Expression of Aspergillus aculeatus β-Glucosidase I Gene in Pichia pastoris and Its Application on the Synthsis of Alkyl Glucoside

beta-Glucosidases, as a specific group of glycosyl hydrolase could catalyze the hydrolysis of beta-1, 4-glycosidic bond presented in short-chain oligosaccharides(containing 2-6 monosaccharides), are widely used in the degradation of cellulose, the improvement of food flavor and so on. The gene of Aspergillus aculeatus NO. F-50 beta-glucosidase I was cloned and integrated into Pichia pastors GS115, in which beta-glucosidase I can be expressed and secreted in an active form. The recombinant beta-glucosidase I had an optimum pH of 5.0 and an optimum temperature of 65 degrees C using 4-nitrophenyl-beta-D-glucopyranoside (pNPG) as substrate. The highest hydrolytic activity and protein expression level at 50 degrees C in the culture supernatant of recombinant strain were up to 33.8 U/mL and 0.388 mg/mL, respectively. The recombinant beta-glucosidase I was found to be able to catalyze the synthesis of alkyl glucoside through reverse-hydrolysis or trans-glycosylation reaction. Some major influential factors in water/organic two-phase system such as pH value, water content, overall concentration of glucose and enzyme concentration were optimized. The yield of butyl glucoside, hexyl glucoside, octyl glucoside and decyl glucoside was 51.4%, 28.8%, 6.9% and 3.0%, respectivly.