Extracellular Alkaline Thermostable Laccase from Micrococcus species: Partial Purification and Characterization

A bacterial strain producing extracellular alkaline thermostable laccase has been isolated from sawdust effluents and identified as Micrococcus species. The laccase was partially purified and characterized. The isolate showed maximum laccase production after 120 h, at 30ºC with an optimum pH of 9.0. The specific activity was 127.94 U/mg with a purification fold of 5.54 was obtained with DEAE-cellulose anion exchange chromatography. The molecular weight of purified laccase was 23 kDa. A temperature of 40ºC and pH of 9.0 was found to be optimum for laccase activity. Laccase was stable at 50ºC and at a pH of 9.0 after 1 h incubation. Laccase retained 70-80% of its activity in the presence of 5% DMSO, butanol, acetone and isopropanol. The laccase activity was inhibited by 10 mM SDS (90%), mercuric chloride (80%) and p-CMB (80%). However, only 30% of the enzyme activity was inhibited by sodium azide and EDTA. The characteristics of partially purified laccase with respect to inhibitors and metal ions contribute towards the understanding for the use of bacterial laccases for industrial applications.