Isolation and characterization of a Cr[VI] reducing Bacillus firmus strain from industrial effluents

A chromium resistant bacterial strain KUCr1 exhibiting potential Cr(VI) reducing ability under in vitro aerobic condition is reported. The bacterial strain showed varied degree of resistance to different heavy metals. The MIC of chromium to this strain was found to be 950 mM under aerobic culture condition in complex medium. The factors affecting Cr(VI) reduction by this strain under culture condition were evaluated. Maximal Cr(VI) reduction was observed at the pH 8 to 10 and at a temperature of 35°C. Higher concentration of Cr(VI) slowed down the reduction, eventually all the metal could be reduced with longer incubation time. Different toxic metals showed differential effect on reduction. Cadmium and zinc were found to inhibit reduction. Cr(VI) reduction and bioremediation were found to be related to the growth supportive condition in terms of carbon, phosphorous and nitrogen supply in wastewater fed with tannery effluent indicating cell mass dependency of Cr(VI) reduction. Through biochemical characterization and 16S rDNA sequence analysis, the strain KUCr1, as the name given to it, was identified as a strain of Bacillus firmus.