Production of Highly Thermostable Laccase from Penicillium spinulosum for Enhanced Delignification of Untreated Wheat Bran

Lignin confers rigidity on plant cell wall and poses a challenge to hydrolysis of cellulose, which makes production of biofuels from lignocellulose an overwhelming problem. This prompts continuous search for novel ligninolytic enzymes, especially, laccases for delignification of lignocellulose for improved saccharification of biomass. This study reports production, physicochemical properties and delignification efficiency of laccases from Penicillium and Trichoderma species on untreated wheat bran. Fungal laccases were produced using different agroresidues (wheat bran, coconut shell and palm kernel shell) as substrates in submerged fermentation. Best substrate for laccase production was determined. Physicochemical properties of crude enzymes and delignification efficiency of the laccases were determined on untreated wheat bran using pure laccase as control. Wheat bran supported maximum laccase production from fungi under study. Highest laccase yield of 22.5 U/mL was obtained from P. spinulosum. Laccase from P. spinulosum was optimally active at pH 7.0 and 50 °C and exhibited remarkable high thermostability with 61.6% residual activity at 90 °C after 2 h incubation. The activity of the thermostable enzyme was enhanced in the presence of Cu2+. Biodelignification efficiency of cell-free extract from P. spinulosum, T. koningii, and P. restrictum on wheat bran were 95%, 81.5% and 63.5%, respectively. Surprisingly, a much lower delignification efficiency of 33.42% was obtained with commercial laccase from Trametes versicolor. The high thermostability and striking delignification efficiency of laccase from P. spinulosum make the enzyme a good bioresource for biodelignification of untreated lignocellulose for biofuel production.