Cr(VI) reduction by Enterococcus gallinarum isolated from tannery waste-contaminated soil

Hexavalent chromium Cr(VI) is a widespread environmental contaminant. Many microorganisms have been reported to detoxify hexavalent chromium. The present work is the first report of a strain of Enterococcus having the ability of resistance to and reduction of Cr(VI). This strain was isolated from tannery waste-contaminated soil and identified as Enterococcus gallinarum, by biochemical methods and 16S rDNA analysis. The strain also exhibited multiple heavy metals (Cu2+, Ni (2+), Pb2+, Co2+ and Zn2+) tolerance. It was found to reduce chromate to 100% at a concentration of 200 mg l(-1), in aerobic conditions. The cells reduced Cr(VI) under a wide range of temperatures (25-45A degrees C) and pH (7-11) with optimum at 37A degrees C and initial pH 10. The presence of other metals, such as Cu2+, stimulated Cr(VI) reduction, while Pb2+ and Ni (2+) had no significant effect on reduction ability by the strain. Assay with resting and permeabilized cells (treated with toluene and Triton X-100) demonstrated that the reduction of Cr(VI) is mediated by cell membrane bound or soluble proteins of the cell. The results obtained in this study have significance for the bioremediation of chromate pollution.