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''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...
(single-celled
fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from t ...
microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have been originally isolated from the skin of
grape A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus '' Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters. The cultivation of grapes began perhaps 8,000 years a ...
s. It is one of the most intensively studied
eukaryotic Eukaryotes () are organisms whose Cell (biology), cells have a cell nucleus, nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the ...
model organisms in molecular and cell biology, much like ''
Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...
'' as the model
bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...
. It is the microorganism behind the most common type of fermentation. ''S. cerevisiae'' cells are round to ovoid, 5–10  μm in diameter. It reproduces by
budding Budding or blastogenesis is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. For example, the small bulb-like projection coming out from the yeast cell is kno ...
. Many proteins important in human biology were first discovered by studying their
homologs A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization. Homologs have the same genes in the same loci where they provide points alon ...
in yeast; these proteins include
cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA (DNA replication) and some of its organelles, and sub ...
proteins,
signaling protein In biology, cell signaling (cell signalling in British English) or cell communication is the ability of a cell to receive, process, and transmit signals with its environment and with itself. Cell signaling is a fundamental property of all cellul ...
s, and protein-processing
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
s. ''S. cerevisiae'' is currently the only yeast cell known to have Berkeley bodies present, which are involved in particular secretory pathways. Antibodies against ''S. cerevisiae'' are found in 60–70% of patients with Crohn's disease and 10–15% of patients with
ulcerative colitis Ulcerative colitis (UC) is a long-term condition that results in inflammation and ulcers of the colon and rectum. The primary symptoms of active disease are abdominal pain and diarrhea mixed with blood (hematochezia). Weight loss, fever, and ...
, and may be useful as part of a panel of serological markers in differentiating between inflammatory bowel diseases (e.g. between ulcerative colitis and Crohn's disease), their localisation and severity.


Etymology

"''Saccharomyces''" derives from Latinized
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
and means "sugar-mould" or "sugar-fungus", ''saccharon'' (σάκχαρον) being the combining form "sugar" and ''myces'' (μύκης) being "
fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from t ...
". ''cerevisiae'' comes from Latin and means "of beer". Other names for the organism are: * Brewer's yeast, though other species are also used in brewing * Ale yeast * Top-fermenting yeast *
Baker's yeast Baker's yeast is the common name for the strains of yeast commonly used in baking bread and other bakery products, serving as a leavening agent which causes the bread to rise (expand and become lighter and softer) by converting the fermentabl ...
* Ragi yeast, in connection to making tapai * Budding yeast This species is also the main source of
nutritional yeast Nutritional yeast (also known as nooch) is a deactivated yeast, often a strain of ''Saccharomyces cerevisiae'', that is sold commercially as a food product. It is sold in the form of yellow flakes, granules, or powder and can be found in the bul ...
and
yeast extract Yeast extracts consist of the cell contents of yeast without the cell walls; they are used as food additives or flavorings, or as nutrients for bacterial culture media. They are often used to create savory flavors and umami taste sensations, ...
.


History

In the 19th century, bread bakers obtained their yeast from beer brewers, and this led to sweet-fermented breads such as the Imperial " Kaisersemmel" roll, which in general lacked the sourness created by the acidification typical of ''
Lactobacillus ''Lactobacillus'' is a genus of Gram-positive, aerotolerant anaerobes or microaerophilic, rod-shaped, non-spore-forming bacteria. Until 2020, the genus ''Lactobacillus'' comprised over 260 phylogenetically, ecologically, and metabolically div ...
''. However, beer brewers slowly switched from top-fermenting (''S. cerevisiae'') to bottom-fermenting ('' S. pastorianus'') yeast. The Vienna Process was developed in 1846. While the innovation is often popularly credited for using steam in baking ovens, leading to a different crust characteristic, it is notable for including procedures for high milling of grains (see Vienna grits ), cracking them incrementally instead of mashing them with one pass; as well as better processes for growing and harvesting top-fermenting yeasts, known as press-yeast. Refinements in microbiology following the work of Louis Pasteur led to more advanced methods of culturing pure strains. In 1879, Great Britain introduced specialized growing vats for the production of ''S. cerevisiae'', and in the United States around the turn of the century centrifuges were used for concentrating the yeast, turning yeast production into a major industrial process which simplified its distribution, reduced unit costs and contributed to the commercialisation and commoditisation of bread and beer. Fresh "cake yeast" became the standard leaven for bread bakers in much of the Western world during the early 20th century. During
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...
, Fleischmann's developed a granulated active dry yeast for the United States armed forces, which did not require refrigeration and had a longer shelf-life and better temperature tolerance than fresh yeast; it is still the standard yeast for US military recipes. The company created yeast that would rise twice as fast, cutting down on baking time. Lesaffre would later create instant yeast in the 1970s, which has gained considerable use and market share at the expense of both fresh and dry yeast in their various applications.


Biology


Ecology

In nature, yeast cells are found primarily on ripe fruits such as grapes (before maturation, grapes are almost free of yeasts). ''S. cerevisiae'' can also be found year-round in the bark of
oak trees An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...
. Since ''S. cerevisiae'' is not airborne, it requires a vector to move. Queens of social wasps overwintering as adults (''
Vespa crabro The European hornet (''Vespa crabro'') is the largest eusocial wasp native to Europe. It is also the only true hornet (genus ''Vespa'') found in North America, having been introduced to the United States and Canada from Europe as early as 1840. ...
'' and '' Polistes'' spp.) can harbor yeast cells from autumn to spring and transmit them to their progeny. The intestine of ''
Polistes dominula The European paper wasp (''Polistes dominula'') is one of the most common and well-known species of social wasps in the genus '' Polistes''. Its diet is more diverse than those of most ''Polistes'' species—many genera of insects versus mainly c ...
'', a social wasp, hosts ''S. cerevisiae'' strains as well as ''S. cerevisiae'' × '' S. paradoxus'' hybrids. Stefanini et al. (2016) showed that the intestine of ''Polistes dominula'' favors the mating of ''S. cerevisiae'' strains, both among themselves and with ''S. paradoxus'' cells by providing environmental conditions prompting cell
sporulation In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...
and spores germination. The optimum temperature for growth of ''S. cerevisiae'' is .


Life cycle

Two forms of yeast cells can survive and grow: haploid and diploid. The haploid cells undergo a simple lifecycle of mitosis and growth, and under conditions of high stress will, in general, die. This is the asexual form of the fungus. The diploid cells (the preferential 'form' of yeast) similarly undergo a simple lifecycle of mitosis and growth. The rate at which the mitotic cell cycle progresses often differs substantially between haploid and diploid cells. Under conditions of
stress Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
, diploid cells can undergo
sporulation In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...
, entering
meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately r ...
and producing four haploid
spores In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...
, which can subsequently mate. This is the
sexual Sex is the biological distinction of an organism between male and female. Sex or SEX may also refer to: Biology and behaviour *Animal sexual behaviour **Copulation (zoology) **Human sexual activity **Non-penetrative sex, or sexual outercourse ** ...
form of the
fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from t ...
. Under optimal conditions, yeast cells can double their population every 100 minutes. However, growth rates vary enormously between strains and between environments. Mean replicative lifespan is about 26 cell divisions. In the wild, recessive deleterious mutations accumulate during long periods of asexual reproduction of diploids, and are purged during
selfing Autogamy, or self-fertilization, refers to the fusion of two gametes that come from one individual. Autogamy is predominantly observed in the form of self-pollination, a reproductive mechanism employed by many flowering plants. However, species ...
: this purging has been termed "genome renewal".


Nutritional requirements

All strains of ''S. cerevisiae'' can grow aerobically on
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
, maltose, and
trehalose Trehalose (from Turkish '' tıgala'' – a sugar derived from insect cocoons + -ose) is a sugar consisting of two molecules of glucose. It is also known as mycose or tremalose. Some bacteria, fungi, plants and invertebrate animals synthesize it ...
and fail to grow on lactose and cellobiose. However, growth on other
sugars Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...
is variable.
Galactose Galactose (, '' galacto-'' + ''-ose'', "milk sugar"), sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweet as glucose, and about 65% as sweet as sucrose. It is an aldohexose and a C-4 epimer of glucose. A galactose molecu ...
and fructose are shown to be two of the best fermenting sugars. The ability of yeasts to use different sugars can differ depending on whether they are grown aerobically or anaerobically. Some strains cannot grow anaerobically on sucrose and trehalose. All strains can use
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
and
urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...
as the sole
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
source, but cannot use nitrate, since they lack the ability to reduce them to ammonium
ions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
. They can also use most amino acids, small peptides, and nitrogen bases as nitrogen sources.
Histidine Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated –NH3+ form under biological conditions), a carboxylic acid group (which is in the d ...
,
glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid ( carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinog ...
,
cystine Cystine is the oxidized derivative of the amino acid cysteine and has the formula (SCH2CH(NH2)CO2H)2. It is a white solid that is poorly soluble in water. As a residue in proteins, cystine serves two functions: a site of redox reactions and a mec ...
, and lysine are, however, not readily used. ''S. cerevisiae'' does not excrete
proteases A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the for ...
, so extracellular protein cannot be metabolized. Yeasts also have a requirement for
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
, which is assimilated as a dihydrogen phosphate ion, and sulfur, which can be assimilated as a
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
ion or as organic sulfur compounds such as the
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s methionine and cysteine. Some metals, like
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
,
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
,
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
, and
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
, are also required for good growth of the yeast. Concerning organic requirements, most strains of ''S. cerevisiae'' require biotin. Indeed, a ''S. cerevisiae''-based growth assay laid the foundation for the isolation, crystallisation, and later structural determination of biotin. Most strains also require pantothenate for full growth. In general, ''S. cerevisiae'' is prototrophic for vitamins.


Mating

Yeast has two mating types, a and α (''alpha''), which show primitive aspects of sex differentiation. As in many other eukaryotes, mating leads to genetic recombination, i.e. production of novel combinations of chromosomes. Two haploid yeast cells of opposite mating type can mate to form diploid cells that can either sporulate to form another generation of haploid cells or continue to exist as diploid cells. Mating has been exploited by biologists as a tool to combine genes, plasmids, or proteins at will. The mating pathway employs a
G protein-coupled receptor G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of evolutionarily-related p ...
,
G protein G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior. Their a ...
, RGS protein, and three-tiered
MAPK A mitogen-activated protein kinase (MAPK or MAP kinase) is a type of protein kinase that is specific to the amino acids serine and threonine (i.e., a serine/threonine-specific protein kinase). MAPKs are involved in directing cellular responses to ...
signaling cascade that is homologous to those found in humans. This feature has been exploited by biologists to investigate basic mechanisms of signal transduction and desensitization.


Cell cycle

Growth in yeast is synchronised with the growth of the
bud In botany, a bud is an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of a stem. Once formed, a bud may remain for some time in a dormant condition, or it may form a shoot immediately. Buds may be spec ...
, which reaches the size of the mature cell by the time it separates from the parent cell. In well nourished, rapidly growing yeast
cultures Culture () is an umbrella term which encompasses the social behavior, institutions, and norms found in human societies, as well as the knowledge, beliefs, arts, laws, customs, capabilities, and habits of the individuals in these groups.Tylo ...
, all the cells have buds, since bud formation occupies the whole
cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA (DNA replication) and some of its organelles, and sub ...
. Both mother and daughter cells can initiate bud formation before cell separation has occurred. In yeast cultures growing more slowly, cells lacking buds can be seen, and bud formation only occupies a part of the cell cycle.


Cytokinesis

Cytokinesis enables budding yeast ''Saccharomyces cerevisiae'' to divide into two daughter cells. ''S. cerevisiae'' forms a bud which can grow throughout its cell cycle and later leaves its mother cell when mitosis has completed.Morgan, David (2007). The Cell Cycle: Principles of Control. Sinauer Associates. ''S. cerevisiae'' is relevant to cell cycle studies because it divides asymmetrically by using a polarized cell to make two daughters with different fates and sizes. Similarly, stem cells use asymmetric division for self-renewal and differentiation.


= Timing

= For many cells, M phase does not happen until S phase is complete. However, for entry into mitosis in ''S. cerevisiae'' this is not true. Cytokinesis begins with the budding process in late G1 and is not completed until about halfway through the next cycle. The assembly of the spindle can happen before S phase has finished duplicating the chromosomes. Additionally, there is a lack of clearly defined G2 in between M and S. Thus, there is a lack of extensive regulation present in higher eukaryotes. When the daughter emerges, the daughter is two-thirds the size of the mother. Throughout the process, the mother displays little to no change in size. The RAM pathway is activated in the daughter cell immediately after cytokinesis is complete. This pathway makes sure that the daughter has separated properly.


= Actomyosin ring and primary septum formation

= Two interdependent events drive cytokinesis in ''S. cerevisiae''. The first event is contractile actomyosin ring (AMR) constriction and the second event is formation of the primary septum (PS), a chitinous cell wall structure that can only be formed during cytokinesis. The PS resembles in animals the process of extracellular matrix remodeling. When the AMR constricts, the PS begins to grow. Disrupting AMR misorients the PS, suggesting that both have a dependent role. Additionally, disrupting the PS also leads to disruptions in the AMR, suggesting both the actomyosin ring and primary septum have an interdependent relationship. The AMR, which is attached to the cell membrane facing the cytosol, consists of actin and myosin II molecules that coordinate the cells to split. The ring is thought to play an important role in ingression of the plasma membrane as a contractile force. Proper coordination and correct positional assembly of the contractile ring depends on septins, which is the precursor to the septum ring. These GTPases assemble complexes with other proteins. The septins form a ring at the site where the bud will be created during late G1. They help promote the formation of the actin-myosin ring, although this mechanism is unknown. It is suggested they help provide structural support for other necessary cytokinesis processes. After a bud emerges, the septin ring forms an hourglass. The septin hourglass and the myosin ring together are the beginning of the future division site. The septin and AMR complex progress to form the primary septum consisting of glucans and other chitinous molecules sent by vesicles from the Golgi body. After AMR constriction is complete, two secondary septums are formed by glucans. How the AMR ring dissembles remains poorly unknown. Microtubules do not play as significant a role in cytokinesis compared to the AMR and septum. Disruption of microtubules did not significantly impair polarized growth. Thus, the AMR and septum formation are the major drivers of cytokinesis.


= Differences from fission yeast

= * Budding yeast form a bud from the mother cell. This bud grows during the cell cycle and detaches; fission yeast divide by forming a cell wall * Cytokinesis begins at G1 for budding yeast, while cytokinesis begins at G2 for fission yeast. Fission yeast "select" the midpoint, whereas budding yeast "select" a bud site * During early anaphase the actomyosin ring and septum continues to develop in budding yeast, in fission yeast during metaphase-anaphase the actomyosin ring begins to develop


In biological research


Model organism

When researchers look for an organism to use in their studies, they look for several traits. Among these are size, generation time, accessibility, manipulation, genetics, conservation of mechanisms, and potential economic benefit. The yeast species ''
S. pombe ''Schizosaccharomyces pombe'', also called "fission yeast", is a species of yeast used in traditional brewing and as a model organism in molecular and cell biology. It is a unicellular eukaryote, whose cells are rod-shaped. Cells typically measur ...
'' and ''S. cerevisiae'' are both well studied; these two species diverged approximately , and are significant tools in the study of DNA damage and repair mechanisms. ''S. cerevisiae'' has developed as a model organism because it scores favorably on a number of these criteria. * As a single-cell organism, ''S. cerevisiae'' is small with a short generation time (doubling time 1.25–2 hours at ) and can be easily cultured. These are all positive characteristics in that they allow for the swift production and maintenance of multiple specimen lines at low cost. * ''S. cerevisiae'' divides with meiosis, allowing it to be a candidate for sexual genetics research. * ''S. cerevisiae'' can be transformed allowing for either the addition of new genes or deletion through
homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may ...
. Furthermore, the ability to grow ''S. cerevisiae'' as a haploid simplifies the creation of gene knockout strains. * As a eukaryote, ''S. cerevisiae'' shares the complex internal cell structure of plants and animals without the high percentage of non-coding DNA that can confound research in higher eukaryotes. * ''S. cerevisiae'' research is a strong economic driver, at least initially, as a result of its established use in industry.


In the study of aging

For more than five decades ''S. cerevisiae'' has been studied as a model organism to better understand aging and has contributed to the identification of more mammalian genes affecting aging than any other model organism. Some of the topics studied using yeast are
calorie restriction Calorie restriction (caloric restriction or energy restriction) is a dietary regimen that reduces intake of energy from caloric foods & beverages without incurring malnutrition. "Reduce" can be defined relative to the subject's previous intake b ...
, as well as in genes and cellular pathways involved in senescence. The two most common methods of measuring aging in yeast are Replicative Life Span (RLS), which measures the number of times a cell divides, and Chronological Life Span (CLS), which measures how long a cell can survive in a non-dividing stasis state. Limiting the amount of glucose or amino acids in the growth medium has been shown to increase RLS and CLS in yeast as well as other organisms. At first, this was thought to increase RLS by up-regulating the sir2 enzyme, however it was later discovered that this effect is independent of
sir2 Sirtuin 1, also known as NAD-dependent deacetylase sirtuin-1, is a protein that in humans is encoded by the SIRT1 gene. SIRT1 stands for sirtuin (silent mating type information regulation 2 homolog) 1 (''S. cerevisiae''), referring to the fact t ...
. Over-expression of the genes sir2 and fob1 has been shown to increase RLS by preventing the accumulation of
extrachromosomal rDNA circle Extrachromosomal rDNA circles (aka ERC) are pieces of extrachromosomal circular DNA (eccDNA) derived from ribosomal DNA (rDNA). Initially found in baker's yeast, these self-replicating circles are suggested to contribute to their aging and found i ...
s, which are thought to be one of the causes of senescence in yeast. The effects of dietary restriction may be the result of a decreased signaling in the TOR cellular pathway. This pathway modulates the cell's response to nutrients, and mutations that decrease TOR activity were found to increase CLS and RLS. This has also been shown to be the case in other animals. A yeast mutant lacking the genes and
Ras2 Ras2 is a ''Saccharomyces cerevisiae'' guanine nucleotide-binding protein (encoded by the RAS2 gene) which becomes activated by binding GTP when glucose is present in the environment. It affects growth regulation and starvation response. Modifica ...
has recently been shown to have a tenfold increase in chronological lifespan under conditions of calorie restriction and is the largest increase achieved in any organism. Mother cells give rise to progeny buds by mitotic divisions, but undergo replicative aging over successive generations and ultimately die. However, when a mother cell undergoes
meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately r ...
and
gametogenesis Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic di ...
, lifespan is reset. The replicative potential of
gametes A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...
(
spores In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...
) formed by aged cells is the same as gametes formed by young cells, indicating that age-associated damage is removed by meiosis from aged mother cells. This observation suggests that during meiosis removal of age-associated damages leads to
rejuvenation Rejuvenation is a medical discipline focused on the practical reversal of the aging process. Rejuvenation is distinct from life extension. Life extension strategies often study the causes of aging and try to oppose those causes in order to slow ...
. However, the nature of these damages remains to be established. During starvation of non-replicating ''S. cerevisiae'' cells,
reactive oxygen species In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen. The reduction of molecular oxygen () p ...
increase leading to the accumulation of DNA damages such as apurinic/apyrimidinic sites and double-strand breaks. Also in non-replicating cells the ability to
repair The technical meaning of maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure, and supporting utilities in industrial, business, and residential installa ...
endogenous double-strand breaks declines during chronological aging.


Meiosis, recombination and DNA repair

''S. cerevisiae'' reproduces by mitosis as diploid cells when nutrients are abundant. However, when starved, these cells undergo meiosis to form haploid spores. Evidence from studies of ''S. cerevisiae'' bear on the adaptive function of meiosis and recombination.
Mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA replication, DNA or viral repl ...
s defective in genes essential for meiotic and mitotic recombination in ''S. cerevisiae'' cause increased sensitivity to radiation or DNA damaging chemicals. For instance, gene ''rad52'' is required for both meiotic recombination and mitotic recombination. ''Rad52'' mutants have increased sensitivity to killing by
X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10  picometers to 10  nanometers, corresponding to frequencies in the range 30&nb ...
s, Methyl methanesulfonate and the DNA cross-linking agent 8-methoxypsoralen-plus-UVA, and show reduced meiotic recombination. These findings suggest that recombination repair during meiosis and mitosis is needed for repair of the different damages caused by these agents. Ruderfer et al. (2006) analyzed the ancestry of natural ''S. cerevisiae'' strains and concluded that outcrossing occurs only about once every 50,000 cell divisions. Thus, it appears that in nature, mating is likely most often between closely related yeast cells. Mating occurs when haploid cells of opposite mating type MATa and MATα come into contact. Ruderfer et al. pointed out that such contacts are frequent between closely related yeast cells for two reasons. The first is that cells of opposite mating type are present together in the same ascus, the sac that contains the cells directly produced by a single meiosis, and these cells can mate with each other. The second reason is that haploid cells of one mating type, upon cell division, often produce cells of the opposite mating type with which they can mate. The relative rarity in nature of meiotic events that result from outcrossing is inconsistent with the idea that production of genetic variation is the main selective force maintaining meiosis in this organism. However, this finding is consistent with the alternative idea that the main selective force maintaining meiosis is enhanced recombinational repair of DNA damage, since this benefit is realized during each meiosis, whether or not out-crossing occurs.


Genome sequencing

''S. cerevisiae'' was the first eukaryotic
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...
to be completely sequenced. The genome sequence was released to the
public domain The public domain (PD) consists of all the creative work to which no exclusive intellectual property rights apply. Those rights may have expired, been forfeited, expressly waived, or may be inapplicable. Because those rights have expired, ...
on April 24, 1996. Since then, regular updates have been maintained at the ''Saccharomyces'' Genome Database. This
database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases s ...
is a highly annotated and cross-referenced database for yeast researchers. Another important ''S. cerevisiae'' database is maintained by the Munich Information Center for Protein Sequences (MIPS). The ''S. cerevisiae'' genome is composed of about 12,156,677 base pairs and 6,275
gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
s, compactly organized on 16 chromosomes. Only about 5,800 of these genes are believed to be functional. It is estimated at least 31% of yeast genes have
homologs A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization. Homologs have the same genes in the same loci where they provide points alon ...
in the human genome. Yeast genes are classified using gene symbols (such as Sch9) or systematic names. In the latter case the 16 chromosomes of yeast are represented by the letters A to P, then the gene is further classified by a sequence number on the left or right arm of the chromosome, and a letter showing which of the two DNA strands contains its coding sequence. Examples: * YBR134C (aka SUP45 encoding eRF1, a translation termination factor) is located on the right arm of chromosome 2 and is the 134th open reading frame (ORF) on that arm, starting from the centromere. The coding sequence is on the Crick strand of the DNA. * YDL102W (aka POL3 encoding a subunit of
DNA polymerase delta DNA polymerase delta (DNA Pol δ) is an enzyme complex found in eukaryotes that is involved in DNA replication and repair. The DNA polymerase delta complex consists of 4 subunits: POLD1, POLD2, POLD3, and POLD4. DNA Pol δ is an enzyme used fo ...
) is located on the left arm of chromosome 4; it is the 102nd ORF from the centromere and codes from the Watson strand of the DNA.


Gene function and interactions

The availability of the ''S. cerevisiae'' genome sequence and a set of deletion mutants covering 90% of the yeast genome has further enhanced the power of ''S. cerevisiae'' as a model for understanding the regulation of eukaryotic cells. A project underway to analyze the genetic interactions of all double-deletion mutants through synthetic genetic array analysis will take this research one step further. The goal is to form a functional map of the cell's processes. a model of genetic interactions is most comprehensive yet to be constructed, containing "the interaction profiles for ~75% of all genes in the Budding yeast". This model was made from 5.4 million two-gene comparisons in which a double gene knockout for each combination of the genes studied was performed. The effect of the double knockout on the fitness of the cell was compared to the expected fitness. Expected fitness is determined from the sum of the results on fitness of single-gene knockouts for each compared gene. When there is a change in fitness from what is expected, the genes are presumed to interact with each other. This was tested by comparing the results to what was previously known. For example, the genes Par32, Ecm30, and Ubp15 had similar interaction profiles to genes involved in the Gap1-sorting module cellular process. Consistent with the results, these genes, when knocked out, disrupted that process, confirming that they are part of it. From this, 170,000 gene interactions were found and genes with similar interaction patterns were grouped together. Genes with similar genetic interaction profiles tend to be part of the same pathway or biological process. This information was used to construct a global network of gene interactions organized by function. This network can be used to predict the function of uncharacterized genes based on the functions of genes they are grouped with.


Other tools in yeast research

Approaches that can be applied in many different fields of biological and medicinal science have been developed by yeast scientists. These include
yeast two-hybrid Two-hybrid screening (originally known as yeast two-hybrid system or Y2H) is a molecular biology technique used to discover protein–protein interactions (PPIs) and protein–DNA interactions by testing for physical interactions (such as bind ...
for studying protein interactions and tetrad analysis. Other resources, include a gene deletion library including ~4,700 viable haploid single gene deletion strains. A GFP fusion strain library used to study protein localisation and a TAP tag library used to purify protein from yeast cell extracts. Stanford University's
yeast deletion project The yeast deletion project, formally the ''Saccharomyces'' Genome Deletion Project, is a project to create data for a near-complete collection of gene-deletion mutants of the yeast ''Saccharomyces cerevisiae''. Each strain carries a precise deletio ...
created
knockout mutation A gene knockout (abbreviation: KO) is a genetic technique in which one of an organism's genes is made inoperative ("knocked out" of the organism). However, KO can also refer to the gene that is knocked out or the organism that carries the gene k ...
s of every gene in the ''S. cerevisiae'' genome to determine their function.


Synthetic yeast chromosomes and genomes

The yeast genome is highly accessible to manipulation, hence it is an excellent model for genome engineering. The international Synthetic Yeast Genome Project (Sc2.0 or ''Saccharomyces cerevisiae version 2.0'') aims to build an entirely designer, customizable, synthetic ''S. cerevisiae'' genome from scratch that is more stable than the wild type. In the synthetic genome all
transposon A transposable element (TE, transposon, or jumping gene) is a nucleic acid sequence in DNA that can change its position within a genome, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size. Tra ...
s, repetitive elements and many introns are removed, all UAG
stop codon In molecular biology (specifically protein biosynthesis), a stop codon (or termination codon) is a codon (nucleotide triplet within messenger RNA) that signals the termination of the translation process of the current protein. Most codons in mess ...
s are replaced with UAA, and transfer RNA genes are moved to a novel neochromosome. , 6 of the 16 chromosomes have been synthesized and tested. No significant fitness defects have been found. All 16 chromosomes can be fused into one single chromosome by successive end-to-end chromosome fusions and
centromere The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers ...
deletions. The single-chromosome and wild-type yeast cells have nearly identical transcriptomes and similar phenotypes. The giant single chromosome can support cell life, although this strain shows reduced growth across environments, competitiveness,
gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...
production and viability.


Astrobiology

Among other microorganisms, a sample of living ''S. cerevisiae'' was included in the
Living Interplanetary Flight Experiment The Living Interplanetary Flight ExperimentAsian Scientist"Phobos-Grunt Mission Carrying Yinghuo-1 Space Probe Suffers Technical Glitch" Srinivas Laxman, 9 November 2011 (LIFE or Phobos LIFE) was an interplanetary mission developed by the Planetar ...
, which would have completed a three-year interplanetary round-trip in a small capsule aboard the Russian
Fobos-Grunt Fobos-Grunt or Phobos-Grunt (russian: link=no, Фобос-Грунт, where ''грунт'' refers to the ''ground'' in the narrow geological meaning of any type of soil or rock exposed on the surface) was an attempted Russian sample return mis ...
spacecraft, launched in late 2011. The goal was to test whether selected
organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
s could survive a few years in deep space by flying them through interplanetary space. The experiment would have tested one aspect of transpermia, the hypothesis that
life Life is a quality that distinguishes matter that has biological processes, such as Cell signaling, signaling and self-sustaining processes, from that which does not, and is defined by the capacity for Cell growth, growth, reaction to Stimu ...
could survive space travel, if protected inside rocks blasted by impact off one planet to land on another. Fobos-Grunt's mission ended unsuccessfully, however, when it failed to escape low Earth orbit. The spacecraft along with its instruments fell into the Pacific Ocean in an uncontrolled re-entry on January 15, 2012. The next planned exposure mission in deep space using ''S. cerevisiae'' is
BioSentinel BioSentinel is a lowcost CubeSat spacecraft on a astrobiology mission that will use budding yeast to detect, measure, and compare the impact of deep space radiation on DNA repair over long time beyond low Earth orbit. Selected in 2013 for a ...
. (see: List of microorganisms tested in outer space)


In commercial applications


Brewing

''Saccharomyces cerevisiae'' is used in brewing beer, when it is sometimes called a
top-fermenting Brewing is the production of beer by steeping a starch source (commonly cereal grains, the most popular of which is barley) in water and fermenting the resulting sweet liquid with yeast. It may be done in a brewery by a commercial brewer, ...
or top-cropping yeast. It is so called because during the fermentation process its hydrophobic surface causes the flocs to adhere to CO2 and rise to the top of the fermentation vessel. Top-fermenting yeasts are fermented at higher temperatures than the lager yeast ''
Saccharomyces pastorianus ''Saccharomyces pastorianus'' is a yeast used industrially for the production of lager beer, and was named in honour of Louis Pasteur by the German Max Reess in 1870. This yeast's complicated genome appears to be the result of hybridisation bet ...
'', and the resulting beers have a different flavor from the same beverage fermented with a lager yeast. "Fruity esters" may be formed if the yeast undergoes temperatures near , or if the fermentation temperature of the beverage fluctuates during the process. Lager yeast normally ferments at a temperature of approximately , where ''Saccharomyces cerevisiae'' becomes dormant. A variant yeast known as ''Saccharomyces cerevisiae'' var. ''diastaticus'' is a beer spoiler which can cause secondary fermentations in packaged products. In May 2013, the
Oregon Oregon () is a state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington, while the Snake River delineates much of its eastern boundary with Idaho. T ...
legislature made ''S. cerevisiae'' the official state microbe in recognition of the impact craft beer brewing has had on the state economy and the state's identity.


Baking

''S. cerevisiae'' is used in baking; the carbon dioxide generated by the fermentation is used as a
leavening agent In cooking, a leavening agent () or raising agent, also called a leaven () or leavener, is any one of a number of substances used in doughs and batters that cause a foaming action (gas bubbles) that lightens and softens the mixture. An altern ...
in bread and other baked goods. Historically, this use was closely linked to the brewing industry's use of yeast, as bakers took or bought the
barm Barm is the foam or scum formed on the top of a fermenting liquid, such as beer, wine, or feedstock for spirits or industrial ethanol distillation. It is used to leaven bread, or set up fermentation in a new batch of liquor. Barm, as a leaven, h ...
or yeast-filled foam from brewing ale from the brewers (producing the
barm cake A barm cake is a soft, round, flattish bread roll from North West England, traditionally leavened with barm. Chips are a popular filling, sold in most fish and chip shops in the North West of England and often called a chip barm. Another popu ...
); today, brewing and baking yeast strains are somewhat different.


Nutritional yeast

''Saccharomyces cerevisiae'' is the main source of nutritional yeast, which is sold commercially as a food product. It is popular with vegans and vegetarians as an ingredient in cheese substitutes, or as a general food additive as a source of vitamins and minerals, especially amino acids and B-complex vitamins.


Uses in aquaria

Owing to the high cost of commercial CO2 cylinder systems, CO2 injection by yeast is one of the most popular
DIY "Do it yourself" ("DIY") is the method of building, modifying, or repairing things by oneself without the direct aid of professionals or certified experts. Academic research has described DIY as behaviors where "individuals use raw and sem ...
approaches followed by aquaculturists for providing CO2 to underwater aquatic plants. The yeast culture is, in general, maintained in plastic bottles, and typical systems provide one bubble every 3–7 seconds. Various approaches have been devised to allow proper absorption of the gas into the water.


Direct use in medicine

''Saccharomyces cerevisiae'' is used as a
probiotic Probiotics are live microorganisms promoted with claims that they provide health benefits when consumed, generally by improving or restoring the gut microbiota. Probiotics are considered generally safe to consume, but may cause bacteria- host ...
in humans and animals. The strain '' Saccharomyces cerevisiae var. boulardii'' is industrially manufactured and used clinically as a medication. Several clinical and experimental studies have shown that ''S. cerevisiae var. boulardii'' is, to lesser or greater extent, useful for prevention or treatment of several gastrointestinal diseases. Moderate quality evidence has shown ''S. cerevisiae var. boulardii'' reduces risk of antibiotic-associated diarrhoea both in adults and in children and to reduce risk of adverse effects of ''
Helicobacter pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, microaerophilic, spiral (helical) bacterium usually found in the stomach. Its helical shape (from which the genus name, helicobacter, derives) is thoug ...
'' eradication therapy. There is some evidence to support efficacy of ''S. cerevisiae var. boulardii'' in prevention (but not treatment) of traveler's diarrhoea and, at least as an adjunct medication, in treatment of acute diarrhoea in adults and children and of persistent diarrhoea in children. It may also reduce symptoms of allergic rhinitis. Administration of ''S. cerevisiae var. boulardii'' is considered generally safe. In clinical trials it was well tolerated by patients, and adverse effects rate was similar to that in control groups (i. e. groups with '' placebo'' or no treatment). No case of ''S. cerevisiae var. boulardii'' fungemia has been reported during clinical trials. In clinical practice, however, cases of fungemia, caused by ''S. cerevisiae var. boulardii'' are reported. Patients with compromised immunity or those with central vascular catheters are at special risk. Some researchers have recommended avoiding use of ''S. cerevisiae var. boulardii'' as treatment in such patients. Others suggest only that caution must be exercised with its use in risk group patients.


A human pathogen

''Saccharomyces cerevisiae'' is proven to be an opportunistic human pathogen, though of relatively low
virulence Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ...
. Despite widespread use of this microorganism at home and in industry, contact with it very rarely leads to infection. ''Saccharomyces cerevisiae'' was found in the skin, oral cavity, oropharinx, duodenal mucosa, digestive tract, and vagina of healthy humans (one review found it to be reported for 6% of samples from human intestine). Some specialists consider ''S. cerevisiae'' to be a part of the normal microbiota of the gastrointestinal tract, the respiratory tract, and the vagina of humans, while others believe that the species cannot be called a true
commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...
because it originates in food. Presence of ''S. cerevisiae'' in the human digestive system may be rather transient; for example, experiments show that in the case of oral administration to healthy individuals it is eliminated from the intestine within 5 days after the end of administration. Under certain circumstances, such as degraded immunity, ''Saccharomyces cerevisiae'' can cause infection in humans. Studies show that it causes 0.45–1.06% of the cases of yeast-induced vaginitis. In some cases, women suffering from ''S. cerevisiae''-induced vaginal infection were intimate partners of bakers, and the strain was found to be the same that their partners used for baking. As of 1999, no cases of ''S. cerevisiae''-induced vaginitis in women, who worked in bakeries themselves, were reported in scientific literature. Some cases were linked by researchers to the use of the yeast in home baking. Cases of infection of
oral cavity In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on t ...
and
pharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its st ...
caused by ''S. cerevisiae'' are also known.


Invasive and systemic infections

Occasionally ''Saccharomyces cerevisiae'' causes
invasive infection Invasive may refer to: *Invasive (medical) procedure *Invasive species *Invasive observation, especially in reference to surveillance *Invasively progressive spread of disease from one organ in the body to another, especially in reference to cancer ...
s (i. e. gets into the bloodstream or other normally sterile body fluid or into a deep site tissue, such as
lungs The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side ...
,
liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...
or
spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .
) that can go systemic (involve multiple organs). Such conditions are life-threatening. More than 30% cases of ''S. cerevisiae'' invasive infections lead to death even if treated. ''S. cerevisiae'' invasive infections, however, are much rarer than invasive infections caused by ''
Candida albicans ''Candida albicans'' is an opportunistic pathogenic yeast that is a common member of the human gut flora. It can also survive outside the human body. It is detected in the gastrointestinal tract and mouth in 40–60% of healthy adults. It is usu ...
'' even in patients weakened by cancer. ''S. cerevisiae'' causes 1% to 3.6% nosocomial cases of fungemia. A comprehensive review of ''S. cerevisiae'' invasive infection cases found all patients to have at least one predisposing condition. ''Saccharomyces cerevisiae'' may enter the bloodstream or get to other deep sites of the body by translocation from oral or
enteral Enteral administration is food or drug administration via the human gastrointestinal tract. This contrasts with parenteral nutrition or drug administration (Greek ''para'', "besides" + ''enteros''), which occurs from routes outside the GI tract, ...
mucosa or through contamination of intravascular catheters (e. g. central venous catheters). Intravascular catheters, antibiotic therapy and compromised immunity are major predisposing factors for ''S. cerevisiae'' invasive infection. A number of cases of fungemia were caused by intentional ingestion of living ''S. cerevisiae'' cultures for dietary or therapeutic reasons, including use of '' Saccharomyces boulardii'' (a strain of ''S. cerevisiae'' which is used as a
probiotic Probiotics are live microorganisms promoted with claims that they provide health benefits when consumed, generally by improving or restoring the gut microbiota. Probiotics are considered generally safe to consume, but may cause bacteria- host ...
for treatment of certain forms of
diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin w ...
). ''Saccharomyces boulardii'' causes about 40% cases of invasive ''Saccharomyces'' infections and is more likely (in comparison to other ''S. cerevisiae'' strains) to cause invasive infection in humans without general problems with immunity, though such adverse effect is very rare relative to ''Saccharomyces boulardii'' therapeutic administration. ''S. boulardii'' may contaminate intravascular catheters through hands of medical personnel involved in administering probiotic preparations of ''S. boulardii'' to patients. Systemic infection usually occurs in patients who have their immunity compromised due to severe illness (
HIV/AIDS Human immunodeficiency virus infection and acquired immunodeficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV), a retrovirus. Following initial infection an individual ...
,
leukemia Leukemia ( also spelled leukaemia and pronounced ) is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or ...
, other forms of
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
) or certain medical procedures (
bone marrow transplantation Hematopoietic stem-cell transplantation (HSCT) is the transplantation of multipotent hematopoietic stem cells, usually derived from bone marrow, peripheral blood, or umbilical cord blood in order to replicate inside of a patient and to produce ...
, abdominal surgery). A case was reported when a nodule was surgically excised from a lung of a man employed in baking business, and examination of the tissue revealed presence of ''Saccharomyces cerevisiae''. Inhalation of dry baking yeast powder is supposed to be the source of infection in this case.


Virulence of different strains

Not all strains of ''Saccharomyces cerevisiae'' are equally virulent towards humans. Most environmental strains are not capable of growing at temperatures above 35 °C (i. e. at temperatures of living body of humans and other mammalian). Virulent strains, however, are capable of growing at least above 37 °C and often up to 39 °C (rarely up to 42 °C). Some industrial strains are also capable of growing above 37 °C.
European Food Safety Authority The European Food Safety Authority (EFSA) is the agency of the European Union (EU) that provides independent scientific advice and communicates on existing and emerging risks associated with the food chain. EFSA was established in February 2002, ...
(as of 2017) requires that all ''S. cerevisiae'' strains capable of growth above 37 °C that are added to the food or feed chain in viable form must, as to be qualified presumably safe, show no resistance to antimycotic drugs used for treatment of yeast infections. The ability to grow at elevated temperatures is an important factor for strain's virulence but not the sole one. Other traits that are usually believed to be associated with virulence are: ability to produce certain enzymes such as
proteinase A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalysis, catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurri ...
and
phospholipase A phospholipase is an enzyme that hydrolyzes phospholipids into fatty acids and other lipophilic substances. Acids trigger the release of bound calcium from cellular stores and the consequent increase in free cytosolic Ca2+, an essential step in ...
, invasive growth (i.e. growth with intrusion into the nutrient medium), ability to adhere to mammalian cells, ability to survive in the presence of
hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...
(that is used by macrophages to kill foreign microorganisms in the body) and other abilities allowing the yeast to resist or influence immune response of the host body. Ability to form branching chains of cells, known as pseudohyphae is also sometimes said to be associated with virulence, though some research suggests that this trait may be common to both virulent and non-virulent strains of ''Saccharomyces cerevisiae''.


See also

* ''Saccharomyces cerevisiae'' extracts:
Vegemite Vegemite ( ) is a thick, dark brown Australian food spread made from leftover brewers' yeast extract with various vegetable and spice additives. It was developed by Cyril Callister in Melbourne, Victoria, in 1922. A spread for sandwiches, ...
,
Marmite Marmite ( ) is a British savoury food spread based on yeast extract, invented by the German scientist Justus von Liebig. It is made from by-products of beer brewing ( lees) and is produced by the British company Unilever. Marmite is a vegan ...
,
Cenovis Cenovis is a dark brown food paste from Switzerland consisting of yeast extract. It is similar to English Marmite, Brazilian Cenovit, and Australian Vegemite. It is rich in vitamin B1. It is used to flavour soups, sausages, and salads. The mos ...
, Guinness Yeast Extract, mannan oligosaccharides,
pgg-glucan Poly- -6-D-glucopyranosyl- -3-D-glucopyranose glucan (PGG glucan, proprietary name Betafectin) is an anti-infective agent and a form or type of beta-glucan. Betafectin is a PGG-glucan, a novel β-(1,6) branched β-(1,3) glucan, purified from the ...
,
zymosan Zymosan is a glucan with repeating glucose units connected by β-1,3-glycosidic linkages. It binds to TLR 2 Toll-like receptor 2 also known as TLR2 is a protein that in humans is encoded by the ''TLR2'' gene. TLR2 has also been designated as CD ...
* ''Saccharomyces cerevisiae boulardii'' ('' Saccharomyces boulardii'') * Flora of Door County, Wisconsin § Hybrid yeast * ''Saccharomyces cerevisiae'' genes * Auto-brewery syndrome * Biosprint * BolA-like protein family * Yeast promoter atlas (2010)


References

Footnotes Citations


Further reading

* *


External links


''Saccharomyces'' Genome Database

Yeast Resource Center Public Data Repository

Munich Information Center for Protein Sequences
*
UniProt UniProt is a freely accessible database of protein sequence and functional information, many entries being derived from genome sequencing projects. It contains a large amount of information about the biological function of proteins derived from ...

''Saccharomyces cerevisiae''
* {{Authority control Fungal models Digestive system Probiotics Osmophiles Baking Yeasts used in brewing Leavening agents Oenology Fungi described in 1883 Edible fungi