Production and localization of β-glucosidase in Trichoderma harzianum and some aspects of catabolite repression

Maximum production of aryl-β-glucosidase by Trichoderma harzianum was obtained in Vogel's medium supplemented with cellobiose as the carbon source at pH 5.0 under stationary culture conditions at 27 °C. In the exponential phase the bulk of the enzyme was almost equally distributed in the extracellular and cell debris fractions and a negligible amount was present in the cytosol. However, in the late stationary phase, extracellular β-glucosidase increased to 80% of the total enzyme. When cellulosic substrates were used, a major portion of the enzyme (90%) appeared in the extracellular fraction at all stages of growth. The repression of extracellular enzyme in the presence of exogenous glucose in the medium was apparent and the synthesis and release of enzyme were resumed after its depletion. The glucose effect in essence may be related to the adverse effect of low pH on the integrity of the enzyme.