Co-fermentation of cellulose/xylan using engineered industrial yeast strain OC-2 displaying both β-glucosidase and β-xylosidase.

We constructed a recombinant industrial Saccharomyces cerevisiae yeast strain OC2-AXYL2-ABGL2-Xyl2 by inserting two copies of the β-glucosidase (BGL) and β-xylosidase (XYL) genes, and a gene cassette for xylose assimilation in the genome of yeast strain OC-2HUT. Both BGL and XYL were expressed on the yeast cell surface with high enzyme activities. Using OC2-AXYL2-ABGL2-Xyl2, we performed ethanol fermentation from a mixture of powdered cellulose (KC-flock) and Birchwood xylan, with the additional supplementation of a 30-g/l Trichoderma reesei cellulase complex mixture. The ethanol yield (gram per gram of added cellulases) of the strain OC2-AXYL2-ABGL2-Xyl2 increased approximately 2.5-fold compared to that of strain OC2-Xyl2, which lacked β-glucosidase and β-xylosidase activities. Notably, the concentration of additional T. reesei cellulase was reduced from 30 to 24 g/l without affecting ethanol production. The BGL- and XYL-displaying industrial yeast of the strain OC2-AXYL2-ABGL2-Xyl2 represents a promising yeast for reducing cellulase consumption of ethanol fermentation from lignocellulosic biomass by compensating for the inherent weak BGL and XYL activities of T. reesei cellulase complexes.