Saccharomycotina

The name comes from the Greek word σάκχαρον (sákkharon), meaning "sugar" and μύκης (mukēs) meaning "fungus".

Historical records from ancient Egypt and China describe the processes of brewing and baking from 10,000 to 8,000 years ago, and the production of fermented beverages and foods seems to have paralleled the beginning of agriculture.[5] In the 1850s, Louis Pasteur demonstrated that yeasts are responsible for the fermentation of grape juice to wine.[6][7]

Saccharomycotina include some of the economically most important fungi known. Members include species of industrial and agricultural importance (e.g. brewing, baking, fermentation of food products, production of citric acid, production of recombinant proteins, biofuel production, biological pest control of crops). Other species cause economic losses worldwide (plant pathogens, contaminants of foods and beverages). Yet others are animal and human pathogens.[8][9]

Saccharomycete yeasts usually grow as single cells. Their cellular morphology is fairly simple, although their growth form is highly adapted. Asci are naked and ascospores can have several forms. No species produce ascocarps (fruiting bodies). Saccharomycete genomes are often smaller than those of filamentous fungi.[2][10][11][4]

Some species (e.g. Metschnikowia species) tend to form chains of budding cells that are termed pseudohyphae.[2] Yet other species are able to produce true septate hyphae.[4] Such species (e.g. Candida albicans) are termed dimorphic, which means they can propagate both as budding yeasts and as filamentous hyphae.

Saccharomycete yeasts are found in nearly all regions of the world, including hot deserts, polar areas, in freshwater, in salt water, and in the atmosphere.[2] Their growth is mainly saprotrophic, but some members are important pathogens of plants and animals, including humans. They are often found in specialized habitats, e.g. small volumes of organic carbon rich liquid (e.g. flower nectar).[4]

Examples of ecological modes in Saccharomycotina:

• • Associations with insects[14]
  • Associations with plants, including Saccharomyces cerevisiae with grapes[15]
  • Plant parasitism (e.g. cotton boll rot by Eremothecium ashbyi, Eremothecium gossypii as pathogen on coffee, soybean and other crops)[2]
  • Saprotrophism on leaves and decaying wood (e.g. Ogataea)[16]
  • Human pathogens (e.g. species of Candida and Meyerozyma)[8][9]

Although yeasts are commonly isolated from soil, few are believed to have soil as a primary habitat.[2]

Accurate identification of species is important for understanding yeast ecology, something that is now possible with the increased use of DNA-based methods. Before molecular methods were available, identification was mainly based on morphology, something that resulted in misclassifications and further prevented reliable results of ecological research.

Saccharomycotina is a subdivision (subphylum) of the division (phylum) Ascomycota. It is a sister group to Pezizomycotina.[2][3]

Yeasts were traditionally classified as a separate group of the fungal kingdom, but in recent years DNA-based methods have changed the understanding of phylogenetic relationships among fungi. Yeasts are considered to be a polyphyletic group,[2][11] consisting of members of Basidiomycota, Taphrinomycotina, as well as Saccharomycotina. This realization has led to major changes in the phylogeny and taxonomy of Saccharomycotina.[2]

In addition, the recent changes in the International Code of Nomenclature for algae, fungi and plants[17][18] have had a major impact on the classification of fungi, including Saccharomycotina. The changes imply that a fungus can only bear one correct name, i.e. separate names for anamorphs and teleomorphs are no longer allowed. This involves major changes in Saccharomycotina taxonomy, as many species are currently described from both anamorphic and teleomorphic stages.[18] The genus Candida is an example of a genus that is undergoing large-scale revisions.

Molecular identification methods are important tools for discovery of new species and subsequently give better understanding of biodiversity in this group. Much of the future classification of Saccharomycotina will rest on phylogenetic analysis of DNA sequences rather than on the morphological and developmental characters.

• Yeast in winemaking
• Saccharomyces Genome Database

• Tree of Life: Saccharomycetales