Tuesday, May 3, 2011
Lignocellulosic biomass, such as wood and agricultural residues, is an attractive material for fuel ethanol production. Cellulolytic enzymes from filamentous fungi are widely employed for the hydrolysis process of pretreated biomass. However, the enzyme composition of native fungal cellulase system is not necessarily suitable for the hydrolysis of pretreated biomass. To better understand the cellulase system suitable for the hydrolysis of individual pretreated biomass, we tried to design a core cellulase mixture consisting of cellulosic enzymes from Acremonium cellulolyticus. A. cellulolyticus CF2612 is one of several promising cellulase-producing fungal strains for biomass hydrolysis. To purify the core cellulosic enzymes from CF2612, an enzyme assay was used that was based on the synergistic hydrolysis of Avicel, which is considered as a model substrate of pretreated lignocellulose. Five core cellulosic enzymes (two cellobiohydrolases: Cel6A and Cel7A; two endoglucanases: Cel5A and Cel7B; and xylanase: Xyl10A) and β-glucosidase (Bgl3A) were purified to homogeneity, characterized, and identified by LC-MS/MS analysis. Individually Cel5A, Cel7B and Xyl10A had synergistic effects with a Cel6A + Cel7A mixture for glucan hydrolysis of corn stover residue treated by dilute acid. The optimized cellulase system consisting of the four-core enzyme mixture (Cel5A, Cel6A, Cel7A and Xy10A) and Bgl3A resulted in 60% conversion of glucan in the corn stover residue with a total enzyme loading of 5.7 mg protein/g glucan. Compositional evaluation of the core cellulase system using pretreated biomass will be helpful to develop the fungal strain producing cellulase enzymes optimized for hydrolysis of the target biomass.