Chromium (VI) reduction by cell free extract of Ochrobactrum anthropi isolated from tannery effluent

Chromium-resistant bacteria isolated from industrial wastes can be used to detoxify toxic chromium from contaminated sources. From effluent of Shafiq Tannery, Kasur, Pakistan, bacterial strain STCr-1 that could endure 40 mg mL(-1) of potassium chromate in nutrient agar medium was isolated. STCr-1, identified as Ochrobactrum anthropi by 16S rRNA gene sequence homology, demonstrated substantial Cr(VI) reduction at pH 7 and temperature 37°C. It completely reduced 250 μg mL(-1) of Cr(VI) and showed 71.2 % Cr(VI) reduction at Cr(VI) concentrations of 550 μg mL(-1). Rate of Cr(VI) reduction increased with increase in cell and Cr(VI) concentration. The presence of Cu(2+), Co(2+) and Mn(2+) significantly stimulated Cr(VI) reduction. Assay with cell free extracts clearly indicated that Cr(VI) reduction was solely associated with the soluble fraction of the cell.