Biodegradation of crystal violet mediated by CotA from Bacillus amyloliquefaciens

Triphenylmethane dyes are commonly used in dyeing and printing, but such dyes are recalcitrant to degradation and thus biodegradation of dye compounds has received increasing attention. Here, a recombinant bacterial laccase, CotA, from Bacillus amyloliquefaciens MN-13 was expressed in Escherichia coli BL21(DE3) and used as a biocatalyst to degrade crystal violet (CV). The recombinant CotA remained stable at temperatures in the range 30-40 °C and retained 44-100% enzyme activity at pH 4.5-8.0. The CotA exhibited high activities for decolorization of CV and, after 72 h of incubation, CotA decolorized 70.98% of CV at pH 5.0 and 30 °C. In the UV-visible spectra of CV solution treated by CotA, the full wavelength scan indicated that the chromophore of the triphenylmethane structure of CV was destroyed and CV was degraded into small-molecule aromatic compounds. The main degradation compounds of CV were identified as bis[4-(dimethylamino) phenyl] methanone and its N-demethylation derivative by HPLC/MS/MS. Based on these data, a hypothetical degradation pathway of CV by CotA, including N-demethylation and cleavage of the chromophore structure initiated by radicals, is proposed.