Reduction of chromate by cell-free extract of Brucella sp. isolated from Cr(VI) contaminated sites

A locally isolated gram negative strain of Brucella sp., identified by biochemical methods and 16SrRNA analysis, reduced chromate to 100%, 94.1%, 93.2%, 66.9% and 41.6% at concentrations of 50, 100, 150, 200 and 300 mg l−1, respectively at pH 7 and temperature 37 °C. Increasing concentrations of Cr(VI) in the medium lowered the growth rate but could not be directly correlated with the amount of Cr(VI) reduced. The strain also exhibited multiple heavy metal (Ni, Zn, Hg, Pb, Co) tolerance and resistance to various antibiotics. Assay with crude cell-free extracts demonstrated that the hexavalent chromium reduction was mainly associated with the soluble fraction of the cell. High Cr(VI) concentration resistance and high Cr(VI) reducing ability of the strain make it a suitable candidate for bioremediation.