Enterobacter cloacae CYS-25 strain was isolated from a chromate plant. This bacterium was capable of resisting high hexavalent chromium concentration and reducing Cr(VI) under aerobic condition. CrO42- stimulated the increase of bacterial size and production of compact convex paths containing chromium on the bacterial surface. The increase of bacterial size was caused by integrative growth but not extracellular polymeric substance hyperplasia. IR and SDS-PAGE analyses showed the extracellular polymeric substance (EPS) components were mainly proteins and had no obvious changes whether the strains were induced by Cr(VI) or not. The EPS was amorphous and contained trivalent chromium. Under CrO42- growth condition, the extracellular substance of Enterobacter cloacae CYS-25 strains and Cr(VI) had redox reaction. The products were Cr3+-protein complexes which formed a piece of compact convex paths on the surface of bacteria and prevented Cr(VI) from entering into cells.
Bioremediation has been a considerable method for treating Cr(Ⅵ ) contamination. Bacterial surface changes of Ochrobactrum anthropi during Cr biosorption was investigated in this study. We found that Cr adsorption capacity increased with the increase of initial Cr(Ⅵ ) concentration. Atomic force microscope (AFM) morphologic analysis combined with surface roughness analysis indicated that the bacterial surfaces became rougher during Cr uptake process. X-ray photoelectron spectroscopy (XPS) showed that Cr(Ⅲ) was adsorbed on the bacterial surfaces. Fourier transform infrared (FT-IR) analysis showed that surface functional groups including C-O and C-N might be involved in the Cr biosorption process.
