SACCHAROMYCOTINA is a subdivision (subphylum) of the division
Ascomycota in the Kingdom
Fungi . It compromises most of
the ascomycete yeasts . The members of
Saccharomycotina reproduce by
budding and they do not produce ascocarps (fruiting bodies).
The subdivision includes a single class:
Saccharomycetes , which
again contains a single order:
Notable members of
Saccharomycotina are the baker’s yeast
Saccharomyces cerevisiae and the genus Candida that includes several
* 1 Etymology
* 2 History and economic importance
* 3 Morphology
* 4 Reproduction
* 5 Distribution and ecology
* 6 Taxonomy
* 7 See also
* 8 References
* 9 External links
The name comes from the Greek word σάκχαρον (sákkharon),
meaning "sugar" and μύκης (mukēs) meaning "fungus".
HISTORY AND ECONOMIC IMPORTANCE
Historical records from ancient Egypt and China describe the process
of brewing and baking from 10 000 to 8000 years ago, and the
production of fermented beverages and foods seems to have paralleled
the beginning of agriculture . In the 1850s, Louis Pasteur
demonstrated that yeasts are responsible for the fermentation of grape
juice to wine.
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 .
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 .
Some species (e.g.
Metschnikowia species) tend to form chains of
budding cells that are termed psedohyphae . Yet other species are
able to produce true septate hyphae . Such species (e.g. Candida
albicans ) are termed dimorphic, which means they can propagate both
as budding yeasts and as filamentous hyphae.
Asexual reproduction occurs mainly vegetatively by mitosis and
Saccharomycotina is characterized by holoblastic budding,
which means all layers of the parent cell wall are involved in the
budding event. This leaves a scar through which no further budding
Asexual cells may vary in shape. The shape of the cell may be
informative in terms of detecting mode of reproduction or taxonomic
placement to genera or species.
Although not commonly known, some species form endospores
(e.g.Candida species). These are asexual spores that are formed
within their mother cell (hyphal or single cell). Strains of Candida
Metschnikowia may also form asexual resting spores called
Sexual reproduction is not known for all species of Saccharomycotina,
but may happen in certain species if environmental conditions favour
it (e.g. deficiency in nitrogen and carbohydrate ). Sexual
reproduction is well known in
Saccharomyces cerevisiae . Here, the
life cycle involves alternation between a haploid and a diploid phase.
The life cycle proceeds as follows: Two cells of different mating type
fuse and the nuclei undergo karyogamy . This results in a daughter
cell with a diploid nucleus, functioning as an ascus , where meiosis
occurs to produce haploid ascospores . When ascospores germinate, the
haploid phase is established, and is maintained by further mitosis and
budding . In most natural populations this phase is fairly short since
ascospores fuse almost immediately after meiosis has occurred. This
results in most yeast populations being diploid for most part of their
Saccharomycotina there are to mating types present. The mating
types specify peptide hormones called pheromones and corresponding
receptors for each type. These pheromones organize the mating. The
pheromones do not affect the same mating type or diploids , but bind
to receptors of different mating type. Interaction between pheromone
and receptor results in altered metabolism to allow for fusion between
cells of different mating type.
DISTRIBUTION AND ECOLOGY
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. 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).
Examples of ecological modes in Saccharomycotina:
* Associations with insects
* Associations with plants, including
Saccharomyces cerevisiae with
* Plant parasitism (e.g. cotton boll rot by Eremothecium ashbyi,
Eremothecium gossypii as pathogen on coffee, soybean and other crops)
* Saprotrophism on leaves and decaying wood (e.g. Ogataea)
* Human pathogens (e.g. species of Candida and Meyerozyma)
Although yeasts are commonly isolated from soil, few are believed to
have soil as a primary habitat .
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
Ascomycota . It is a sister group to
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.
considered to be a polyphyletic group, consisting of members of
Taphrinomycotina , as well ass Saccharomycotina. This
realization has led to major changes in the phylogeny and taxonomy of
In addition, the recent changes in the International Code of
Nomenclature for algae, fungi and plants 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.
The genus Candida is an example of a genus that is undergoing
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
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