Genetic improvement of xylose utilization by saccharomyces cerevisiae

Abstract

It is estimated that capital costs associated with lignocellulosic ethanol are about US $4 per gallon and that these need to be reduced by more than half to be -economically sustainable (Hahn-Hagerdal et al. 2006; Gray et al. 2006). Complete substrate utilization is one of the prerequisites to render lignocellulosic ethanol processes economically competitive. This means that all types of sugars in cellulose must be converted to ethanol, and that microorganisms must be obtained that efficiently perform this conversion under industrial conditions. Biomass is composed of cellulose (40-50%), hemicellulose (25-35%), and lignin (15-20%) (Ragauskas et al. 2006; Lin and Tanaka 2006). Glucose constitutes about 60% of the total sugars available in cellulosic biomaterial. Fermentation of the available sugars in cellulosic biomass presents a unique challenge because of the presence of other sugars such as xylose and arabinose (C5 sugars). The degree of branching and identity of the minor sugars in hemicelluloses tends to vary depending upon the type of plant. The conversion of biomass to useable energy is, however, not economical, unless hemicellulose is used in addition to cellulose. © 2011 Springer Science+Business Media, LLC.