Bioethanol Production from Xylose: Problems and Possibilities

Agricultural, industrial and urban residues are the best alternative sources for bioethanol production. Technology for efficient utilisation of lignocellulose wastes relies on utilisation of both the cellulosic as well as hemicellulosic portions of the biomass. After hydrolysis, glucose and xylose are produced from cellulose and hemicellulose, respectively, as the major sugars in the hydrolysate. Xylose is the second most abundant sugar present in the plant biomass. Utilisation of xylose along with glucose is required from an industrial prospective. Although yeasts are more resistant to ethanol than bacteria, low ethanol tolerance of xylose-fermenting yeasts is a main limiting factor for industrial ethanol production. Metabolic engineering has so far been unsuccessful to provide satisfactory results, and one of the major reasons is the lack of consideration of various environmental factors, which play critical role during xylose fermentation. This review paper focuses on various environmental factors along with the metabolic engineering of xylose-fermenting yeasts to improve ethanol production from xylose.