Overexpression, characterization, and dye-decolorizing ability of a thermostable, pH-stable, and organic solvent-tolerant laccase from Bacillus pumilus W3

Fungal laccases are typically unstable at high temperatures and alkaline conditions, thereby limiting their practical application. In this study, the novel laccase-producing Bacillus pumilus strain W3 was isolated from raw gallnut honey samples. The CotA–laccase gene was cloned from W3 and efficiently expressed by recombinant Escherichia coli in its biologically active form. The purified recombinant laccase had an extensive pH range for substrate catalysis. The enzyme was highly stable in alkaline pH and high temperatures, with considerable tolerance to NaCl and organic solvents. Laccase activity remained constant after 10 d of incubation at pH 9.0, whereas approximately 45% of the initial activity was detected after 10 h incubation at 80 °C. Two azo dyes and two anthraquinonic dyes could be efficiently decolorized by purified laccase in the presence of a mediator under alkaline condition. More than 90% decolorization was observed at pH 9.0 after incubation for 5 h. These unusual properties indicated a high potential of the novel CotA–laccase for industrial application on decolorisation of textile dyeing effluent.