Abstract: Three cellulase-producing strains were screened from the soil sample and identified by Congo red method. A strain with the most powerful capability of producing β-glucosidase was also explored. The strain was identified as Aspergillus oryzae by morphological and ITS sequence analysis, and named as giF-10. Aspergillus oryzae giF-10 was fermented in shaking flask to obtain a great deal of β-glucosidase. Crude enzyme was purified by ammonium sulfate precipitation, Sephadex G-100 gel chromatography, and DEAE cellulose ion exchange chromatography. The specific activity of purified β-glucosidase was 40.84 U/mg. Molecular weight of β-glucosidase was approximately 90 kD as identified by SDS-PAGE. Its optimal temperature and pH were 55 ℃ and 4.5, respectively. It was stable at 30—50 ℃ and pH 4.0— 6.0. Different metal ions revealed different effects on β-glucosidase activity. Mn2+ could activate β-glucosidase while Fe3+ and Cu2+ could inhibit β-glucosidase. The enzyme showed stronger substrate specificity to salicin and cellobiose. Its Km for salicin and cellobiose were 0.676 mmol/L and 2.906 mmol/L, respectively.

Key words: Aspergillus oryzae, β-glucosidase, purification, enzymatic characteristics