earticle

영어

Efficient conversion of cellulosic biomass to ethanol requires utilization of both hexoses (C-6 sugar) and pentoses (C-5 sugar), primarily glucose and xylose. Saccharomyces cerevisiae which has been used for ethanol production from starch and sugarcane cannot convert xylose to ethanol because the yeast does not have a xylose metabolizing activity. S. cerevisiae was metabolically engineered for converting xylose to ethanol by introducing xylose reductase (XR) and xylitol dehydrogenase (XDH) from Pichia stipitis, a natural xylose metabolizing yeast. Even with metabolic engineering of S. cerevisiae, the recombinant S. cerevisiae cannot utilize xylose as efficiently as glucose due to competitive transport of xylose and glucose for the hexose transport system. S. cerevisiae has transporters (proteins responsible for sugar transport) with high affinity for glucose relative to xylose and hence xylose transport is strongly inhibited by the presence of glucose in the fermentation broth. A fermentation strategy has to be designed by taking into account competitive transport between xylose and glucose for the hexose transporters in S. cerevisiae. This presentation will cover metabolic engineering of the xylose assimilation pathway and optimization of a fermentation process in an attempt to improve ethanol productivity from cellulosic biomass.