title: Inducible chromate reductase exhibiting extracellular activity in Bacillus methylotrophicus for chromium bioremediation.
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 12h 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.
authors.affiliation: Department of Biotechnology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India.
authors.forename: John Geraldine
authors.initials: JG
authors.lastname: Sandana Mala
authors.affiliation: Department of Biotechnology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India.
authors.forename: Dhanasingh
authors.initials: D
authors.lastname: Sujatha
authors.affiliation: Department of Biotechnology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India. Electronic address: chellanrose@yahoo.co.uk.
authors.forename: Chellan
authors.initials: C
authors.lastname: Rose
mesh_terms: D001407:Bacillus / Q000235:genetics / Q000378:metabolism*; D001673:Biodegradation, Environmental; D002840:Chromates / Q000378:metabolism; D002857:Chromium / Q000378:metabolism*; D004789:Enzyme Activation; D005110:Extracellular Space / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000378:metabolism; D007700:Kinetics; D008670:Metals / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D013696:Temperature
chemical_list: D002840:Chromates; D007477:Ions; D008670:Metals; D002857:Chromium; D010088:Oxidoreductases; C063243:chromate reductase
keywords: Bacillus methylotrophicus; Bioremediation; Chromate reductase; Chromium toxicity; Tannery effluent