BACKGROUND: The reduction of highly mobile and toxic hexavalent chromium by bacterial strains is considered to be a viable alternative to reduce Cr(VI) contamination, in soils and water bodies, emanating from the overburden dumps of chromite ores and mine drainage. The present study reports the isolation of Cr(VI) resistant bacterial strains from an Indian chromite mine soil and their potential use in reduction of hexavalent chromium. RESULTS: Among the isolates, a bacterial strain (CSB-4) was identified as Bacillus sp. based on standard biochemical tests and partial 16SrRNA gene sequencing, which was tolerant to as high as 2000 mg L-1 Cr(VI) concentration. The strain was capable of reducing Cr(VI) to Cr(III) in different growth media. Under the optimized conditions pH similar to 7.0, 100 mg L-1 Cr(VI), 35 degrees C temperature and stirring speed 100 rpm, CSB-4 reduced more than 90% of Cr(VI) in 144 h. The time course reduction data fitted well an exponential rate equation yielding rate constants in the range 3.22 x 10(-2) to 6.5 x 10(-3) h(-1) for Cr(VI) concentration of 10-500 mg L-1. The activation energy derived from temperature dependence rate constants between 25 and 35 degrees C was found to be 99 kJ mol(-1). The characterization of reduced product associated with bacterial cells by SEM-EDS, FT-IR and XRD was also reported. CONCLUSION: Reasonably high tolerance and reduction ability of indigenous Bacillus sp. (CSB-4) for Cr(VI) under a wide range of experimental conditions show promise for its possible use in reclamation of chromite ore mine areas including soils and water bodies. (C) 2010 Society of Chemical Industry