Assessments on the catalytic and kinetic properties of beta-glucosidase isolated from a highly efficient antagonistic fungus Trichoderma harzianum

Abstract

Due to the toxicity and inefficiency of chemical fungicides to control infestation of Macrophomina phaseolina (Tassi) Goid which causes charcoal rot in plants, a biotechnological approach using β-glucosidase (EC.3.2.1) as the alternative bioactive ingredient in fungicide is hereby, proposed. The extracellular enzyme was isolated from a highly efficient fungal antagonist, Trichoderma harzianum T12. The highly similar molecular masses obtained using SDS-PAGE (96 kDa) and MALDI-TOF mass spectrometry (98.3 kDa) affirmed that the β-glucosidase was purified to homogeneity. Consequently, optimum catalytic parameters that rendered the highest enzyme activity were found to be: 45ËšC, pH 7, inoculum size of 10 % (w/v), supplementation with metal ions Zn²⁺ and Mn²⁺ ions, and Tween 80. Addition of wheat bran and (NH₄)₂SO₄ as carbon and nitrogen sources also improved enzyme activity. BLASTn showed the sequence of β-glucosidase T12 was highly identical to other β-glucosidases viz. T. harzianum strain IOC-3844 (99%), T. gamsii and T. virens bgl1 (86 %) as well as T. reesei strain SJVTR and T. viride strain AS 3.3711 (84 %). Kinetic assessment showed that β-glucosidase T12 catalyzes hydrolytic activity is characterized by a K_m of 0.79 mM and V_max of 8.45 mM min^-1 mg^-1 protein, with a corresponding k_cat of 10.69 s^-1.