Partial purification and characterization of the novel halotolerant and alkalophilic laccase produced by a new isolate of Bacillus subtilis LP2

Abstract

Laccases (benzenediol: oxygen oxidoreductases, [EC1.10.3.2] are mostly known as members of the blue multicopper oxidase family that are used in very different industrial applications: textile, pulp and paper, food, cosmetics industries, bioremediation process, biosensor, biofuel and organic synthesis. Stability against the extreme conditions is an important property and it makes laccase suitable for several industrial processes. Laccase should have salt resistance to be used in textile dye degradation because the textile wastewaters include dyes with high concentrations of salts, especially NaCl. Bacterial laccases are preferable to be used for bioremediation process due to their high stability to extremely salt contaminated and alkalophilic environment. Bacillus subtilis LP2 was identified as a source of alkali-tolerant, salt resistant laccase. Laccase showed activity over a wide pH (4-10) and temperature (30-80 degrees C) range. Maximum laccase activity was observed as 140.4U/mg (umol/min*mg) at pH 8 and 50 degrees C with the substrate guaiacol. Stability of laccase was determined as 60% and 20% after incubation of the enzyme for different time intervals of 20 and 40min at 50 degrees C and pH 8. SDS (10mM) and EDTA (5mM) decreased laccase activity from 100% to 0% and 56%, respectively. Despite the other inhibitors, NaCI increased the activity of laccase to 167% at 500mM concentration. Laccase from Bacillus subtilis LP2 barely showed the activity on the substrates vanillin and L-tyrosine. These results clearly show that laccase from Bacillus subtilis LP2 has high potential to be used for several applications in textile industry.