Pachysolen tannophilus: Properties and process considerations for ethanol production from d-xylose

Abstract

d-Xylose comprises nearly one-third of the reducing sugars obtained from lignocellulose hydrolysis. Despite its relative abundance in crop and forest residues, xylose has been found unfermentable by most yeasts. A process for efficient xylose fermentation is expected to have significant impact on the future economics of converting lignocellulose to ethanol and may also provide additional profit for existing wood processing industries releasing xylose-rich waste streams, i.e. paper mills producing sulphite liquor . Pachysolen tannophilus was the first yeast discovered capable of significant ethanol production from xylose and has served as a model for studies of other yeasts mediating this conversion. Current knowledge about biochemical pathways involved in xylose utilization by this yeast is reviewed. Factors involved in regulating carbon flow to products are discussed in conjunction with process considerations for optimizing ethanol accumulation. Finally, the prospect of more efficient ethanol production through genetic strain improvement is considered.