Enzymatic Characteristics And Mechanisms Of Cr(?) Bioreduction By Mangrovibacter Plantisponsor Strain With Redox Mediators

Chromium and its compounds were widely used as a kind of important industrial raw materials,which generated a high economic value,but also caused serious chromium pollution.This research was carried out by the strain Mangroveibacter sp.(accession No.KF540843),previously separated from a tannery in Shijiazhuang,a Cr(?)reducing bacteria with quinone respiration.K2CrO4 and anthraquinone-2-sulfonic acid sodium(AQS)were selected as model pollutant and redox mediator,separately.The purpose of this research is to explore the enzymatic characteristics and mechanisms of Cr(?)bioreduction by Mangroveibacter sp.with AQS.Reduced products were multi-angle analyzed through several methods such as scanning electron microscopy and energy spectrum analysis(SEM&EDS),transmission electron microscopy analysis(TEM),fourier transform infrared spectroscop(FT-IR),X ray diffraction(XRD)and X ray photoelectron spectroscopy(XPS)etc.The results indicated that the toxicity of Cr(?)had a certain influence on the morphology of bacteria and functional groups on the surface of bacteria were not involved in the Cr(?)reduction process.Cr(?)reduced products were mainly deposited in the cell periphery as a Cr(?)form.Enzymatic mechanism of Cr(?)reductase was carried out through redox mediators,electron donors and inhibitors.The results showed that AQS and NADH could accelerate Cr(?)reduction.The activity of extracellular enzyme was the highest and the protein content of membrane enzyme was the most.The co-interaction of AQS and NADH could significantly accelerate Cr(?)reductio.The Cr(?)removal rate was lower with higher of Cr(?)initial concentration in a certain range.The optimum temperature was 35?,and the optimum pH was about 7.Eight kinds of respiratory chain inhibitors(Cu2+,rotenone,capsaicin,dicoumarin,quinacrine,CCCP,DCCD,NaN3)were used to explore the electron transfer mechanism of Cr(?)reduction with AQS.An electron transport model was obtained according to the results.The Cr(?)reduction process was inhibited by rotenone,so it could be inferred that the NADH-CoQ oxidoreductase participated in the electron transfer process of Cr(?)reduction.Capsaicin and DCCD both had a significant promoting role in this process,which suggested that NADH dehydrogenase and ATP synthase might compete with AQS electronics for bacterial metabolism,not for Cr(?)reduction,as the limiting step of electron transfer.Dicoumarin and NaN3 had not an obvious promoting effect,which suggested that menadione and cytochrome oxidase were involved in the electron transfer process.