Reduction of hexavalent chromium by a novel Ochrobactrum sp. - microbial characteristics and reduction kinetics

A Gram negative hexavalent chromium (Cr(VI)) reducing bacteria, Ochrobactrum sp. Cr‐B4 (genbank accession number: JF824998) was isolated from the aerator water of an activated sludge process of a wastewater treatment facility of a dye and pigment based specialty chemical industry. It showed a resistance for 1000 mg L−1 Cr(VI). It exhibited resistance against other heavy metal ions like Ni2+ (900 mg L−1), Cu2+ (500 mg L−1), Pb2+ (800 mg L−1), and Cd2+(250 mg L−1), Zn2+ (700 mg L−1), Fe3+ (800 mg L−1), and against selected antibiotics. Cr‐B4 could efficiently reduce 200 mg L−1 Cr(VI) completely in nutrient and LB media and could convert Cr(VI) to Cr(III) efficiently. Cr(VI) reduction in nutrient media followed allosteric enzyme kinetics with Km values of 59.39 mg L−1 and Vmax values of 47.03 mg L−1 h−1. The reduction in LB media followed Michaelis–Menten kinetics with Km values of 99.52 mg L−1 and Vmax of 77.63 mg L−1 h−1. Scanning electron micrograms revealed the presence of extracellular polymeric secretions.