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Microbiological Research
Vol. 170, 2015, Pages: 235–241

Inducible chromate reductase exhibiting extracellular activity in Bacillus methylotrophicus for chromium bioremediation

John Geraldine Sandana Mala, Dhanasingh Sujatha, Chellan Rose

Department of Biotechnology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India.

Abstract

Chromium toxicity is one of the major causes of environmental pollution due to its heavy discharge in industrial wastewaters. Chromate reduction is a viable method to detoxify hexavalent chromium to nontoxic trivalent species mediated by enzymes and metabolites. A new Bacillus methylotrophicus strain was isolated from tannery sludge and was an efficient candidate for chromate reduction. An initial chromate reductase activity of 212.84 U/mg protein was obtained at 48 h in a low-cost defined medium formulation with 0.25 mM chromate. The extracellular enzyme was inducible at 12 h substrate addition with 312.99 U/mg at 48 h. Reduced glutathione was required for enhanced specific activity of 356.48 U/mg. Enzyme activity was optimum at pH 7.0 and at 30°C, and was stable in the presence of EDTA, DTT and metal ions. The enzyme exhibited a Vmax of 59.89 μM/min/mg protein and a Km of 86.5 μM, suggesting feasibility of the reaction with K2Cr2O7 as substrate. Application of the crude reductase in tannery effluent resulted in 91.3% chromate reduction at 48 h. An enzyme-mediated chromate reduction process has therefore been developed for bioremediation of toxic chromium sp. in industrial effluents.

Keywords: Bacillus methylotrophicus; Bioremediation; Chromate reductase; Chromium toxicity; Tannery effluent.


 
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