β-Glucosidase excretion in Trichoderma strains with different cell wall bound β-1,3-glucanase activities
Two different strains of Trichoderma pseudokoningii (SE1 A8 and SE1 D81) and Trichoderma viride QM 9123 release into the medium different proportions of the total β-glucosidase activity produced. This observation correlates with the degree of β-1,3-glucanase binding to the cell wall found for each strain. DEAE-Sephadex ion-exchange chromatography revealed three peaks of β-1,3-glucanase activity. These three enzymes (enzyme I, enzyme II, and enzyme III) differ in their extent of binding to the cell walls, their activity on isolated cell walls and Trichoderma β-glucan, and their affinity for β-glucan. Of these enzymes, enzyme II shows the largest variation in relative importance among the three strains and is located predominantly within the mural compartment. Enzyme II has the highest activity on and affinity for Trichoderma β-glucan. Enzyme II is also the most active in releasing β-glucosidase from cell walls of strain SE1 A8 (the strain excreting a high proportion of its β-glucosidase into the culture fluid) as well as from strain SE1 D81 (little β-glucosidase activity in the culture fluid). It is concluded that the action of β-1,3-glucanase II on cell wall β-glucan may be responsible for the in vivo release of cell wall bound β-glucosidase into the culture fluid.