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The microbial reduction of U(Ⅵ) by Bacillus sp.dwc-2,isolated from soil in Southwest China,was explored using transmission electron microscopy (TEM),X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES).Our studies indicated that approximately 16.0％ of U(Ⅵ) at an initial concentration of 100 mg/L uranium nitrate could be reduced by Bacillus sp.dwc-2 at pH 8.2 under anaerobic conditions at room temperature.Additionally,natural organic matter (NOM) played an important role in enhancing the bioreduction of U(Ⅵ) by Bacillus sp.dwc-2.XPS results demonstrated that the uranium presented mixed valence states (U(Ⅵ) and U(Ⅳ)) after bioreduction,which was subsequently confirmed by XANES.Furthermore,the TEM and high resolution transmission electron microscopy (HRTEM) analysis suggested that the reduced uranium was bioaccumulated mainly within the cell and as a crystalline structure on the cell wall.These observations implied that the reduction of uranium may have a significant effect on its fate in the soil environment in which these bacterial strains occur.