''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 constitut ...

(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 th ...

microorganisms). The species has been instrumental in

winemaking Winemaking or vinification is the production of wine, starting with the selection of the fruit, its fermentation into alcohol, and the bottling of the finished liquid. The history of wine-making stretches over millennia. The science of wine and ...

baking Baking is a method of preparing food that uses dry heat, typically in an oven, but can also be done in hot ashes, or on hot stones. The most common baked item is bread but many other types of foods can be baked. Heat is gradually transferred " ...

, and

brewing 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, fermenting the resulting sweet liquid with Yeast#Beer, yeast. It may be done in a brewery ...

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 ago, ...

s. It is one of the most intensively studied

eukaryotic Eukaryotes () are organisms whose cells have a 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 three domains of life. Bacte ...

model organism A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workin ...

s in

molecular A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...

and

cell biology Cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function, and behavior of cells. All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living and ...

, 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 ''Escher ...

'' 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 among ...

. It is the microorganism behind the most common type of

fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...

. ''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 know ...

. Many

proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

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 locus (genetics), loci where they pr ...

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 subs ...

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 cellula ...

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. A ...

s. ''S. cerevisiae'' is currently the only yeast cell known to have Berkeley bodies present, which are involved in particular secretory pathways.

Antibodies An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...

against ''S. cerevisiae'' are found in 60–70% of patients with

Crohn's disease Crohn's disease is a type of inflammatory bowel disease (IBD) that may affect any segment of the gastrointestinal tract. Symptoms often include abdominal pain, diarrhea (which may be bloody if inflammation is severe), fever, abdominal distension ...

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 a ...

, 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 "

". ''cerevisiae'' comes from Latin and means "of beer". Other names for the organism are: *

Brewer's 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 constitu ...

, 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 fermentable ...

* Ragi yeast, in connection to making

tapai ''Tapai'' (also ''tapay'' or ''tape'') is a traditional fermented preparation of rice or other starchy foods, and is found throughout much of Southeast Asia, especially in Austronesian cultures, and parts of East Asia. It refers to both the ...

* 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, a ...

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 The Kaiser roll (''Emperor roll'', german: Kaisersemmel), also called a Vienna roll (; as made by hand also: , sl, kajzerica), or a hard roll, is a typically crusty round bread roll, originally from Austria. It is made from white flour, yeas ...

" 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 diver ...

''. 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 Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist and microbiologist renowned for his discoveries of the principles of vaccination, microbial fermentation and pasteurization, the latter of which was named afte ...

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 opposin ...

, Fleischmann's developed a

granulated Granulation is the process of forming grains or granules from a powdery or solid substance, producing a granular material. It is applied in several technological processes in the chemical and pharmaceutical industries. Typically, granulation invo ...

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 Lesaffre is a French yeast manufacturer, and the world's largest producer. History The company was founded by Louis Lesaffre, the co-founder of Bonduelle, in the mid-19th century. One of its subsidiaries, Bio Springer, was founded by Baron Max ...

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

Laboratoorne pagaripärm (Saccharomyces cerevisiae) agariplaadil

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 Wasps of the cosmopolitan genus ''Polistes'' (the only genus in the tribe Polistini) are the most familiar of the polistine wasps, and are the most common type of paper wasp in North America. Walter Ebeling coined the vernacular name "umbrella ...

'' 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 ca ...

'', 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, f ...

and spores germination. The optimum temperature for growth of ''S. cerevisiae'' is .

Life cycle

Two forms of yeast cells can survive and grow:

haploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...

and

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...

. The haploid cells undergo a simple

lifecycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia * Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring *Life-cycle hypothesis ...

mitosis In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...

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 Growth may refer to: Biology * Auxology, the study of all aspects of human physical growth * Bacterial growth * Cell growth * Growth hormone, a peptide hormone that stimulates growth * Human development (biology) * Plant growth * Secondary 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

, 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 resu ...

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, f ...

, 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

. 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 Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...

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 o ...

: 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, using ...

maltose } Maltose ( or ), also known as maltobiose or malt sugar, is a disaccharide formed from two units of glucose joined with an α(1→4) bond. In the isomer isomaltose, the two glucose molecules are joined with an α(1→6) bond. Maltose is the two- ...

, 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 Lactose is a disaccharide sugar synthesized by galactose and glucose subunits and has the molecular formula C12H22O11. Lactose makes up around 2–8% of milk (by mass). The name comes from ' (gen. '), the Latin word for milk, plus the suffix '' - ...

and

cellobiose Cellobiose is a disaccharide with the formula (C6H7(OH)4O)2O. It is classified as a reducing sugar. In terms of its chemical structure, it is derived from the condensation of a pair of β-glucose molecules forming a β(1→4) bond. It can be hyd ...

. 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 s ...

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 molec ...

and

fructose Fructose, or fruit sugar, is a Ketose, ketonic monosaccharide, simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galacto ...

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 Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refined ...

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 was ...

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 r ...

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 Nitrate is a polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...

, since they lack the ability to reduce them to

ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...

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 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 am ...

, small

peptides Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A p ...

, 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 de ...

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 proteinogeni ...

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 me ...

, and

lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. It contains an α-amino group (which is in the protonated form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −C ...

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 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 constitut ...

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 Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

, 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 ar ...

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 am ...

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 Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

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 to ...

, 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 Biotin (or vitamin B7) is one of the B vitamins. It is involved in a wide range of metabolic processes, both in humans and in other organisms, primarily related to the utilization of fats, carbohydrates, and amino acids. The name ''biotin'', bor ...

. 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 Pantothenic acid, also called vitamin B5 is a water-soluble B vitamin and therefore an essential nutrient. All animals require pantothenic acid in order to synthesize coenzyme A (CoA) – essential for fatty acid metabolism – as well as to, i ...

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 Genetic recombination (also known as genetic reshuffling) is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukaryo ...

, i.e. production of novel combinations of chromosomes. Two

yeast cells of opposite mating type can mate to form

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 act ...

RGS protein Regulators of G protein signaling (RGS) are protein structural domains or the proteins that contain these domains, that function to activate the GTPase activity of heterotrimeric G-protein G alpha subunit, α-subunits. RGS proteins are multi-func ...

, 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 Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellula ...

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.Tyl ...

, all the cells have buds, since bud formation occupies the whole

. 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 Cytokinesis () is the part of the cell division process during which the cytoplasm of a single eukaryotic cell divides into two daughter cells. Cytoplasmic division begins during or after the late stages of nuclear division in mitosis and meios ...

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 cell In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type o ...

s 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 In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatri ...

(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 meas ...

'' and ''S. cerevisiae'' are both well studied; these two species diverged approximately , and are significant tools in the study of

DNA damage DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA da ...

and repair mechanisms. ''S. cerevisiae'' has developed as a

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 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.Tylor ...

. 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 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 kno ...

strains. * As a

eukaryote Eukaryotes () are organisms whose cells have a 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 three domains of life. Bacte ...

, ''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 be ...

, as well as in genes and cellular pathways involved in

senescence Senescence () or biological aging is the gradual deterioration of functional characteristics in living organisms. The word ''senescence'' can refer to either cellular senescence or to senescence of the whole organism. Organismal senescence inv ...

. 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 A growth medium or culture medium is a solid, liquid, or semi-solid designed to support the growth of a population of microorganisms or cells via the process of cell proliferation or small plants like the moss ''Physcomitrella patens''. Differen ...

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 nicotinamide adenine dinucleotide, 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 (''Sacchar ...

. 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 in ...

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 Ageing ( BE) or aging ( AE) is the process of becoming older. The term refers mainly to humans, many other animals, and fungi, whereas for example, bacteria, perennial plants and some simple animals are potentially biologically immortal. In ...

over successive generations and ultimately die. However, when a mother cell undergoes

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 d ...

, 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 t ...

(

) 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

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 or viral replication, mi ...

s defective in genes essential for meiotic and mitotic recombination in ''S. cerevisiae'' cause increased sensitivity to

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...

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 ...

Methyl methanesulfonate Methyl methanesulfonate (MMS), also known as methyl mesylate, is an alkylating agent and a carcinogen. It is also a suspected reproductive toxicant, and may also be a skin/sense organ toxicant. It is used in cancer treatment.8-methoxypsoralen-plus-UVA, and show reduced meiotic recombination. These findings suggest that

recombination repair 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 ...

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 Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity. Outcrossing can be a useful ...

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 An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera or s ...

, 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

is inconsistent with the idea that production of

genetic variation Genetic variation is the difference in DNA among individuals or the differences between populations. The multiple sources of genetic variation include mutation and genetic recombination. Mutations are the ultimate sources 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 ge ...

to be completely sequenced. The genome sequence was released to the

public domain The public domain (PD) consists of all the creative work A creative work is a manifestation of creative effort including fine artwork (sculpture, paintings, drawing, sketching, performance art), dance, writing (literature), filmmaking, ...

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 sp ...

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 pair A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...

s 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 ba ...

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

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 Eukaryotic translation termination factor 1 (eRF1), also known as TB3-1, is a protein that in humans is encoded by the ''ETF1'' gene. In eukaryotes and archaea, this is the sole class 1 release factor (eRF) which recognizes all three stop codon ...

, 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 for ...

) 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 Synthetic genetic array analysis (SGA) is a high-throughput screening, high-throughput technique for exploring synthetic lethality, synthetic lethal and synthetic sick genetic interactions (Synthetic lethality, SSL). SGA allows for the systematic co ...

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

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 bindi ...

for studying

protein interactions Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respond ...

and

tetrad analysis The tetrad is the four spores produced after meiosis of a yeast or other Ascomycota, ''Chlamydomonas'' or other alga, or a plant. After parent haploids mate, they produce diploids. Under appropriate environmental conditions, diploids sporulate and ...

. 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 genetics, 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 ...

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. Transpo ...

s, repetitive elements and many

intron An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e. a region inside a gene."The notion of the cistron .e., gene. ...

s 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 me ...

s are replaced with UAA, and

transfer RNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino ac ...

genes are moved to a novel

neochromosome A neochromosome is a chromosome that is not normally found in nature. Cancer-associated neochromosomes are found in some cancer cells. Neochromosomes have also been created using genetic engineering techniques. Cancer-associated neochromosomes ...

. , 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 a ...

deletions. The single-chromosome and wild-type yeast cells have nearly identical

transcriptome The transcriptome is the set of all RNA transcripts, including coding and non-coding, in an individual or a population of cells. The term can also sometimes be used to refer to all RNAs, or just mRNA, depending on the particular experiment. The t ...

s 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 t ...

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 Panspermia () is the hypothesis, first proposed in the 5th century BCE by the Greek philosopher Anaxagoras, that life exists throughout the Universe, distributed by space dust, meteoroids, asteroids, comets, and planetoids, as well as by spacecraf ...

, the hypothesis that

life Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from that which does not, and is defined by the capacity for growth, reaction to stimuli, metabolism, energ ...

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 The survival of some microorganisms exposed to outer space has been studied using both simulated facilities and low Earth orbit exposures. Bacteria were some of the first organisms investigated, when in 1960 a Russian satellite carried ''Escherich ...

)

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 U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

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 alterna ...

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, has ...

or yeast-filled foam from brewing

ale Ale is a Type of beer, type of beer brewed using a Warm fermentation, warm fermentation method, resulting in a sweet, full-bodied and fruity taste. Historically, the term referred to a drink brewed without hops. As with most beers, ale typicall ...

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 popular ...

); 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 semi ...

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 i ...

in humans and animals. The strain ''

Saccharomyces cerevisiae var. boulardii ''Saccharomyces boulardii'' is a tropical yeast first isolated from lychee and mangosteen fruit peel in 1923 by French scientist Henri Boulard. Although early reports claimed distinct taxonomic, metabolic, and genetic properties, ''S. 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 though ...

'' 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 A placebo ( ) is a substance or treatment which is designed to have no therapeutic value. Common placebos include inert tablets (like sugar pills), inert injections (like Saline (medicine), saline), sham surgery, and other procedures. In general ...

'' or no treatment). No case of ''S. cerevisiae var. boulardii'' fungemia has been reported during clinical trials. In clinical practice, however, cases of

fungemia Fungemia is the presence of fungi or yeasts in the blood. The most common type, also known as candidemia, candedemia, or systemic candidiasis, is caused by '' Candida'' species; candidemia is also among the most common bloodstream infections of a ...

, 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 ca ...

. 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 ...

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 struc ...

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 of th ...

liver The liver is a major Organ (anatomy), organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of proteins and biochemicals necessary for ...

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 Systemic fundamental to a predominant social, economic, or political practice. This refers to: In medicine In medicine, ''systemic'' means affecting the whole body, or at least multiple organ systems. It is in contrast with ''topical'' or ''loc ...

(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 us ...

'' even in patients weakened by cancer. ''S. cerevisiae'' causes 1% to 3.6%

nosocomial A hospital-acquired infection, also known as a nosocomial infection (from the Greek , meaning "hospital"), is an infection that is acquired in a hospital or other health care facility. To emphasize both hospital and nonhospital settings, it is ...

cases of

. 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 The word oral may refer to: Relating to the mouth * Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid **Oral administration of medicines ** Oral examination (also known as an oral exam or oral ...

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 A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It is ...

or through contamination of intravascular catheters (e. g.

central venous catheter A central venous catheter (CVC), also known as a central line(c-line), central venous line, or central venous access catheter, is a catheter placed into a large vein. It is a form of venous access. Placement of larger catheters in more central ...

s). Intravascular catheters, antibiotic therapy and compromised immunity are major predisposing factors for ''S. cerevisiae'' invasive infection. A number of cases of

were caused by intentional ingestion of living ''S. cerevisiae'' cultures for dietary or therapeutic reasons, including use of ''

Saccharomyces boulardii ''Saccharomyces boulardii'' is a tropical yeast first isolated from lychee and mangosteen fruit peel in 1923 by French scientist Henri Boulard. Although early reports claimed distinct taxonomic, metabolic, and genetic properties, ''S. boulardii' ...

'' (a strain of ''S. cerevisiae'' which is used as a

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 wi ...

). ''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 produc ...

abdominal surgery The term abdominal surgery broadly covers Surgery, surgical procedures that involve opening the abdomen (laparotomy). Surgery of each abdominal organ is dealt with separately in connection with the description of that organ (see stomach, kidney, l ...

). 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

Hustopece 20210903 170948 Saccharomyces cerevisiae

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 Mammals () are a group of vertebrate animals constituting the class (biology), class Mammalia (), characterized by the presence of mammary glands which in Female#Mammalian female, females produce milk for feeding (nursing) their young, a ...

). 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 catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the for ...

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

macrophage Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer cel ...

s 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 A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

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''.

References

Footnotes Citations

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

Etymology

History

Biology

Ecology

Life cycle

Nutritional requirements

Mating

Cell cycle

Cytokinesis

= Timing

= Actomyosin ring and primary septum formation

= Differences from fission yeast

In biological research

Model organism

In the study of aging

Meiosis, recombination and DNA repair

Genome sequencing

Gene function and interactions

Other tools in yeast research

Synthetic yeast chromosomes and genomes

Astrobiology

In commercial applications

Brewing

Baking

Nutritional yeast

Uses in aquaria

Direct use in medicine

A human pathogen

Invasive and systemic infections

Virulence of different strains

See also

References

Further reading

External links