which also contributes
to the reduction of bacterial contaminants as claimed in the
patent of Narendranath et al. (2000). Other yeasts, as
Schizosaccharomyces pombe, present the additional advantage
of tolerating high osmotic pressures (high amounts of
salts) and high solids content (Bullock, 2002; Goyes and
Bolan˜os, 2005). In fact, a fermentation process using a wild
strain of this yeast has been patented (Carrascosa, 2006).
Among bacteria, the most promising microorganism is
Zymomonas mobilis, which has a low energy efficiency
resulting in a higher ethanol yield (up to 97% of theoretical
maximum). However, its range of fermentable substrates is
too narrow (glucose, fructose and sucrose) (Claassen et al.,
1999). Other disadvantage of the use of this bacterium during
the fermentation of sugar cane syrup and other sucrosebased
media is the formation of the polysaccharide levan
(made up of fructose units), which increases the viscosity
of fermentation broth, and of sorbitol, a product of fructose
reduction that decreases the efficiency of the conversion
of sucrose into ethanol (Lee and Huang, 2000).