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 K_m values of 59.39 mg L⁻¹ and V_max values of 47.03 mg L⁻¹ h⁻¹. The reduction in LB media followed Michaelis-Menten kinetics with K_m values of 99.52 mg L⁻¹ and V_max of 77.63 mg L⁻¹ h⁻¹. Scanning electron micrograms revealed the presence of extracellular polymeric secretions. [ABSTRACT FROM AUTHOR]