A bacterial laccase gene designated as lac21 was screened from a marine microbial metagenomic library of the South China Sea based on sequence screening strategy. The protein encoded by lac21 shared less than 40% sequence identities with all of the laccases found. Lac21, which was recombinantly expressed in Escherichia coli, showed high activity toward syringaldazine at an optimum pH of 7.5 and temperature of 45 degrees C. Lac21 was stable at pH values ranging from 5.5 to 9.0 and temperatures lower than 40 degrees C. Interestingly, chloride enhanced the laccase activity, with concomitant increase in substrate affinity. Furthermore, Lac21 has high decolorization capability toward azo dyes in the absence of redox mediators, with 80% of Reactive Deep Blue M-2GE (50 mg/L) being decolorized by 15 U/L enzyme after 24 h incubation at 20 degrees C. These unusual properties demonstrate that the new bacterial laccase Lac21 has potentials in specific industrial or environmental applications. 2012 Elsevier Ltd. All rights reserved.