Hexavalent chromate reduction in soil microcosm using bacterial consortium

Hexavalent chromium is a toxic heavy metal used in different industries and causes environmental and health problems. In this study three bacterial isolates capable of growing at high concentration of chromium were recovered from Chromium polluted sludge. Chromium reduction was optimized and the optimum pH, temperature and aeration were 7, 30 C 200 rpm respectively for all isolates. The bacterial isolates were identified by 16S rRNA gene sequence analysis as Bacillus sp., Streptomyces rochei and Pseudomonas sp.. The isolates were mixed and tested as a consortium in Cr(VI) contaminated soil microcosm and showed complete removal of Cr(VI) in soil containing 200 mg Kg-1 and 400 mg Kg-1 after 4 and 7 days of incubation respectively. To determine the possible mechanism of Cr(VI) detoxification, cells of Bacillus sp. and Streptomyces rochei were sonicated after growth on media containing chromate and partial accumulation of chromate inside the bacterial cells was detected. Scanning electron micrograph and Energy dispersive X-ray analysis (EDX) showed adhesion of chromium on cells surface. Transmission electron micrograph showed accumulation of chromium particles inside the cells. The mixed consortium could be used for the bioremediation of waste containing hexavalent chromium.