Characterization of spore laccase from Bacillus subtilis WD23 and its use in dye decolorization

Abstract

A bacterial strain, designated as WD23, was isolated from the forest soil using M9 medium supplemented with 0.4 mmol/L Cu²⁺. The spores from this strain showed laccase-like activity, oxidizing syringaldazine, 2,6-dimethoxyphenol and 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulfonate acid) (ABTS). The strain was identified as Bacillus subtilis based on its morphological and physiological properties, and 16S rDNA sequence analysis. The optimum pH and temperature for the spore-bound laccase were 6.8 and 60°C, respectively. The temperature half-life of the laccase was 2.5 h at 80°C and 68 h at 60°C. It also showed high stabilities over a broad pH range. The pH half-life of the laccase was more than 6 months at pH 6.8. The sensitivities of the laccase to organic solvents and inhibitors were tested and it was found that laccase activity was strongly inhibited by methanol, EDTA and dithiothreitol, but only slightly affected by NaN₃ and xylene. The spore enzyme efficiently decolorized anthraquinone and azo dyes in 24 h.

Key words: Bacterial laccase, spore, characteristics, Bacillus subtilis, dye decolorization.