Isolation and characterization of a novel Penicillium oxalicum strain Z1-3 with enhanced cellobiohydrolase production using cellulase-hydrolyzed sugarcane bagasse as carbon source

•Cellulase-hydrolyzed sugarcane bagasse was first used to screen for fungal cellulase.•P. oxalicum Z1-3 producing enhanced cellobiohydrolase was isolated and identified.•P. oxalicum Z1-3 produced high filter paper cellulase activity at 2.74 FPU/ml.•P. oxalicum Z1-3 hydrolyzed 92.5% of KOH-pretreated sugarcane bagasse.

Biofuels from lignocellulosic biomass are acknowledged to be a promising alternative to fossil fuels. During biomass saccharification, nearly complete conversion is rarely achieved due to the recalcitrance of the residual biomass to enzymatic hydrolysis. Few studies have examined schemes for searching for novel fungal strains that could improve the conversion. In the current study, for the first time, we searched for efficient fungal producers of cellulases in a natural decay system, using a screening process containing cellulase-hydrolyzed sugarcane bagasse as carbon source. Three hundred and seventy-three fungal strains were isolated from 69 samples collected in Guangxi Zhuang Autonomous Region, China. Twelve of the 373 strains produced more than 0.5 filter paper units (FPU)/mL and were identified as Penicillium oxalicum strains. Among them, P. oxalicum Z1-3 yielded the highest cellulase production at 2.74 FPU/ml, especially cellobiohydrolase, leading to about 0.5–2.0-fold higher synergistic enzyme activities including sugarcane bagasse residue cellulase, potassium hydroxide (KOH)-pretreated sugarcane bagasse cellulase, filter paper cellulase (FPase) and Avicelase, than the four isolates which yielded higher or similar FPase activities in comparison with the P. oxalicum reference strain HP7-1. Furthermore, a crude enzyme solution of Z1-3 was able to hydrolyze 92.5% of KOH-pretreated sugarcane bagasse to glucose within 96 h. It was also shown that the cellobiohydrolase genes of Z1-3 and their promoter regions were the same as those of the reference strain HP7-1. Altogether, this scheme, which used recalcitrant biomass residues after cellulase hydrolysis, is feasible for searching for efficient cellulase producers. This work demonstrates the great potential of P. oxalicum Z1-3 in future biotechnological applications of lignocellulosic biomass collected from industry and agriculture.