Characteristics And Mechanisms Of Selenite Bioreduction By Shewanella Oneidensis MR-1 With Redox Mediators

With the development of industry,the situation of selenium pollution is more and more serious.Selenium in selenium-containing wastewater mainly exists in the form of selenate and selenite.Selenite is more common in the form of selenium than selenate.Selenite is easily soluble in water,easy to migrate,most toxic and harmful to the environment,which is one of the key research subjects of selenium pollution.In view of the low efficiency and long time-consuming of traditional biodegradable of selenite,this research was carried out by the strain S.oneidensis MR-1(accession No.ATCC 700550).Na₂Se O₃was selected as model pollutant.This study investigated the impact of four water-soluble quinone redox mediators(?-AQS,AQS,1,5-AQDS and AQDS)on bioreduction of selenite by S.oneidensis MR-1 and choosed the optimal mediators.The purpose of this research is to explore the characteristics and mechanisms of selenite bioreduction by S.oneidensis MR-1 with redox mediators the optimal mediators.This study investigated the impact of redox mediators(?-AQS,AQS,1,5-AQDS and AQDS)on bioreduction of selenite by S.oneidensis MR-1 and optimized the bioreduction condition with S.oneidensis MR-1 and AQDS.The particles obtained from cultures were analyzed using Zeta potential analyzer.The results suggested that all four tested redox mediators were able to accelerate the reduction of selenite by Shewanella oneidensis MR-1,and AQDS was the best.The optimum conditions were AQDS concentration of 0.2mmol?L^-1,p H of 8.0 and temperature of 30?.Selenite of 0.5 mmol?L^-1was completely removed after 48h bioreduction by S.oneidensis MR-1 with optimum conditions.AQDS may influence the composition and content of the organic layer covering around selenium nanoparticles(Se NPs).This study could provide a foundation for partical application for selenite biodegradation.Seven kinds of respiratory chain inhibitors(rotenone,capsaicin,quinacrine,diuron,antimycin A,Na N₃and DCCD)were used to explore the electron transfer mechanism of selenite reduction with AQDS.An electron transport model was obtained according to the results.The selenite reduction process was inhibited by rotenone,capsaicin,quinacrine,diuron,antimycin A,Na N₃and DCCD,so it could be inferred that the NADH-Co Q oxidoreductase,NADH dehydrogenase,FAD dehydrogenase in complex II,Pigment b complex,cytochrome reductase cytochrome b,cytochrome oxidase,ATP synthase participated in the electron transfer process of selenite reduction.In order to investigate the role of glutathione(GSH)in the reduction of selenite by S.oneidensis MR-1,this study investigated the effects of selenite concentration,BSO(GSH synthesis inhibitor)and AQDS on selenite reduction rate and the effect of GSH content.The results suggested that the decrease of selenite concentration during the reduction of selenite by S.oneidensis MR-1 was accompanied by the decrease of GSH content,and the content of GSH also affected selenite reduction rate.GSH participated the selenite reduction progress by S.oneidensis MR-1.