Formation of soluble Cr(III) end-products and nanoparticles during Cr(VI) reduction by Bacillus cereus strain XMCr-6

The Bacillus cereus strain XMCr-6 was isolated from chromium-contaminated soils and was identified on the basis of biochemical characteristics and 16S rRNA gene sequence analysis. The bacterium exhibited complete reduction of 100 mg L-1 Cr(VI) within 48 h under aerobic conditions. The reduction of Cr(VI) by XMCr-6 was attributed to cell debris rather than cell free extract, and the reduction mechanism was found to be enzyme-mediated. It was demonstrated that the reduced Cr(III) could bind to cells by coordination with functional groups on the bacterial surfaces while it simultaneously formed soluble Cr(III) end-products through interactions with small organic molecules. Discrete spherical Cr2O3 nanoparticles were observed on the surface of the bacterial cells after Cr(VI) reduction by XMCr-6 in the absence of an appropriate chelating chemical. Our results offer insight into bacterial Cr(VI) reduction processes and will be valuable for understanding reduction mechanisms and Cr(VI) bioremediation. (C) 2012 Elsevier B.V. All rights reserved.