Effect Of Dissimilated Iron Reduction On The Biodegradation Of Sulfonamides And Reduction Of Cr(?) By Shewanella Oneidensis MR-1

Sulfonamides?SAs?and chromium compounds are widely used in pharmaceutical and industrial production,which have caused certain environmental pollution.And all of these pollution problems are getting more and more attention.Dissimilatory iron-reducing bacteria is a kind of microorganism that can not only use Fe?III?but also other metals and organic compounds as the terminal electron acceptor.The dissimilatory reduction process has important influence on iron geochemical migration,which can affect the morphology distribution of metals,non-metallic,and the degradation of organic compounds.In this paper,we use the S.oneidensis MR-1 to degradate two kinds of SAs?SMX,SPY?and transformat Cr?VI?,And investigated the optimum conditions for degradation and reduction.Finally,we further explored the mechanism of degradation and reduction.The main research contents and results are as follows:1)In the indoor simulated conditions,we evaluate the antibiotic resistance,degradation kinetics,influencing factors and degradation products of SPY and SMX by S.oneidensis MR-1.The results show that the growth of S.oneidensis MR-1 was inhibited by the addition of SPY or SMX in the medium.S.oneidensis MR-1 were resistant to SPY and SMX concentrations as high as 60 mg/L.About 23.9%of SPY and 59.9%of SMX contained in the medium were degraded by S.oneidensis MR-1,respectively,after incubation for 5 days.The higher initial concentration of SPY and SMX,the degradation rate were decreased.The initial pH range of 7.0⁸.0 is suitable for S.oneidensis MR-1 to degrade SAs.When the five SAs were mixed together,the order of degradation was SMX>SPY>ST>SM2>SDZ by S.oneidensis MR-1.The degradation products of SPY and SMX were measured by LC-MS,with SPY as a substrate,2-AP?2-aminopyridine?was the main stable metabolite,and with SMX as a substrate,3A5MI?3-amino-5-methyl-isoxazole?was the main stable metabolite.The co-occurrence of 2-AP or 3A5MI and4-aminobenzenesulfonic acid suggests that the initial step in the biodegradation of the two sulfonamides is S–N bond cleavage.2)Dissimilatory iron-reducing could affect the degradation of pollutants.In this study,dissimilatory iron reduction can promote the degradation of SAs by S.oneidensis MR-1.About 53.5%of SPY and 97.9%of SMX was degradated after several days.But Fe?OH?₃is easier to be used than Fe₃O₄.AQDS will strengthen the dissimilation iron reduction and promote the degradation of SMX by electron transfer.And the electrochemical reaction results also showd that the current response values increased with the concentration of AQDS.3)The effects of different heavy metals on the dissimilation and reduction by S.oneidensis MR-1 were investegated.There were different degrees of inhibitory effects on the degradation of SPY and SMX when the concentration of metals(Pb²⁺,Cd²⁺,Zn²⁺and Hg²⁺)was 1 mg/L by S.oneidensis MR-1.However,As?V?could not be reduced and inhibits the degradation of antibiotics by S.oneidensis MR-1.4)Different concentrations of Cr?VI?had effect on the growth and metabolic activity of S.oneidensis MR-1,thereby inhibiting the reduction of Cr?VI?.The optimum pH of the strains growth was neutral and the weakly alkaline environment.The results of SEM-EDS and XPS showed that Cr?VI?and Cr?III?existed on the surface of cells,which confirmed that Cr?VI?can be direct reducted by S.oneidensis MR-1.5)Dissimilatory iron-reducing can promote the reduction of Cr?VI?by S.oneidensis MR-1.At the same time,the effect of different concentration of Fe?III?on the reduction of Cr?VI?by S.oneidensis MR-1 had not significant difference.This may be because that the iron,which promotes the reduction of Cr?VI?by S.oneidensis MR-1,can be recycled in the reduction process of Cr?VI?.AQDS also can promote the effect of the dissimlatory iron-reduction of Cr?VI?by S.oneidensis MR-1.And when the system without S.oneidensis MR-1,AQDS could not reduce Cr?VI?.This indicates that AQDS itself can not reduction Cr?VI?and Fe?III?in the system,which mainly acts as the role of electronic shuttles.Through the SEM-EDS,TEM-EDS and XPS confirmed that S.oneidensis MR-1had the ability to reduce Cr?VI?.It preferred that Fe?III?was reduced to Fe?II?,then Fe?II?further reduced Cr?VI?.The dissimilatatory iron-reducing promoted the reduction of Cr?VI?.Cr?III?was found on the cell surface.and Cr?III?existed in the form of Cr2O3 and Cr?OH?3.