Saccharomyces spp. are the safest and most effective micro-
organisms for fermenting sugars to ethanol and traditionally
have been used in industry to ferment glucose (or hexose
sugar)-based agricultural products to ethanol. Cellulosic bio-
mass, which includes agriculture residues, paper wastes, wood
chips, etc., is an ideal inexpensive, renewable, abundantly avail-
able source of sugars for fermentation to ethanol, particularly
ethanol used as a liquid fuel for transportation. However, Sac-
charomyces spp. have been found to be unsuitable for ferment-
ing sugars derived from cellulosic biomass. This is because
most of the hydrolysates of cellulosic biomass contain two
major fermentable sugars, glucose and xylose. Saccharomyces
spp., including Saccharomyces cerevisiae, are not able to fer-
ment xylose to ethanol or to use this pentose sugar for aerobic
growth