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Chromate is widely used industrial pollutant which can be detoxified effectively using chromate reductase from chromium resistant bacteria. A soluble Cr(VI) reductase from Bacillus amyloliquefaciens (CSB 9) was extracted and purified to electrophoretic homogeneity through (NH4)2SO4 precipitation followed by dialysis and gel filtration chromatography with specific activity of 0.167 U/mg and 6% yield with 30.36-fold increase in purity. Based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the molecular weight of the purified enzyme was estimated to be ~ 116 KDa. Further, functional characterization with respect to pH, temperature and storage stability showed optimum Cr(VI) activity at 35 °C and pH 7.0 on standard analysis conditions. Using potassium dichromate as substrate, the enzyme kinetics showed maximum activity (Vmax) of 3.5 U/mL with its corresponding KM value of 27.78 μM and the second-order constant (Vmax/Km) 0.125 U/μM mL. The purified enzyme exhibited higher stability (μM/mg/min) when treated with additives such as metal ions K+ (1.3 ± 0.056), surfactant tween 80 (2.33 ± 0.52), inhibitor β-mercaptoethanol (0.67 ± 0.15) and organic solvent glycerol (1.33 ± 0.011). These remarkable qualities found with the chromate reductase produced by B. amyloliquefaciens (CSB 9) could make it an ideal candidate for bioremediation of hexavalent chromium under a wide range of environmental conditions.

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