Isolation and characterization of an alkali and thermostable laccase from a novel Alcaligenes faecalis and its application in decolorization of synthetic dyes.

A laccase producing new bacterial strain (Alcaligenes faecalis XF1) was isolated from green site of Chandigarh (India) by standard screening method. Nutrient broth medium containing 0.2 mM CuSO4 was used for the production of laccase. Maximum production (110 U/ml) was achieved after four days of incubation. The extracellular laccase from the medium was purified by simple salt precipitation and ion exchange technique to get 3.8 fold purified protein with 1637.8 U/mg specific activity. Purified laccase (named as LAC1*) revealed its optimum activity at pH 8.0 and 80 °C temperature, and displayed remarkable stability in the range of 70-90 °C and in the pH range (pH 7.0-9.0). The single bands on SDS-PAGE represents the purity of LAC1* with molecular weight of ∼71 kDa. The kinetic parameters for 2,6-DMP oxidation was Km, Vmax and kcat were 480 µM, 110 U/mL and 1375 s-1. Enzyme activity of the LAC1* was significantly enhanced by Cu2+, Mg2+, Mn2+, SDS and NaCl, and was slightly inhibited in the presence of conventional inhibitors like cysteine, EDTA and sodium azide. Extracellular nature and significant stability of LAC1* under extreme conditions of temperature, pH, heavy metals, halides and detergents confined its suitability for various biotechnological and industrial applications which required these qualities of laccase. So after recognizing all these properties the purified laccase was studied for its application in decolorization of industrial dyes.