Functional Characterization of Laccase Isozyme (PoLcc1) from the Edible Mushroom Pleurotus ostreatus Involved in Lignin Degradation in Cotton Straw

Fungal laccases play important roles in the degradation of lignocellulose. In this study, the laccase producing cotton straw medium for Pleurotus ostreatus was optimized by single-factor and orthogonal experiments, and to investigate the role of Lacc1 gene, one of the laccase-encoding genes, in the degradation of cotton straw lignin, an overexpression strain of Lacc1 gene was constructed, which was analyzed for the characteristics of lignin degradation. The results demonstrated that the culture conditions with the highest lignin degradation efficiency of the P. ostreatus were the cotton straw particle size of 0.75 mm, a solid–liquid ratio of 1:3 and containing 0.25 g/L of Tween in the medium, as well as an incubation temperature of 26 °C. Two overexpression strains (OE L1-1 and OE L1-4) of Lacc1 gene were obtained, and the gene expression increased 12.08- and 33.04-fold, respectively. The results of (1)H-NMR and FTIR analyses of significant changes in lignin structure revealed that Lacc1 gene accelerated the degradation of lignin G-units and involved in the cleavage of β-O-4 linkages and the demethylation of lignin units. These findings will help to improve the efficiency of biodelignification and expand our understanding of its mechanism.