A simple strategy for extracellular production of CotA laccase in Escherichia coli and decolorization of simulated textile effluent by recombinant laccase

Laccases are green oxidases with a number of potential industrial applications. In this study, recombinant Bacillus subtilis CotA laccase was secreted by Escherichia coli via both the alpha-hemolysin secretion system and the YebF secretion system after microaerobic induction. Meanwhile, we discovered a much simpler approach for extracellular production of recombinant CotA laccase from E. coli, involving alternation of induction conditions to release recombinant CotA following intracellular expression. By optimizing the induction parameters, the extracellular yield of recombinant CotA laccase was improved from 157.4 to 2401.3 U/L after 24 h of induction. This strategy could be suitable for large-scale production of CotA laccase for industrial use. Recombinant CotA laccase was purified by Ni2+ affinity chromatography in a single step and showed similar biochemical properties to wild-type laccase. Purified as well as crude recombinant CotA laccase efficiently decolorized seven structurally different dyes. The decolorization capability of recombinant CotA laccase under harsh conditions was investigated by incubation of the enzyme with a simulated textile effluent (STE) with pH 11.6, 3.5 % salinity and peak absorbance of 10.42. Recombinant CotA laccase efficiently decolorized 77.0 % of STE after 48 h reaction, demonstrating the potential of this enzyme for industrial dye effluent treatment.