ABSTRACT
Yeasts comprise a group of ~700 ascomycetous or basidiomycetous fungi, whose predominant mode of vegetative reproduction is growth as single cells [1]. In other words, growth as unicellular organism is the main criterion that unifies taxonomically diverse fungi as yeasts. In addition, many molds that predominantly grow as hyphal filaments can adopt the yeast form as part of their life cycle. One of the prominent genera among yeasts is Saccharomyces, which has been used in making bread and brewing liquor throughout human history. The literary meaning of the terms used for yeasts in different languages can often be associated with the property of fermentation [2]. The English word yeast is related to the Dutch word gist or the German word Gischt which both mean foam. The French expression levure is derived from lever (=to rise) and the Latin term levere, both of which refer to the evolution of CO2 that pushes up solid substances during fermentation. Apart from Saccharomyces, many other yeast genera are of central importance in today’s biotechnology and medicine. Among others, strains of Schwanniomyces occidentalis, Kluyveromyces lactis, Pichia pastoris, Hansenula polymorpha, Yarrowia lipolytica, and Candida maltosa belong to the so-called nonconventional yeasts that are used in a wide variety of biotechnological processes of great economical importance [3].
