the saccharomyces cerevisiae world
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The Saccharomyces cerevisiae World - Diversity
Taxonomy, Phylogeny & Classification
Figure 1. Phylogenetic tree of Saccharomyces cerevisiae. (http://bioweb.uwlax.edu/bio203/s2007/nelson_andr/)
Although there are over 1,500 species of yeasts, the term, yeast, often refers to S. cerevisiae. Astonishingly, This organism has 16 linear chromosomes and 5,770 genes. “Saccharomyces” is derived from Latinized Greek and has the meaning of “sugar mold” or “sugar fungus,” where Saccharo- is the combining form of “sugar-” and myces being “fungus.” Cerevisiaeis derived from Latin and has the meaning “of beer.” Altogether, Saccharomyces cerevisiae means sugar fungus of the beer. Other common names of S. cerevisiae are:
S. cerevisiae (short form of the scientific name) Brewer’s yeast Ale yeast Top-fermenting yeast Baker’s yeast Budding yeast
S. cerevisiae is in the Fungi Kingdom. The reasons for this classification are:1. It has a cell wall that is made of chitin, which is a polymer of nitrogen
containing polysaccharide [(C8H13O5N)n] forming a tough, protective covering or structural support in certain organisms,
2. It has no peptidoglycan (a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria, forming the cell wall) in its cell walls,
3. And its lipids are ester (a chemical compound consisting of a carbonyl adjacent to an ether linkage) linked.
S. cerevisiae also performs protein synthesis through the usage of a DNA template and it consists of relatively larger ribosomes. Finally, S. cerevisiae is considered a yeast as it is a unicellular organism that cannot form a fruiting body. S. cerevisiae could be then differentiated from other yeast species based on their growth characteristics and physiological traits: their ability to ferment individual sugars.
In fact, the initial classification of S. cerevisiae was based on morphological characteristics with specific physiological and biochemical traits that are used to differentiate between other species with similar morphological traits. However, due to the development of genetic technologies, the species, S. cerevisiae, may be divided into four separate species based on DNA homology studies in the future. The four possible species are: S. cerevisiae, S. bayanus (S. uvarum), S. pasteurianus (S. carlsbergensis), and S. paradoxus.
Very Brief Description of each taxonomic level of Saccharomyces cerevisiae
Figure 2. Taxonomy of S. cerevisiae from its domain level to species level. Created by Daniel Seo.
Domain-Eukarya: possesses a nucleus containing the organism's genetic information, a cell membrane, and membrane-bound organelles.Kindgom-Fungi: possesses cell walls that are made of chitin, fruiting body, alternation or generations, and fungal organisms are heterotrophic.Phylum-Ascomycota: able to reproduce both asexually and sexually, internal spores called ascus, single celled or multi-cellular, Class-Saccharomycetes: single celled fungi called yeast, do not possess a fruiting body, and feed on sugarOrder-Saccharomycetales: feed on primarily plant sugars, and comprises of budding yeasts.Family-Saccharomycetaceae: reproduces by budding and ferment carbohydratesGenus-Saccharomyces: sparse or absent mycelium, and reproduces asexually by budding Species-S. cerevisiae: Saccharomyces cerevisiae are commonly used in labs and in food products such as breads and beers.Phylogeny of S. cerevisiae
Note: this study was performed by Robert Montrocher, Marie-Christine Verner, Jerome Biolay,
Christian Gautier, and Roland Marmeisse.
The phylogenetic relationships between species of yeast that belongs to the Saccharomyces sensu strict group, which includes Saccharomyces cerevisiae and Saccharomyces bayanus, were studied. The gene trees generated in this study displayed the distribution of the yeast species into two major, distinct, phylogenetic groups called ‘cerevisiae’ and ‘bayanus.’ In the ‘cerevisiae’ group, strains of S. cerevisiae were found with 16 other species from the total of 23. On the other hand, the ‘bayanus’ group was composed of the remaining seven species. This result suggested that S. cerevisiae andS. paradoxus are two distinct taxa.
List of Saccharomyces sensu strict type strains studied:
Figure 3. The strains of species listed above were studied to perform a phylogenetic analysis on S. cerevisiae and otherSaccharomyces species. (Retrieved from http://ijs.sgmjournals.org/content/48/1/295.long)
In a broader view?
Figure 4. This phylogenetic tree supports the fact that fungi are more closely related to animals than other plants. (Retrieved from http://bioweb.uwlax.edu/bio203/s2009/christia_eri2/classification.htm)
This phylogenic tree shown above is very broad, but suggests a very important and interesting point. Modern molecular techniques and technologies have allowed humans to determine that fungi are more closely related to animals, as they both belong to the Unikonta supergroup, than to land plants. Many evidences such as the fact that fungal organisms are heterotrophic and store sugar in the form of glycogen, like animals do, and have cell walls that are made of chitin, unlike cellulose in land plants, support this finding.
Life Cycle and Reproduction
Figure 5. Basic structures of S. cerevisiae cells during cell cycle. (Herskowitz)
The rate of growth of S. cerevisiae cells is
synchronized with the growth rate of the bud,
which separates from its parent cell when it
reaches the size of the mature cell. In rapidly
proliferating S. cerevisiae populations,
every cell can be seen with buds on the
surface of the cell. This bud formation occupies
the entire cell cycle. In slowly growing
populations, cells lacking buds can be
found easily, and bud formation only
occupies a part of its entire cell cycle. This
cell cycle normally consists of the
following stages: G1, S, G2, and M.
Figure 6. An image of soft X-ray tomography of rapidly frozen Saccharomyces cerevisiae cells at each phase of cell cycle – G1, S, M, and G2. The organelles of the cells are colour-coded as follows: blue, nucleus; orange, nucleolus;
gray, mitochondria; ivory, vacuoles; green, lipid bodies. Scale bar, 2 μm. (Larabell & Nugent, 2010)
Figure 7. Budding S. cerevisiae cells. Scale bar, 10 μm. ("Image of budding")
Like many other fungal organisms, S. cerevisiae cells can reproduce both asexually and sexually. In fact, environmental conditions often determine the method of reproduction of these cells. Asexual reproduction of S. cerevisiae cells is called budding, while sexual reproduction of the cells is called sporulation. S. cerevisiae exists as either a diploid or a haploid cell. Both haploid and diploid S. cerevisiae cells can reproduce by mitosis under favourable environmental conditions, where daughter cells bud off from their mother cells. During the budding process, the nucleus of the parent
cell splits and locate itself towards the daughter cell. The bud continually grows and when it is fully matured, it can separate from the parent cell and function as an independent cell. Interestingly, diploid cells can undergo meiosis to produce four haploid spores that is composed of two a spores and two α spores upon facing stressful conditions, such as nutrient depletion. Haploid cells are capable of mating with other haploid cells, but of the opposite mating type (an a cell can only mate with an α cell, and vice versa) to produce a diploid cell. This process begins with the fusion of the cytoplasm, and then the haploid cells become fertilized and become a diploid zygote. After this, the zygote can undergo meiosis and form an ascus which will split into four ascospores. Finally, these haploids can then undergo germination and become haploid cells again. With sufficient and appropriate nutrition, S. cerevisiae cells can reproduce every 100 minutes. Their average replicative lifespan lasts about 26 cell divisions.
Figure 8. Life cycle of S. cerevisiae. ("Yeast Life Cycle")
Figure 9. A large population of S. cerevisiae cellscan be easily found in fermenting fruits, such as
riped grapes. (Source: http://katherinetallmadge.com/wp-content/
Saccharomyces cerevisiae is widespread and commonly found in nature. Yeast cells of this species can be found in fermenting fruits, such as grapes (although before maturation, grapes are
almost free of yeasts, inside animals), in the bark of certain deciduous trees such as Sampaio and Goncalves, and in many other high sugar environments such as nectar and sap fluxes. However, S. cerevisiae can be isolated from fruits and grains and other materials with a high concentration of carbohydrates. As a matter of fact, S. cerevisiae has a very high tolerance to alcohol and ferment glucose in the environment to alcohol. S. cerevisiae also occupies damp or wet habitats that are high in organic material. S. cerevisiae shares its habitat with numerous other organisms including various fungi species, fungal yeasts, and bacteria. The ability of S. cerevisiae to decompose a large variety of sugars and amino acids enhances
the organism's ability for long-term survival. In fact, S. cerevisiae acts as a catalyst in the process of decomposition, speeding decomposition's chemical reactions.
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Daniel Seo 님이 11th April 2013 에 게시