One of the limiting factors for the application of Trichoderma reesei to degrade cellulosic biomass is its low β-glucosidase activity, required to convert cellobiose to glucose. The egl3 and the xyn3 promoters were used to express β-glucosidase 1 gene bgl1 through homologous recombination to improve the cellulose degradation ability of T. reesei. The recombinant strains expressing β-glucosidase 1 (BGLI) under the control of either the egl3 or the xyn3 promoter had 4.0 and 7.5 fold higher β-glucosidase activity than the native strain, which compares well to the finding that in wild-type T. reesei PC-3-7, the levels of egl3 and xyn3 mRNA expression were 6.0 and 12 fold higher respectively than that of bgl1. Matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry analysis of proteins secreted by the recombinant strains demonstrated that BGLI was overproduced. The increase in the transcription of bgl1 and the concomitant elevated level of BGLI in these recombinant strains were sufficient to degrade the cellobiose and cellotriose formed during the degradation of pretreated cedar powder.

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