Cr(VI) reduction by Cellulosimicrobium sp. isolated from tannery effluent

Cr(VI) is a toxic metal that has carcinogenic and mutagenic effects on all living organisms. In order to study the contribution of microbes towards Cr(VI) reduction into the less toxic Cr(III) form, an indigenous chromium-resistant bacterial strain (A8) was isolated from a tannery effluent. It was identified as Cellulosimicrobium sp. on the basis of morphological and biochemical characterization and 16S rRNA gene sequencing. It could tolerate up to 1800 μg mL^–1 of K2CrO4 and showed an optimum reduction (98.6%) of Cr(VI) at the concentration of 900 μg mL^–1 aerobically. Cell-free enzyme assay exhibited the reduction of Cr(VI) in vitro. A total of 4 synthetic materials, sand, PVC, stone, and rubber tubing, were used as solid support to evaluate the ability of the isolated chromium-resistant bacterial strain for biofilm formation. In column experiments among bacterial film-coated materials, sand exhibited an excellent Cr(VI) reduction (96%), while PVC pipe, rubber tubing, and stone showed 94.5%, 90%, and 88.4% reduction potential of Cr(VI), respectively, after 96 h of incubation. Fluorescent microscopy also revealed that bacterial biofilm was distributed thoroughly on the surface of the sand particles. FTIR spectroscopy showed mainly the involvement of the glycerol units, polysaccharides, and C-N (alkyl) functional groups of the bacterial strain (A8) in the reduction of Cr(VI).