Production of laccase as the sole phenoloxidase by a Brazilian strain of Pleurotus pulmonarius in solid state fermentation

The production of laccase by a Brazilian strain of Pleurotus pulmonarius was studied in solid state fermentation using wheat bran as substrate. Among oxidative and hydrolytic enzymes tested (laccase, aryl alcohol oxidase, lignin peroxidase, Mn peroxidase, xylanase and cellulase), laccase was the main enzyme produced by P. pulmonarius. The most suitable condition for maximum production of laccase (8,600 U/g substrate) was initial moisture content of 75% and 5 days of cultivation at 30 degrees C. The optimum pH and temperature for laccase activity were found to be 6.5 and 50 degrees C, respectively. P. pulmonarius laccase was stable at 50 degrees C for more than 6 hours, and it retained about 73% and 18% of its activity when heated for 1 h at 55 and 60 degrees C, respectively. The enzyme was greatly stable at alkaline pH, but not at acidic pH. The laccase activity appear to be correlated with the ability of crude extract to decolourize several industrial dyes.