Environmental contamination of hexavalent chromium [Cr(VI)] is of serious concern for its toxicity as well as mutagenic and carcinogenic effects. Bacterial chromate reduction is a cost-effective technology for detoxification as well as removal of Cr(VI) from polluted environment. Chromium resistant and reducing bacteria, belonging to Arthrobacter, Pseudomonas, and Corynebacterium isolated from chromite mine overburden and seepage samples of Orissa, India, were found to tolerate 12–18？mM Cr(VI) during growth. Viable cells of these isolates were also capable of growing and reducing 100？μM Cr(VI) quite efficiently in Vogel Bonner (V.B.) broth under batch cultivation. Freshly grown cells of the most potent isolate, Arthrobacter SUK 1201, reduced 100？μM Cr(VI) in 48？h. Reduction potential of SUK 1201 cells decreased with increase in Cr(VI) concentration but increased with increase in cell density and attained its maximum at 1010？cells/mL. Chromate reducing efficiency of SUK 1201 was promoted in the presence of glucose and glycerol while the highest reduction was at pH 7.0 and 25°C. The reduction process was inhibited by divalent cations Ni, Co, and Cd, but not by Cu. Similarly, carbonyl cyanide m-chlorophenylhydrazone, N,N,-Di cyclohexyl carbodiimide, sodium azide, and sodium fluoride were inhibitory to chromate reduction, while 2,4 dinitrophenol promoted the process. Cells permeabilized by toluene increased the efficiency of Cr(VI) reduction and, thereby, indicate that Arthrobacter sp. SUK 1201, indigenous to chromite mining environment, could be used as an ideal tool for chromium bioremediation. 1. Introduction Mining activities in and around chromite mines, in general, lead to the generation of huge amount of overburden material as well as accumulation of mine seepage waters, which are the main sources of chromium pollution of inland fresh water and farm lands in the vicinity of the mining sites. The chromite mining in the vast area of Orissa, India, is no exception to this generalization [1, 2]. In humans, several health hazards are associated with continuous exposure to Cr(VI). This is mainly because of its carcinogenic as well as mutagenic properties. Workers employed in areas highly contaminated with chromium suffer from nasal irritation and ulceration, skin irritation, eardrum perforation, lung carcinoma [3, 4], bronchial asthma, kidney necrosis, and allergic reactions in the skin. At higher level, chromium is also found to cause oxidative damage to cell membrane, alteration of enzyme specificity, and structural deformation in DNA [5]. Conventional
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