Decolorization of dyes by recombinase CotA from Escherichia coli BL21 (DE3) and characterization of the purified enzyme

Abstract

Dyes are usually difficult to be decolorized due to their complex chemical structures. In this work, recombinant CotA laccase was purified from Escherichia coli to evaluate its application in dye decolorization. Factors influencing laccase expression, such as induction temperature, phosphate buffer (pH), copper concentration and isopropyl β-D-1-thiogalactopyranoside (IPTG) concentration, were investigated. The recombinant laccase was purified to electrophoretic homogeneity, and was estimated to have a molecular mass about 67.5 kDa. The CotA protein was stained red by syringaldazine after Native-PAGE. The purified enzyme showed a similar behaviour to the spores laccase produced by Bacillus subtilis WD23. Using syringaldazine as the substrate to determine the CotA laccase activity, the optimum pH and temperature were 7.2 and 45°C, respectively. High laccase activity was maintained in a pH range from 6.0~7.6. The temperature half-life of the CotA laccases was 95 min at 80°C. The pH half-life was 8 h at pH 9.0 he CotA laccase was strongly inhibited by ethylenediaminetetraacetic acid (EDTA) and methyl alcohol. The CotA laccase could efficiently decolorize anthraquinone and azo dyes in 24 h. The decolourization capacity of this recombinant laccase suggested that it could be a useful biocatalyst for the treatment of dye-containing effluents.

Key words: Recombinant CotA laccase, Escherichia coli, purification, dye decolorization.