New route of lignocellulosic biomass sugars fermentation to ethanol by native Saccharomyces cerevisiae

Fuel ethanol, which is currently produced from food-based sugars, can also be produced via fermentation of sugars derived from lignocellulosic biomass. Lignocellulosic biomass is an abundant, less expensive feedstock. The fermentation of xylose is essential for the cost-effective bioconversion of lignocellulose to fuels and chemicals, but wild-type strains of Saccharomyces cerevisiae do not metabolize xylose because the metabolic pathways convert xylose to xylitol via an NADPH-linked xylose reductase. Fermentation of xylose to ethanol through xylulose does occur in organisms which possess an NADH-linked aldose reductase, indicating that a balanced supply of NADP and NADPH must be maintained to avoid xylitol production. Conversion of xylose to xylulose in high yield and at low cost from biomass hydrolysate has the potential to bypass the barrier to ethanol production from C5 and C6 sugars with native yeast. We have previously developed a reactive-extraction based method for high yield conversion of xylose to xylulose. We present here the results of xylulose and xylulose/glucose mixed sugar fermentations to ethanol by native S. cerevisiae.