Improving Biomass Sugar Utilization by Engineered Saccharomyces cerevisiae

Abstract

The efficient utilization of all available sugars in lignocellulosic bio- mass, which is more abundant than available commodity crops and starch, represents one of the most difficult technological challenges for the production of bioethanol. The well-studied yeast Saccharomyces cerevisiae has played a tradi- tional and major role in industrial bioethanol production due to its high fermentation efficiency. Although S. cerevisiae can effectively convert hexose sugars, such as glucose, mannose, and galactose, into ethanol, it is limited to utilize pentose sugars, including xylose and arabinose, leading to low ethanol yields from lignocellulosic biomass. Numerous approaches for enhancing the conversion of pentose sugars to ethanol have been examined, particularly those involving meta- bolically engineered S. cerevisiae. In this chapter, recent progress in several promising strategies, including genetic recombination of xylose reductase, xylitol dehydrogenase, and xylose isomerase, genetic engineering and evolutionary engi- neering, characterization of xylose transporters, and approaches toward understand- ing of molecular mechanisms for xylose utilization are discussed, with particular focus on xylose-utilizing strains of engineered S. cerevisiae.