Non-Saccharomyces (and Bacteria) Yeasts That Produce Ethanol

Abstract

In excess of a thousand unique yeast species have been identified, and many of them have been characterized (to a lesser or greater extent). Ninety percent (and more) of the fermentation ethanol produced globally employs species of the genus Saccharomyces (predominantly S. cerevisiae and S. pastorianus). However, there are a number of non-Saccharomyces yeast species that can produce ethanol (also called nonconventional yeast species). Nonconventional yeasts are a large and barely exploited resource of yeast biodiversity. Many of these nonconventional yeast species exhibit industrially relevant traits such as an ability to utilize complex substrates, nutrient tolerance against stresses and fermentation inhibition. The evolution of most of these yeast species was independent of Saccharomyces spp. Many of them possess novel and unique mechanisms that are not present in Saccharomyces yeasts. Most of them have been characterized as spoilage yeasts because they have been isolated from contaminated foods and beverages. Yeast species that are included in this category are Schizosaccharomyces pombe, Kluyveromyces marxianus, Schwanniomyces occidentalis, Brettanomyces bruxcellensis, Pichia stipitis, Pachysolen tannophilus and Torulaspora delbrueckii.