THE BGL1 GENE OF TRICHODERMA-REESEI QM-9414 ENCODES AN EXTRACELLULAR,CELLULOSE-INDUCIBLE BETA-GLUCOSIDASE INVOLVED IN CELLULASE INDUCTION BY SOPHOROSE

We have investigated the effect of disruption of the bgl1-(beta-glucos idase I-encoding) gene of Trichoderma reesei on the formation of other beta-glucosidase activities and on the induction of cellulases. To th is end the bgl1 locus was disrupted by insertion of the Aspergillus ni dulans amdS (acetamidase-encoding) gene. The bgl1-disrupted strain did not produce the 75 kDa extracellular beta-glucosidase on cellulose or lactose, but still formed beta-glucosidase activity on glucose, cello biose, xylan or beta-1,3-glucan, suggesting that the enzyme(s) exhibit ing this beta-glucosidase activity is (are) not encoded by bgl1. The c ellulase-inducer sophorose induced the bgl1-encoded beta-glucosidase, whereas the remaining beta-glucosidase activity was induced by methyl- beta-D-glucoside. The bgl1-gene product was mainly secreted into the m edium, whereas the other beta-glucosidase activity was mainly associat ed with the cells. A bgl1-multicopy strain formed higher amounts of ce llulases than the parent strain. Nonsaturating concentrations of sopho rose efficiently induced cellobiohydrolase I formation in the bgl1-mul ticopy strain, but less efficiently in the bgl1-disrupted strain. The multicopy strain and the parent strain were comparably efficient at sa turating sophorose concentrations. The beta-glucosidase inhibitor noji rimycin strongly inhibited induction in all strains. These data sugges t that the bgl1-encoded beta-glucosidase is not identical to the plasm a-membrane-bound, constitutive, methyl-and glucoside inducible beta-gl ucosidase, but represents an extracellular cellulose-induced enzyme. B oth enzymes contribute to rapid induction of cellulases by modifying t he inducer sophorose.