Genetics of Ethanol-Producing Microorganisms

Abstract

Ethanol-Producing Microrganisms

A wide variety of microbial species are known to produce ethanol as a product of carbohydrate fermentation.¹ Organisms which have received attention in recent studies include a wide range of yeasts, some molds, and a number of specialized bacteria (Table 1). Traditionally, yeasts, particularly Saccharomyces cerevisiae, have been used for producing fermentation ethanol or alcoholic beverages in large-scale processes. In Table 1, Zymomonas mobilis, the predominant organism in fermentations producing Mexican “pulque” or palm wine,³⁴-⁴⁶ is the only bacterium of current economic significance. However, the development of interest in other species with the ability, for example, to convert xylose to ethanol or to ferment at high temperatures indicates that no existing strain of Saccharomyces or Zymomonas meets the specifications for all current and future uses. Certainly the use of alternative organisms, or even mixed cultures,⁴²⁴⁵ warrants investigation. However, this review will concentrate on proven ethanol producers (i.e., yeasts, particularly Saccharomyces spp., and Z. mobilis) and how these might be improved in a systematic way for ethanol production, using the wide range of genetic techniques which is now available.