Construction of a recombinant Trichoderma reesei strain expressing Aspergillus aculeatus β‐glucosidase 1 for efficient biomass conversion

To develop a Trichoderma reesei strain appropriate for the saccharification of pretreated cellulosic biomass, a recombinant T . reesei strain, X3AB1, was constructed that expressed an Aspergillus aculeatus β‐glucosidase 1 with high specific activity under the control of the xyn3 promoter. The culture supernatant from T . reesei X3AB1 grown on 1% Avicel as a carbon source had 63‐ and 25‐fold higher β‐glucosidase activity against cellobiose compared to that of the parent strain PC‐3‐7 and that of the T . reesei recombinant strain expressing an endogenous β‐glucosidase I, respectively. Further, the xylanase activity was 30% lower than that of PC‐3‐7 due to the absence of xyn3 . X3AB1 grown on 1% Avicel‐0.5% xylan medium produced 2.3‐ and 3.3‐fold more xylanase and β‐xylosidase, respectively, than X3AB1 grown on 1% Avicel. The supernatant from X3AB1 grown on Avicel and xylan saccharified NaOH‐pretreated rice straw efficiently at a low enzyme dose, indicating that the strain has good potential for use in cellulosic biomass conversion processes. Biotechnol. Bioeng. 2012;109: 92–99. © 2011 Wiley Periodicals, Inc.