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 1000mgL(-1) Cr(VI). It exhibited resistance against other heavy metal ions like Ni2+ (900mgL(-1)), Cu2+ (500mgL(-1)), Pb2+ (800mgL(-1)), and Cd2+(250mgL(-1)), Zn2+ (700mgL(-1)), Fe3+ (800mgL(-1)), and against selected antibiotics. Cr-B4 could efficiently reduce 200mgL(-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 K-m values of 59.39mgL(-1) and V-max values of 47.03mgL(-1)h(-1). The reduction in LB media followed Michaelis-Menten kinetics with K-m values of 99.52mgL(-1) and V-max of 77.63mgL(-1)h(-1). Scanning electron micrograms revealed the presence of extracellular polymeric secretions.