Metabolic Engineering of Saccharomyces cerevisiae for Conversion of d -Glucose to Xylitol and Other Five-Carbon Sugars and Sugar Alcohols

Abstract

ABSTRACT Recombinant Saccharomyces cerevisiae strains that produce the sugar alcohols xylitol and ribitol and the pentose sugar d -ribose from d -glucose in a single fermentation step are described. A transketolase-deficient S. cerevisiae strain accumulated d -xylulose 5-phosphate intracellularly and released ribitol and pentose sugars ( d -ribose, d -ribulose, and d -xylulose) into the growth medium. Expression of the xylitol dehydrogenase-encoding gene XYL2 of Pichia stipitis in the transketolase-deficient strain resulted in an 8.5-fold enhancement of the total amount of the excreted sugar alcohols ribitol and xylitol. The additional introduction of the 2-deoxy-glucose 6-phosphate phosphatase-encoding gene DOG1 into the transketolase-deficient strain expressing the XYL2 gene resulted in a further 1.6-fold increase in ribitol production. Finally, deletion of the endogenous xylulokinase-encoding gene XKS1 was necessary to increase the amount of xylitol to 50% of the 5-carbon sugar alcohols excreted.