Hemicellulose Degradation and Utilization by a Synthetic Saccharomyces cerevisiae Consortium

Abstract

Since Saccharomyces cerevisiae does not inherently possess the capability to utilize pentose sugars released from hemicellulose degradation, the degradation and utilization of hemicellulose poses a conundrum to bioethanol production by consolidated bioprocessing (CBP) using S. cerevisiae. In this study, S. cerevisiae was exploited for its ability to degrade xylan, one of the major polysaccharide chains present in hemicellulose. Different hemicellulases from Trichoderma reesei, namely: endoxylanase (Xyn2), {beta}-xylosidase (Bxl1), acetylxylan esterase (Axe1), -D-glucuronidase (Glr1) and -L-arabinofuranosidase (Abf1), were heterologously secreted by S. cerevisiae. A mixture experimental design was adapted to statistically describe the synergistic interactions between the hemicellulases and to determine the optimum formulations for the hydrolysis of xylan substrates. The hydrolytic activities of the hemicellulase mixtures were then improved by displaying the hemicellulases on the yeast surface to serve as whole-cell biocatalysts. The engineered yeast strains displaying hemicellulases were further engineered with xylose-utilization genes to enable abilities of utilizing xylose as a sole carbon source. The resulting consortia were then able to grow and produce ethanol from different xylan substrates.