, hydrogenase is extremely sensitive to oxygen and consequently always limits the development of such H2 production model. To remove this limiting factor, various strategies for H2 photoproduction are carried out, for examples, genetic engineering, deficient nutrition and improved culture mode. However, little is achieved. These strategies are fulfilled under an airtight condition, which largely limit the industrial application of photobiological hydrogen production in microalgae.The aim of this thesis will try to find an efficient method to remove O2, which can enhance the yield of H2 photoproduction under nature conditions without airtight conditions, then, reveal its functional mechanism. The main results of this thesis are listed as follows:1) Under nature conditions, treatment with sodium pyrosulfite(3m M) can cause an about 100-fold increase in H2 photoproduction in Chlamydomonas reinhardti.2) Under high light conditions, sodium pyrosulfite treatment could rapidly reduce the content of O2 in cells, but were impeded by both DCMU that inhibits electron transfer from PSII to PSI and superoxide dismutase(SOD). It is well known that the superoxide anion induced by high light could be suppressed by DCMU and could be removed by SOD. Taking these results together, we can conclude that under conditions of high light, sodium pyrosulfite can react with superoxide anion produced at the acceptor side of photosystem I, thereby reducing O2 content, activating hydrogenase activity and producing H2.3) In addition to C. reinhardtii, the increase in H2 photoproduction by sodium pyrosulfite treatment can be also applied to Chlorella pyrenoidosa, Anabaena sp. strain PCC 7120 and Synechocystis sp. strain PCC 6803. Therefore, we suggest that under nature conditions, treatment with sodium pyrosulfite can widely enhance the yield of H2 photoproduction in microalgae.Based on the above results, we reveal that under nature conditions, sodium pyrosulfite can react with superoxide anion and consequently remove O2 in cells, thereby activating hydrogenase and enhancing H2 photoproduction in microalgae. This indicates that we can successfully achieve the photoproduction of H2 by microalgae under nature conditions, with sodium pyrosulfite eliminating oxygen that inhibits hydrogen production. Thus, this is a significant breakthrough in a history of H2 photoproduction in microalgae.