Induction of Laccase Production and Analysis of Laccase Isozymes in Trichophyton rubrum LKY-7

Abstract

Trichophyton rubrum LKY-7 is a wood-degrading fungus, which has been isolated from hardwood chip piles. T. rubrum LKY-7 showed better growth in glucose-peptone medium (GPM) than in basal medium (BM) with rotary shaking, and mycelial growth was facilitated by the presence of wood powder. Aeration significantly increased the production of laccase in GPM (6 to 17 U/mL), and the addition of wood powder to the medium greatly increased it to 78.5 U/mL. T. rubrum LKY-7 produced no detectable amounts of lignin peroxidase, manganese peroxidase, cellulose, or xylanase under the prescribed culture conditions. A three-step chromatographic separation of the laccase indicated that at least two kinds of laccase isozymes were produced by the fungus. Activity staining of the non-boiled enzyme samples after SDS-PAGE revealed different active protein band patterns for the laccase produced in the absence or presence of the wood powder. A difference in the isozyme pattern was also observed on the activity stained gel after native PAGE. These results suggest that wood powder not only increases the production of laccase but also changes the kinds of isozymes produced by T. rubrum LKY-7. No laccase active bands were detected when the enzyme preparations were boiled for 60 s or longer, indicating that the laccase isozymes are heat-labile.