Consolidated biosaccharification of corn cob by novel lignocellulolytic enzymes from Bacillus subtilis CFB-09

Consolidated biosaccharification (CBS) of lignocellulosic biomass is evolving as a strategy to overcome biomass recalcitrance and enhance bioconversion efficiency. However, low yield of enzyme cocktail from lignocellulolytic microorganisms poses a challenge to the process. It is therefore important to identify and explore microbial sources that can produce high titers of lignocellulolytic enzymes, and develop strategies for improved enzyme induction. This study investigated the lignocellulolytic enzyme system of Bacillus subtilis CFB-09 using a combination of agro-residues and pure celluloses as co-substrates under submerged fermentation. The activity of cellulases, hemicellulases, and ligninolytic enzymes in cell-free extracts was determined. The multienzyme crude extracts obtained were used to hydrolyze unpretreated corn cob and sugarcane bagasse in a modified CBS process. The results showed that B. subtilis CFB-09 produced high yields of cellulases (144.85 U mg-1 protein endoglucanase, 104.4 U mg-1 protein exoglucanase, and 793.5 U mg-1 protein beta-glucosidase) and hemicellulases (27.5 U mg-1 protein xylanase and 583 U mg-1 protein beta-xylosidase) at 48 h, as well as ligninolytic enzymes (294.25 U mg-1 protein laccase, 1110.2 U mg-1 protein lignin peroxidase, and 304.78 U mg-1 protein manganese peroxidase) at 72 h on corn cob. Consolidated biosaccharification resulted in a 3.5-fold increase in the yield of reducing sugar from corn cob (0.99 mg/mL) at pH 7.0 and 50 degrees C, above the yield obtained from sugarcane bagasse (0.28 mg mL-1). The findings indicate that B. subtilis CFB-09 could produce high yield of lignocellulolytic enzymes in a timely manner by deconstructing untreated corn cob through CBS, resulting in improved yields of reducing sugars for biofuel production.