Yeast: Nomenclature

The nomenclature of various yeasts is far from straightforward and is in the process of being revised. Taxonomists—scientists who classify and name plants and animals—have traditionally had difficulty with the various micro-organisms because early microscopes revealed little detail, and because the appearance of an organism depended on the conditions of its growth, isolation, and preparation for observation. The result has been that names have changed over time as laboratory equipment improved and as new techniques were perfected. In particular, the development of methods to study the genetic information contained in chromosomal DNA has provided more reliable ways to characterize and classify yeasts. Indeed, a Saccharomyces cerevisiae yeast was the first higher organism to have its whole genome sequenced, by 1996. Genome analysis has revealed that some yeasts which were thought to be closely related were in fact only distantly related, and vice versa. Furthermore, some characteristics of yeasts that were used to differentiate species, such as the pattern of sugars that can be fermented, were found to represent natural variation within that species, and consequently did not represent different species. For this reason, many yeast names in common usage several decades ago are no longer accepted.