Isolation, identification of a laccase-producing bacterial strain and enzymatic properties of the laccase

Abstract:

[Objective] The aim of this study was to screen laccase-producing bacterial strains and to investigate the enzymatic properties as well as decolorization ability of the laccase. [Methods] Enrichment medium supplemented with copper ions was used to isolate bacterial strains exhibiting laccase activity. The isolated strain was identified by morphology observation, physiological and biochemical tests and 16S rDNA sequence analysis. The enzymatic properties of laccase were investigated with syringaldazine as substrate. Dye decolorization ability of the laccase was tested by determining the change at maximum wavelength of synthetic dyes. [Results] A bacterial strain LS05 with high laccase activity was isolated from forest soil, and was identified as Bacillus amyloliquefaciens. The spore laccase of strain LS05 demonstrated optimum pH and temperature at pH 6.6 and 70 °C, respectively. It also showed high stability, retaining its activity after incubation at 70 °C for 10 h or at pH 9.0 for 10 d. Resistance towards SDS and EDTA was found for the spore laccase. The enzyme could efficiently decolorize different synthetic dyes at alkaline conditions. More than 93% of remazol brilliant blue R, reactive black 5 and indigo carmine were decolorized within 1 h. [Conclusion] The spore laccase of Bacillus amyloliquefaciens LS05 was highly stable at high temperature and alkaline pH, which was more advantageous in industrial application than fungal laccase. It showed high potential in treatment of industrial dye effluents.