Production and characterization of cellulolytic enzyme from Penicillium oxalicum GZ-2 and its application in lignocellulose saccharification

摘要

A large amount of FPase (1.4 U/mL), CMCase (2.0 U/mL), cellobiohydrolase (0.6 U/mL), and p-glucosidase (2.7 U/mL) activities were produced when Pemcillium oxalicum GZ-2 was grown on rice straw in a 5 L bioreactor. The zymography demonstrated that the expression abundance of cellulose-degrading proteins (35-70 kDa) responded to high cellulolytic enzymes activity. Cellobiohydrolase, exo-beta-1,3-glucanase, endo-beta-l,4-glucanase, swollenin, and other glycoside hydrolases were identified in visible hydrolyzed bands in zymogram gel using MALDI-TOF-MS/MS. The relative proportions of cellulose-degrading proteins were 50.0%, 45.7%, and 44.1% in the crude enzymes induced by wheat straw, rice straw, and corn stover, respectively. It suggested that the majority of extracellular proteins were cellulose-degrading enzymes induced by agricultural wastes. The optimized pH and temperature for CMCase and p-glucosidase activity were 3.0 at 50 ℃ and 5.0 at 60 ℃, respectively. The CMCase and p-glucosidase showed remarkable stability at pH 4.0-9.0 and 3.0-7.0 with 80% of the maximum activity, respectively. Although the FPase activity was similar, the p-glucosidase activity of P. oxalicum GZ-2 was 2.8 times greater than that of Trichoderma reesei RUT-C30. The culture supernatants of P. oxalicum GZ-2 showed more efficiently capability to enzymatic hydrolysis of Avicel and corncob compared to commercial cellulase. For the saccharification of alkali-pretreated corncob, a higher reducing sugar and glucose yield was obtained using the culture supernatants from P. oxalicum GZ-2 than those from T. reesei RUT-C30. However, the highest sugar yields obtained from the mixture of enzymes indicated that a better design cocktail was also important for hydrolyzing biomass.