Both cell envelope and cytoplasm were the locations for chromium(VI) reduction by Bacillus sp. M6

Biotreatment is an effective way in remediation of chromium(VI) (Cr(VI)) contamination, but its mechanism and reaction sites are still not clear. Herein, Bacillus sp. M6 was used as a model bacterium in this study to investigate the removal mechanism of Cr(VI) in solution. The results showed that the removal of Cr(VI) was attributed to direct reduction by Bacillus sp. M6, and the reduction locations occurred both on the cell envelope and in the cytoplasm. Meanwhile, bioanalysis of Bacillus sp. M6 by SEM-EDS and TEM-EDS, indicated that Cr(III)-containing precipitates distributed both on the surface and in the cytoplasm of Bacillus sp. In addition, XPS analysis demonstrated that the chromium could be bound to cells by coordination with functional groups (C-based and O-based) on the bacterial surface. This work offers a new and deep insight into the mechanism of Cr(VI) reduction by Bacillus sp.