Characterization of laccase from Salipiger sp. CCB-MM3 with decolorization activity against azo, anthraquinone and triarylmethane dyes

Laccases are multicopper oxidases with potential applications in the decolorization of synthetic dyes such as azo, anthraquinone and triarylmethane dyes. The laccase from the marine bacterium Salipiger sp. CCB-MM3, Lac_MM3, is a monomer with a predicted Greek-key β barrel typical of laccases. Characterization of Lac_MM3 revealed that Cu²⁺ acted as an activator with an apparent binding constant of 174 μM. The presence of a peak at 600 nm indicated that Cu²⁺-loaded Lac_MM3 was a typical blue laccase. It functioned optimally at 40 °C within a narrow pH range of 3.0–4.0, with k_cat/K_m of 113.3 s⁻¹mM⁻¹ against the substrate ABTS. Decolorization assays towards 14 synthetic dyes showed that Lac_MM3 efficiently decolorized the azo dyes Direct Blue 71, Congo Red, and Acid Blue 113, as well as the anthraquinone dye Acid Blue 129. The addition of ABTS as a mediator had mixed effects on the decolorization of these dyes. In addition, immobilization of Lac_MM3 in an alginate matrix resulted in three-fold enhancement of enzyme reusability.