Copper induction of laccases by Lentinus polychrous under liquid-state fermentation

The fungus Lentinus polychrous, an edible mushroom popular in Northeast Thailand secretes ligninolytic enzymes, mainly laccases and manganese peroxidases. This research investigates the production of ligninolytic enzymes by the fungus culture in liquid medium in the presence of two well-known laccase inducers. Using Basidiomecetes synthetic medium (BSM), higher laccase activity of 350 U L−1 was obtained at day 14, when the culture was induced in the presence of 1.0 mM CuSO4, but not with 1.0 mM 2,5-xylidine. Higher concentration (3.0 mM) CuSO4 could inhibit enzyme production and the fungal growth. Optimum inducer concentration for laccase production by L. polychrous was 0.1 mM CuSO4, which yielded the highest laccase activity per biomass (67.9 U g−1). When the fungus was cultured in Erlenmeyer flasks in Glucose Yeast Peptone (GYP) medium, the maximum production of laccase was found to be approximately 2000 U L−1 with 0.3 mM CuSO4 as inducer for 2 weeks. Laccase production in a bioreactor yielded more than 1000 U L−1 laccase at 8 days culture, making this system feasible for enhancement of high laccase production.