Yeasts areeukaryotic, single-celledmicroorganisms classified as members of thefunguskingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500species are currently recognized.[1][2][3] They are estimated to constitute 1% of all described fungal species.[4]
Some yeast species have the ability to develop multicellular characteristics by forming strings of connected budding cells known aspseudohyphae or falsehyphae, or quickly evolve into amulticellular cluster with specialisedcell organelles function.[5][6] Yeast sizes vary greatly, depending on species and environment, typically measuring 3–4 μm indiameter, although some yeasts can grow to 40 μm in size.[7] Most yeasts reproduceasexually bymitosis, and many do so by the asymmetric division process known asbudding. With their single-celled growth habit, yeasts can be contrasted withmolds, which growhyphae. Fungal species that can take both forms (depending on temperature or other conditions) are calleddimorphic fungi.
Yeasts do not form a singletaxonomic orphylogenetic grouping. The term "yeast" is often taken as asynonym forSaccharomyces cerevisiae,[11] but the phylogenetic diversity of yeasts is shown by their placement in two separatephyla: theAscomycota and theBasidiomycota. The budding yeasts or "true yeasts" are classified in theorderSaccharomycetales,[12] within the phylum Ascomycota.
The word "yeast" comes fromOld Englishgist,gyst, and from theIndo-European rootyes-, meaning "boil", "foam", or "bubble".[13] Yeast microbes are probably one of the earliestdomesticated organisms. Archaeologists digging inEgyptian ruins found earlygrinding stones and baking chambers for yeast-raised bread, as well as drawings of 4,000-year-old bakeries andbreweries.[14] Vessels studied from several archaeological sites inIsrael (dating to around 5,000, 3,000 and 2,500 years ago), which were believed to have contained alcoholic beverages (beer andmead), were found to contain yeast colonies that had survived over the millennia, providing the first direct biological evidence of yeast use in early cultures.[15] In 1680,Dutch naturalistAnton van Leeuwenhoek firstmicroscopically observed yeast, but at the time did not consider them to beliving organisms, but rather globular structures[16] as researchers were doubtful whether yeasts werealgae or fungi.[17]Theodor Schwann recognized them as fungi in 1837.[18][19]
In 1857, French microbiologistLouis Pasteur showed that by bubbling oxygen into the yeast broth,cell growth could be increased, but fermentation was inhibited – an observation later called the "Pasteur effect". In the paper "Mémoire sur la fermentation alcoolique," Pasteur proved that alcoholic fermentation was conducted by living yeasts and not by a chemical catalyst.[14][20]
By the late 18th century two yeast strains used in brewing had been identified:Saccharomyces cerevisiae (top-fermenting yeast) andS. pastorianus (bottom-fermenting yeast).S. cerevisiae has been sold commercially by the Dutch for bread-making since 1780; while, around 1800, the Germans started producingS. cerevisiae in the form of cream. In 1825, a method was developed to remove the liquid so the yeast could be prepared as solid blocks.[21] The industrial production of yeast blocks was enhanced by the introduction of thefilter press in 1867. In 1872, BaronMax de Springer developed a manufacturing process to create granulated yeast frombeetrootmolasses,[22][23][24] a technique that was used until the first World War.[25] In the United States, naturally occurring airborne yeasts were used almost exclusively until commercial yeast was marketed at theCentennial Exposition in 1876 in Philadelphia, whereCharles L. Fleischmann exhibited the product and a process to use it, as well as serving the resultant baked bread.[26]
Themechanical refrigerator (first patented in the 1850s in Europe) liberatedbrewers andwinemakers from seasonal constraints for the first time and allowed them to exit cellars and other earthen environments. ForJohn Molson, who made his livelihood inMontreal prior to the development of the fridge, the brewing season lasted from September through to May. The same seasonal restrictions formerly governed thedistiller's art.[27]
Yeasts vary in regard to the temperature range in which they grow best. For example,Leucosporidium frigidum grows at −2 to 20 °C (28 to 68 °F),Saccharomyces telluris at 5 to 35 °C (41 to 95 °F), andCandida slooffi at 28 to 45 °C (82 to 113 °F).[29] The cells can survive freezing under certain conditions, with viability decreasing over time.
In general, yeasts are grown in the laboratory on solidgrowth media or in liquidbroths. Common media used for the cultivation of yeasts includepotato dextrose agar orpotato dextrose broth, Wallerstein Laboratories nutrientagar, yeastpeptonedextrose agar, and yeast mould agar or broth. Home brewers who cultivate yeast frequently use driedmalt extract and agar as a solid growth medium. Thefungicidecycloheximide is sometimes added to yeast growth media to inhibit the growth ofSaccharomyces yeasts and select for wild/indigenous yeast species. This will change the yeast process.
The appearance of a white, thready yeast, commonly known askahm yeast, is often a byproduct of the lactofermentation (or pickling) of certain vegetables. It is usually the result of exposure to air. Although harmless, it can give pickled vegetables a bad flavor and must be removed regularly during fermentation.[30]
Ecology
Yeasts are very common in the environment, and are often isolated from sugar-rich materials. Examples include naturally occurring yeasts on the skins of fruits and berries (such as grapes, apples, orpeaches), andexudates from plants (such as plant saps or cacti). Some yeasts are found in association with soil and insects.[31][32] Yeasts from the soil and from the skins of fruits and berries have been shown to dominate fungalsuccession during fruit decay.[33] The ecological function andbiodiversity of yeasts are relatively unknown compared to those of othermicroorganisms.[34] Yeasts, includingCandida albicans,Rhodotorula rubra,Torulopsis andTrichosporon cutaneum, have been found living in between people's toes as part of theirskin flora.[35] Yeasts are also present in thegut flora of mammals and some insects[36] and even deep-sea environments host an array of yeasts.[37][38]
An Indian study of sevenbee species and nine plant species found 45 species from 16 genera colonize thenectaries of flowers and honey stomachs of bees. Most were members of the genusCandida; the most common species in honey stomachs wasDekkera intermedia and in flower nectaries,Candida blankii.[39] Yeast colonising nectaries of thestinking hellebore have been found to raise the temperature of the flower, which may aid in attracting pollinators by increasing the evaporation ofvolatile organic compounds.[34][40] Ablack yeast has been recorded as a partner in a complex relationship betweenants, theirmutualistic fungus, a fungalparasite of the fungus and a bacterium that kills the parasite. The yeast has a negative effect on the bacteria that normally produce antibiotics to kill the parasite, so may affect the ants' health by allowing the parasite to spread.[41]
Certain strains of some species of yeasts produce proteins called yeast killer toxins that allow them to eliminate competing strains. (See main article onkiller yeast.) This can cause problems for winemaking but could potentially also be used to advantage by using killer toxin-producing strains to make the wine. Yeast killer toxins may also have medical applications in treating yeast infections (see "Pathogenic yeasts" section below).[42]
Marine yeasts, defined as the yeasts that are isolated from marine environments, are able to grow better on a medium prepared using seawater rather than freshwater.[43] The first marine yeasts were isolated by Bernhard Fischer in 1894 from theAtlantic Ocean, and those were identified asTorula sp. andMycoderma sp.[44] Following this discovery, various other marine yeasts have been isolated from around the world from different sources, including seawater, seaweeds, marine fish and mammals.[45] Among these isolates, some marine yeasts originated from terrestrial habitats (grouped as facultative marine yeast), which were brought to and survived in marine environments. The other marine yeasts were grouped as obligate or indigenous marine yeasts, which are confined to marine habitats.[44] However, no sufficient evidence has been found to explain the indispensability of seawater for obligate marine yeasts.[43] It has been reported that marine yeasts are able to produce many bioactive substances, such as amino acids, glucans, glutathione, toxins, enzymes, phytase, and vitamins with potential applications in the food, pharmaceutical, cosmetic, and chemical industries as well as for marine culture and environmental protection.[43] Marine yeast was successfully used to produce bioethanol using seawater-based media which will potentially reduce thewater footprint of bioethanol.[46]
Yeasts, like all fungi, may haveasexual andsexual reproductive cycles. The most common mode of vegetative growth in yeast is asexual reproduction bybudding,[47] where a small bud (also known as ableb or daughter cell) is formed on the parent cell. Thenucleus of the parent cell splits into a daughter nucleus and migrates into the daughter cell. The bud then continues to grow until it separates from the parent cell, forming a new cell.[48] The daughter cell produced during the budding process is generally smaller than the mother cell. Some yeasts, includingSchizosaccharomyces pombe, reproduce byfission instead of budding,[47] and thereby creating two identically sized daughter cells.
In general, under high-stress conditions such asnutrient starvation,haploid cells will die; under the same conditions, however,diploid cells can undergo sporulation, entering sexual reproduction (meiosis) and producing a variety of haploidspores, which can go on tomate (conjugate), reforming the diploid.[49]
The haploid fission yeastSchizosaccharomyces pombe is a facultative sexual microorganism that can undergo mating when nutrients are limited.[3][50] Exposure ofS. pombe to hydrogen peroxide, an agent that causes oxidative stress leading to oxidative DNA damage, strongly induces mating and the formation of meiotic spores.[51] The budding yeastSaccharomyces cerevisiae reproduces by mitosis as diploid cells when nutrients are abundant, but when starved, this yeast undergoes meiosis to form haploid spores.[52] Haploid cells may then reproduce asexually by mitosis. Katz Ezov et al.[53] presented evidence that in naturalS. cerevisiae populations clonal reproduction and selfing (in the form of intratetrad mating) predominate. In nature, the mating of haploid cells to form diploid cells is most often between members of the same clonal population andout-crossing is uncommon.[54] Analysis of the ancestry of naturalS. cerevisiae strains led to the conclusion that out-crossing occurs only about once every 50,000 cell divisions.[54] These observations suggest that the possible long-term benefits of outcrossing (e.g. generation of diversity) are likely to be insufficient for generally maintaining sex from one generation to the next.[citation needed] Rather, a short-term benefit, such as recombinational repair during meiosis,[55] may be the key to the maintenance of sex inS. cerevisiae.
Alcoholic beverages are defined asbeverages that containethanol (C2H5OH). This ethanol is almost always produced byfermentation – themetabolism ofcarbohydrates by certain species of yeasts under anaerobic or low-oxygen conditions. Beverages such as mead, wine, beer, ordistilled spirits all use yeast at some stage of their production. A distilled beverage is a beverage containing ethanol that has been purified bydistillation. Carbohydrate-containing plant material is fermented by yeast, producing a dilute solution of ethanol in the process. Spirits such aswhiskey andrum are prepared by distilling these dilute solutions of ethanol. Components other than ethanol are collected in the condensate, including water,esters, and other alcohols, which (in addition to that provided by the oak in which it may be aged) account for theflavour of the beverage.
Yeast ring used by Swedish farmhouse brewers in the 19th century to preserve yeast between brewing sessions.Bubbles ofcarbon dioxide forming during beer-brewing[9]
Brewing yeasts may be classed as "top-cropping" (or "top-fermenting") and "bottom-cropping" (or "bottom-fermenting").[59] Top-cropping yeasts are so called because they form a foam at the top of thewort during fermentation. An example of a top-cropping yeast isSaccharomyces cerevisiae, sometimes called an "ale yeast".[60] Bottom-cropping yeasts are typically used to producelager-type beers, though they can also produceale-type beers. These yeasts ferment well at low temperatures. An example of bottom-cropping yeast isSaccharomyces pastorianus, formerly known asS. carlsbergensis.
Decades ago,[vague] taxonomists reclassifiedS. carlsbergensis (uvarum) as a member ofS. cerevisiae, noting that the only distinct difference between the two is metabolic.[dubious –discuss] Lager strains ofS. cerevisiae secrete an enzyme called melibiase, allowing them to hydrolysemelibiose, adisaccharide, into more fermentablemonosaccharides. Top- and bottom-cropping and cold- and warm-fermenting distinctions are largely generalizations used by laypersons to communicate to the general public.[61]
The most common top-cropping brewer's yeast,S. cerevisiae, is the same species as the common baking yeast.[62] Brewer's yeast is also very rich inessential minerals and theB vitamins (except B12), a feature exploited in food products made from leftover (by-product) yeast from brewing.[63] However, baking and brewing yeasts typically belong to different strains, cultivated to favour different characteristics: baking yeast strains are more aggressive, to carbonatedough in the shortest amount of time possible; brewing yeast strains act more slowly but tend to produce fewer off-flavours and tolerate higher alcohol concentrations (with some strains, up to 22%).
Dekkera/Brettanomyces is a genus of yeast known for its important role in the production of 'lambic' and specialtysour ales, along with the secondary conditioning of a particular BelgianTrappist beer.[64] The taxonomy of the genusBrettanomyces has been debated since its early discovery and has seen many reclassifications over the years. Early classification was based on a few species that reproduced asexually (anamorph form) through multipolar budding.[65] Shortly after, the formation of ascospores was observed and the genusDekkera, which reproduces sexually (teleomorph form), was introduced as part of the taxonomy.[66] The current taxonomy includes five species within the genera ofDekkera/Brettanomyces. Those are the anamorphsBrettanomyces bruxellensis,Brettanomyces anomalus,Brettanomyces custersianus,Brettanomyces naardenensis, andBrettanomyces nanus, with teleomorphs existing for the first two species,Dekkera bruxellensis andDekkera anomala.[67] The distinction betweenDekkera andBrettanomyces is arguable, with Oelofse et al. (2008) citing Loureiro and Malfeito-Ferreira from 2006 when they affirmed that current molecular DNA detection techniques have uncovered no variance between the anamorph and teleomorph states. Over the past decade,Brettanomyces spp. have seen an increasing use in the craft-brewing sector of the industry, with a handful of breweries having produced beers that were primarily fermented with pure cultures ofBrettanomyces spp. This has occurred out of experimentation, as very little information exists regarding pure culture fermentative capabilities and the aromatic compounds produced by various strains.Dekkera/Brettanomyces spp. have been the subjects of numerous studies conducted over the past century, although a majority of the recent research has focused on enhancing the knowledge of the wine industry. Recent research on eightBrettanomyces strains available in the brewing industry focused on strain-specific fermentations and identified the major compounds produced during pure culture anaerobic fermentation in wort.[68]
Yeast is used inwinemaking, where it converts the sugars present (glucose andfructose) ingrape juice (must) into ethanol. Yeast is normally already present on grape skins.Fermentation can be done with this endogenous "wild yeast",[69] but this procedure gives unpredictable results, which depend upon the exact types of yeast species present. For this reason, a pure yeast culture is usually added to the must; this yeast quickly dominates the fermentation. The wild yeasts are repressed, which ensures a reliable and predictable fermentation.[70]
Most added wine yeasts are strains ofS. cerevisiae, though not all strains of the species are suitable.[70] DifferentS. cerevisiae yeast strains have differing physiological and fermentative properties, therefore the actual strain of yeast selected can have a direct impact on the finished wine.[71] Significant research has been undertaken into the development of novel wine yeast strains that produce atypical flavour profiles or increased complexity in wines.[72][73]
The growth of some yeasts, such asZygosaccharomyces andBrettanomyces, in wine can result inwine faults and subsequent spoilage.[74]Brettanomyces produces an array ofmetabolites when growing in wine, some of which are volatilephenolic compounds. Together, these compounds are often referred to as "Brettanomyces character", and are often described as "antiseptic" or "barnyard" type aromas.Brettanomyces is a significant contributor to wine faults within the wine industry.[75]
Researchers from theUniversity of British Columbia, Canada, have found a new strain of yeast that has reducedamines. The amines inred wine andChardonnay produce off-flavors and cause headaches and hypertension in some people. About 30% of people are sensitive to biogenic amines, such ashistamines.[76]
Yeast, most commonlyS. cerevisiae, is used in baking as aleavening agent, converting thefermentable sugars present in dough intocarbon dioxide. This causes the dough to expand or rise as gas forms pockets or bubbles. When the dough is baked, the yeast dies and the air pockets "set", giving the baked product a soft and spongy texture. The use of potatoes, water from potato boiling,eggs, or sugar in a bread dough accelerates the growth of yeast. Most yeasts used in baking are of the same species common in alcoholic fermentation. In addition,Saccharomyces exiguus (also known asS. minor), a wild yeast found on plants, fruits, and grains, is occasionally used for baking. In breadmaking, the yeast initially respires aerobically, producing carbon dioxide and water. When the oxygen is depleted,fermentation begins, producing ethanol as a waste product; however, this evaporates during baking.[77]
A block of compressed fresh yeast
It is not known when yeast was first used to bake bread. The first records that show this use came fromAncient Egypt.[8] Researchers speculate a mixture of flour meal and water was left longer than usual on a warm day and the yeasts that occur in natural contaminants of theflour caused it to ferment before baking. The resulting bread would have been lighter and tastier than the normal flat, hard cake.
Active dried yeast, a granulated form in which yeast is commercially sold
Today, there are several retailers of baker's yeast; one of the earlier developments in North America isFleischmann's Yeast, in 1868. During World War II, Fleischmann's developed agranulated active dry yeast which did not require refrigeration, had a longershelf life than fresh yeast, and rose twice as fast. Baker's yeast is also sold as a fresh yeast compressed into a square "cake". This form perishes quickly, so must be used soon after production. A weak solution of water and sugar can be used to determine whether yeast is expired.[78] In the solution, active yeast will foam and bubble as it ferments the sugar into ethanol and carbon dioxide. Some recipes refer to this asproofing the yeast, as it "proves" (tests) the viability of the yeast before the other ingredients are added. When asourdough starter is used, flour and water are added instead of sugar; this is referred to as proofing thesponge.[citation needed]
When yeast is used for making bread, it is mixed withflour, salt, and warm water or milk. The dough iskneaded until it is smooth, and then left to rise, sometimes until it has doubled in size. The dough is then shaped into loaves. Some bread doughs are knocked back after one rising and left to rise again (this is calleddough proofing) and then baked. A longer rising time gives a better flavor, but the yeast can fail to raise the bread in the final stages if it is left for too long initially.[citation needed]
Bioremediation
Some yeasts can find potential application in the field ofbioremediation. One such yeast,Yarrowia lipolytica, is known to degradepalm oil milleffluent,TNT (an explosive material), and otherhydrocarbons, such asalkanes,fatty acids, fats and oils.[79] It can also tolerate high concentrations of salt andheavy metals,[80] and is being investigated for its potential as a heavy metalbiosorbent.[81]Saccharomyces cerevisiae has potential to bioremediate toxic pollutants likearsenic from industrial effluent.[82] Bronze statues are known to be degraded by certain species of yeast.[83] Different yeasts from Brazilian gold minesbioaccumulate free andcomplexed silver ions.[84]
The ability of yeast to convert sugar into ethanol has been harnessed by the biotechnology industry to produceethanol fuel. The process starts by milling a feedstock, such assugar cane,field corn, or othercereal grains, and then adding dilutesulfuric acid, or fungal alphaamylase enzymes, to break down the starches into complex sugars. A glucoamylase is then added to break the complex sugars down into simple sugars. After this, yeasts are added to convert the simple sugars to ethanol, which is then distilled off to obtain ethanol up to 96% in purity.[85]
Saccharomyces yeasts have beengenetically engineered to fermentxylose, one of the major fermentable sugars present incellulosic biomasses, such as agriculture residues, paper wastes, and wood chips.[86][87] Such a development means ethanol can be efficiently produced from more inexpensive feedstocks, makingcellulosic ethanol fuel a more competitively priced alternative to gasoline fuels.[88]
A number of sweetcarbonated beverages can be produced by the same methods as beer, except the fermentation is stopped sooner, producing carbon dioxide, but only trace amounts of alcohol, leaving a significant amount of residual sugar in the drink.
Yeast is used as an ingredient in foods for itsumami flavor, in much of the same way thatmonosodium glutamate (MSG) is used and, like MSG, yeast often contains freeglutamic acid. Examples include:[92]
Yeast extract, made from the intracellular contents of yeast and used asfood additives orflavours. The general method for making yeast extract for food products such asVegemite andMarmite on a commercial scale isheat autolysis, i.e. to add salt to a suspension of yeast, making the solution hypertonic, which leads to the cells' shrivelling up. This triggersautolysis, wherein the yeast'sdigestive enzymes break their ownproteins down into simpler compounds, a process of self-destruction. The dying yeast cells are then heated to complete their breakdown, after which the husks (yeast with thick cell walls that would give poor texture) are removed. Yeast autolysates are used inVegemite andPromite (Australia);Marmite (the United Kingdom); the unrelatedMarmite (New Zealand);Vitam-R (Germany); andCenovis (Switzerland).
Nutritional yeast flakes are yellow in colourNutritional yeast, which is whole dried, deactivated yeast cells, usuallyS. cerevisiae. Usually in the form of yellow flake or powder, its nutty and umami flavor makes it a vegan substitute forcheese powder.[93] Another popular use is as a topping for popcorn. It can also be used in mashed and fried potatoes, as well as inscrambled eggs. It comes in the form of flakes, or as a yellow powder similar in texture tocornmeal. In Australia, it is sometimes sold as "savoury yeast flakes".[94]
Both types of yeast foods above are rich inB-complex vitamins (besides vitamin B12 unless fortified),[63] making them an attractive nutritional supplement to vegans.[93] The same vitamins are also found in some yeast-fermented products mentioned above, such askvass.[95] Nutritional yeast in particular is naturally low in fat andsodium and a source of protein and vitamins as well as other minerals andcofactors required for growth. Many brands of nutritional yeast and yeast extract spreads, though not all, are fortified withvitamin B12, which is produced separately bybacteria.[96]
In 1920, theFleischmann Yeast Company began to promote yeast cakes in a "Yeast for Health" campaign. They initially emphasized yeast as a source of vitamins, good for skin and digestion. Their later advertising claimed a much broader range of health benefits, and was censured as misleading by theFederal Trade Commission. Thefad for yeast cakes lasted until the late 1930s.[97]
Yeast is often used byaquarium hobbyists to generate carbon dioxide (CO2) to nourish plants inplanted aquaria.[102] CO2 levels from yeast are more difficult to regulate than those from pressurized CO2 systems. However, the low cost of yeast makes it a widely used alternative.[102]
On 24 April 1996,S. cerevisiae was announced to be the first eukaryote to have itsgenome, consisting of 12 millionbase pairs, fully sequenced as part of theGenome Project.[106] At the time, it was the most complex organism to have its full genome sequenced, and the work of seven years and the involvement of more than 100 laboratories to accomplish.[107] The second yeast species to have its genome sequenced wasSchizosaccharomyces pombe, which was completed in 2002.[108][109] It was the sixth eukaryotic genome sequenced and consists of 13.8 million base pairs. As of 2014, over 50 yeast species have had their genomes sequenced and published.[110]
Various yeast species have been genetically engineered to efficiently produce various drugs, a technique calledmetabolic engineering.[115]S. cerevisiae is easy to genetically engineer; its physiology, metabolism and genetics are well known, and it is amenable for use in harsh industrial conditions. A wide variety of chemical in different classes can be produced by engineered yeast, includingphenolics,isoprenoids,alkaloids, andpolyketides.[116] About 20% ofbiopharmaceuticals are produced inS. cerevisiae, includinginsulin,vaccines forhepatitis, andhuman serum albumin.[117]
Gram stain ofCandida albicans from a vaginal swab. The small oval chlamydospores are 2–4μm in diameter.Aphotomicrograph ofCandida albicans showing hyphal outgrowth and other morphological characteristics
Yeasts are able to grow in foods with a low pH (5.0 or lower) and in the presence of sugars, organic acids, and other easily metabolized carbon sources.[123] During their growth, yeasts metabolize some food components and produce metabolic end products. This causes the physical, chemical, and sensible properties of a food to change, and the food is spoiled.[124] The growth of yeast within food products is often seen on their surfaces, as in cheeses or meats, or by the fermentation of sugars in beverages, such as juices, and semiliquid products, such assyrups andjams.[123] The yeast of the genusZygosaccharomyces have had a long history as spoilage yeasts within thefood industry. This is mainly because these species can grow in the presence of high sucrose, ethanol,acetic acid,sorbic acid,benzoic acid, andsulfur dioxide concentrations,[74] representing some of the commonly usedfood preservation methods.Methylene blue is used to test for the presence of live yeast cells.[125] Inoenology, the major spoilage yeast isBrettanomyces bruxellensis.
An Indian study of sevenbee species and nine plant species found 45 yeast species from 16 genera colonise thenectaries of flowers and honey stomachs of bees. Most were members of the genusCandida; the most common species in honey bee stomachs wasDekkera intermedia, while the most common species colonising flower nectaries wasCandida blankii. Although the mechanism is not fully understood, it was found thatA. indica flowers more ifCandida blankii is present.[39]
In another example,Spathaspora passalidarum, found in the digestive tract ofbess beetles, aids the digestion of plant cells by fermentingxylose.[127]
Manyfruits produce different types of sugars that attract yeasts, which ferment the sugar and turns it into alcohol. Fruit eating mammals find the scent of alcohol attractive as it indicates a ripe, sugary fruit which provides more nutrition. In turn, the mammals helps disperse both the fruit's seeds and the yeast's spores.[128][129]
Yeast andsmall hive beetle have mutualistic relationship. While small hive beetle is attracted by the pheromone released by the host honeybee, yeast can produce a similar pheromone which have the same attractive effect to the small hive beetle. Therefore, yeast facilitates SHB's infestation if the beehive contains yeast inside.[130]
^Piškur, Jure; Compagno, Concetta (2014).Molecular Mechanisms in Yeast Carbon Metabolism. Springer. p. 98.ISBN978-3-642-55013-3.The second completely sequenced yeast genome came 6 years later from the fission yeastSchizosaccharomyces pombe, which diverged fromS. cerevisiae probably more than 300 million years ago.
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^Kurtzman CP, Fell JW (2005). Gábor P, de la Rosa CL (eds.).Biodiversity and Ecophysiology of Yeasts. The Yeast Handbook. Berlin: Springer. pp. 11–30.ISBN978-3-540-26100-1.
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^abRuderfer DM, Pratt SC, Seidel HS, Kruglyak L (2006). "Population genomic analysis of outcrossing and recombination in yeast".Nature Genetics.38 (9):1077–1081.doi:10.1038/ng1859.PMID16892060.S2CID783720.
^Birdsell JA, Wills C (2003). MacIntyre RJ, Clegg MT (eds.).The evolutionary origin and maintenance of sexual recombination: A review of contemporary models. Evolutionary Biology Series >> Evolutionary Biology. Vol. 33. Springer. pp. 27–137.ISBN978-0306472619.
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^Hurley R, de Louvois J, Mulhall A (1987). "Yeast as human and animal pathogens". In Rose AH, Harrison JS (eds.).The Yeasts. Volume 1: Biology of Yeasts (2nd ed.). New York, New York:Academic Press. pp. 207–281.
^abKurtzman CP (2006). "Detection, identification and enumeration methods for spoilage yeasts". In Blackburn CDW (ed.).Food spoilage microorganisms. Cambridge, England:Woodhead Publishing. pp. 28–54.ISBN978-1-85573-966-6.
^Fleet GH, Praphailong W (2001). "Yeasts". In Moir CJ (ed.).Spoilage of Processed Foods: Causes and Diagnosis. Food Microbiology Group of the Australian Institute of Food Science and Technology (AIFST). pp. 383–397.ISBN978-0-9578907-0-1.
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