Recombinant expression, activity screening and functional characterization identifies three novel...

The hydrolysis of cellulose into fermentable sugars is a costly and rate-limiting step in the production of biofuels from renewable feedstocks. Developing new cellulase systems capable of increased cellulose hydrolysis rates would reduce biofuel production costs. With this in mind, we screened 55 fungal endoglucanases for their abilities to be expressed at high levels by Aspergillus niger and to hydrolyze amorphous cellulose at rates significantly greater than that obtained with TrCel5A, one of the major endoglucanases in the Trichoderma reesei cellulase system. This screen identified three endoglucanases, Aureobasidium pullulans ApCel5A, Gloeophyllum trabeum GtCel12A and Sporotrichum thermophile StCel5A. We determined that A. niger expressed the three endoglucanases at relatively high levels (≥0.3 g/l) and that the hydrolysis rate of ApCel5A and StCel5A with carboxymethylcellulose 4M as substrate was five and two times greater than the T. reesei Cel5A. The ApCel5A, GtCel12A and StCel5A enzymes also demonstrated significant synergy with Cel7A/CbhI, the major exoglucanase in the T. reesei cellulase system. The three endoglucanases characterized in this study are, therefore, promising candidate endoglucanases for developing new cellulase systems with increased rates of cellulose saccharification.