Co-expression of Endoxylanase and Endoglucanase in Scheffersomyces stipitis and Its Application in Ethanol Production

Scheffersomyces stipitis strain BCC15191 is considered as a biotechnologically valuable yeast for its ability to ferment glucose and xylose, the main sugar components in plant biomass, to ethanol. However, the wild strain lacks of endogenous cellulases and hemicellulases that limited biomass utilization. In order to improve biomass degrading ability of S. stipitis BCC15191, new integrative plasmids harboring constitutive TEF1 promoter and codon-optimized zeocin or hygromycin antibiotic resistance genes were developed. Aspergillus niger endoxylanase and Aspergillus aculeatus endoglucanase activities were demonstrated in transformant cells expressing codon-optimized genes. S. stipitis co-expressing endoxylanase and endoglucanase was able to grow in medium containing xylan and beta-glucan as carbon sources and directly produced ethanol with yields of 2.7 g/L. It could also use pretreated corncob as a carbon source for ethanol production. These results suggested that recombinant S. stipilis is possible for consolidated bioprocessing of biomass.