Screening and Identification of β-Glucosidase-Producing Fungi,and Purification and Enzymatic Analysis

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.