Biochemical characteristics of a textile dye degrading extracellular laccase from a Bacillus sp. ADR

Bacillus sp. ADR secretes an extracellular laccase in nutrient broth, and this enzyme was purified up to 56-fold using acetone precipitation and DEAE-cellulose anion exchange chromatography. The molecular weight of purified laccase was estimated to be 66kDa using sodium dodecyl sulfate polyacrylamide gel electrophoresis. The purified laccase oxidized 2,6-dimethoxy phenol, o-tolidine, hydroquinone, l-DOPA and guaiacol. The optimum pH for oxidation of o-tolidine, 2,6-dimethoxy phenol and guaiacol were 3.0, 4.0 and 5.0, respectively. The purified laccase contained 2.7mol/mol of copper. The laccase was stable up to 40°C and within the pH range of 7.0–9.0. Well-known inhibitors of multicopper oxidases such as, sodium azide, l-cysteine and dithiothreitol showed significant inhibition of laccase activity. The purified enzyme decolorized structurally different azo dyes with variable decolorization rates and efficiencies of 68–90%. This study is useful for understanding the precise use of Bacillus sp. ADR in the decolorization of textile dyes containing industrial wastewater.