Systematic optimization of cellulases production and extraction by Sporotrichum thermophile mutant strain TH3-9 and application in enzymatic hydrolysis of corn stover

Abstract

Enzymatic hydrolysis of cellulose generally occurs at 40-50 ℃, which can result in slow hydrolysis rate, low sugar yield with incomplete hydrolysis and easy microbial contamination. The limitations can be resolved by adopting cellulases from thermophilic microorganisms. In this work, response surface methodology was used for optimizing cellulases production and extraction by Sporotrichum thermophile mutant strain TH3-9 in solid state fermentation. Results indicated that ammonium sulphate, initial pH and inoculum amount had significant effects on cellulases production. Maximal cellulases activities (endoglucanase activity, 718.03 U/g; filter paper activity, 126.51 U/g; β-glucosidase activity, 444.33 U/g) could be obtained by adopting corn stover (10.0g) and wheat bran (5.0g) as substrates, ammonium sulphate 1.63g, initial pH 5.1 and inoculum amount 13.8% (v/w). Compared with cellulases activities in the initial conditions, optimization resulted in 5.86-fold, 4.29-fold and 6.06-fold increase for endoglucanase activity, filter paper activity and β-glucosidase activity, respectively. During optimization of cellulases extraction, filter paper activity (FPA) was used as the response and results indicated that variables including volume of solvent, rotation speed and time had significant effects on FPA of the crude cellulases solution. Maximal FPA (24.53U/mL) could be obtained while extraction was performed at 30 ℃, 135rpm for 38min with the use of distill water as solvent. In addition, the crude cellulases solution was primarily applied in hydrolysis of alkaline hydrogen peroxide pretreated corn stover and the reducing sugar yield (418.47mg/g) could be obtained during hydrolysis at 50 ℃ for 48h.