Hexavalent chromium reduction by Providencia sp.

A gram-negative chromate reducing bacteria (UTDM314) was isolated from the contaminated sites of chemical industries, which is identified as Providencia sp. by biochemical methods and 16SrRNA analysis. The bacterial isolate could grow and reduce chromate to 100% at a concentration ranging from 100–300 mg/l and 99.31% at a concentration of 400 mg/l, pH 7 and temperature 37 °C. It also exhibited multiple heavy metal (Ni, Zn, Hg, Pb, Co) tolerance. Assay with resting cells, permeablized cells (treated with toluene and Triton X100) and crude cell free extracts demonstrated that the hexavalent chromium reduction is mainly associated with the soluble fraction of the cell. Providencia sp. has a great potential for bioremediation of Cr(VI) containing wastes. This approach permits selection of bacterial strains, which could be used for specific environmental clean up operations.