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'''Saccharomyces''Saccharomyces' is considered a yeast, although this term is historical and ill-defined. ''Saccharomyces'' is a genus of fungus including many species. The distinct species of ''Saccharomyces'' are revised frequently as more research is done. All species are unicellular and capable of fermentation. ''Saccharomyces cerevisiae'' is the most well-known species of yeast. It is used in the fermentation of beer, wine, and sake, and as a leavening agent in bread. It is commonly referred to as "ale yeast", "wine yeast" (see [[Saccharomyces#Killer_Wine_Yeast|Killer Wine Yeast]] below), or "bread yeast". ''S. pastorianus'', known as lager yeast, is a hybrid closely related to ''S. cerevisiae'' but is not a true species. ''S. cerevisiae'' is commonly studied as a model organism and was the first eukaryote to have its genome entirely sequenced. In rare cases, ''Saccharomyces'' can form a [[pellicle]].

''Saccharomyces cerevisiae'' is the type species of the genus ''Saccharomyces'', although ''Saccharomyces paradoxus''and is well-known and highly studied. it is used in industrial production of baking and fermentation as well as bioenergy and biomedical fields. Wholke-genome sequencing was completed in 1996, and since then the body of scientific knowledge on the species of ''S. cerevisiae's'' closest relative, is likely older and more globally ubiquitous higher than any other eukaryotic system. More recently, whole-genome sequencing has also been performed on other species of ''S. cerevisiaeSaccharomyces''. , which has resulted in models for studies on population genomics, as well as insight into the evolution of this genus <ref>ref needed<[https://academic.oup.com/femsyr/article/20/3/foaa013/ref> Many previously recognized species 5810663 Haya Alsammar, Daniela Delneri, An update on the diversity, ecology and biogeography of the Saccharomyces have been consolidated or reassigned to another genus, commonly ''Zygosaccharomyces''FEMS Yeast Research, Volume 20, Issue 3, May 2020, foaa013, https://doi.org/10.1093/femsyr/foaa013.]</ref>.  Species of ''Saccharomyces'' other than ''S. cerevisiae'' (and only certain strains of ''S. cerevisiae'') are generally unable to efficiently ferment maltotriose, although some can ferment maltose (such as ''S. eubayanus'') <ref name="Cubillos_2019">[https://onlinelibrary.wiley.com/doi/10.1002/yea.3380 Bioprospecting for brewers: Exploiting natural diversity for naturally diverse beers. F.A. Cubillos, B. Gibson, N. Grijalva‐Vallejos, K. Krogerus, J. Nikulin. 2019. DOI: https://doi.org/10.1002/yea.3380.]</ref>.

** [https://www.nature.com/articles/s41586-018-0030-5 Genome evolution across 1,011 Saccharomyces cerevisiae isolates, by Peter et al (2018), which indated indicated that domestication of yeast might have begun in Asia.] See also [https://www.theatlantic.com/science/archive/2018/04/yeast-sequencing-china/557930/ this article] and the [https://www.facebook.com/groups/MilkTheFunk/permalink/2056777254350478/ associated MTF thread].** [https://www.nature.com/articles/s41586-020-2889-1 A yeast living ancestor reveals the origin of genomic introgressions.] ''From Dr. Bryan Heit:'' "This study may interest some here. A lot of yeast evolution is driven by introgression - interspecies hybridization which gets "cleaned up" by back-crosses with one of the parental species (but leaving pieces of the other parental species genome behind). But it's always been a bit of a mystery of how these hybrids can back-cross, since these hybrids are usually unable to reproduce sexually. These scientists found a '''living''' ancestor of a hybrid between ''S. cereveseacerevisiae'' and ''S. paradoxus'' that gave rise to many modern ''S. cereveseacerevisiae'' strains, and may have figured out how it regained the ability to reproduce with its parental species <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/4055441394484044 Dr. Bryan Heit. Milk The Funk post on a new study that found a living ancestor of a hybrid between ''S. cereveseacerevisiae'' and ''S. paradoxus'' that gave rise to many modern ''S. cereveseacerevisiae'' strains. 11/12/2020.]</ref>."** [https://www.sciencedaily.com/releases/2019/03/190305153648.htm Modern beer yeast emerged from mix of European grape wine, Asian rice wine yeast, by Science Daily. The two explanations of beer yeast ancestry are: beer yeasts might have evolved from a mix of European wine strains and Asian fermentation strains during trade on the Silk Route, as well as an unknown ancestor. The second explanation is that European wine strains themselves descended from Asian strains (whether European wine strains desceneded descended from Asia or were developed in Europe has not been clear and needs more research).]

** [https://www.nature.com/articles/s41559-019-0998-8 Fermentation innovation through complex hybridization of wild and domesticated yeasts] - Hittinger lab sequencing of commercial and homebrew strains of yeast, analysing analyzing their hybrid species makeup using WGS.

Various other yeast species have the ability to produce toxins that effect a range of other yeasts (but generally not bacteria), including species from the genera ''Candida'', ''Cryptococcus'', ''Debaryomyces'', ''Hanseniaspora'', ''Hansenula'', ''Kluyveromyces'', ''Metschnikowia'', ''Pichia'', ''Ustilago'', ''Torulopsis'', ''Williopsis'', ''Zygosaccharomyces'', ''Aureobasidium'', ''Zygowilliopsis'', and ''Mrakia'' <ref name="Buyuksirit">[http://waset.org/publications/9999528/antimicrobial-agents-produced-by-yeasts Antimicrobial Agents Produced by Yeasts. T. Buyuksirit, H. Kuleasan. 2014.]</ref><ref name="Stewart_2018" />. For example, strains of the yeast species ''Candida pyralidae'' <ref name="Buyuksirit"></ref>, ''Wickerhamomyces anomalus'', ''Kluyveromyces wickeramii'', ''Torulaspora delbrueckii'' and ''Pichia membranifaciens'' have been found to produce toxin that inhibits ''Brettanomyces'' <ref name="Ciani_2016">[https://www.researchgate.net/publication/301581233_Yeast_Interactions_in_Inoculated_Wine_Fermentation Yeast Interactions in Inoculated Wine Fermentation. Maurizio Ciani, Angela Capece, Francesca Comitini, Laura Canonico, Gabriella Siesto and Patrizia Romano. 2016.]</ref><ref>[https://www.mdpi.com/1422-0067/24/2/1309 Agarbati A, Ciani M, Esin S, Agnolucci M, Marcheggiani F, Tiano L, Comitini F. Comparative Zymocidial Effect of Three Different Killer Toxins against Brettanomyces bruxellensis Spoilage Yeasts. International Journal of Molecular Sciences. 2023; 24(2):1309. https://doi.org/10.3390/ijms24021309 .]</ref>. In addition, the toxin produced by ''Wickerhamomyces anomalus'' and ''Williopsis markii'' have been found to inhibit a wide range of spoilage and pathogenic fungi <ref name="Hatoum2012"></ref>. Killer strains of ''S. cerevisiae'' and other yeast can occur naturally in the wild on fruit and can have a negative impact on other flora that are found in the same environment <ref name="Buyuksirit"></ref>. Strains of ''Torulaspora delbrueckii'' have been shown to kill killer strains of ''S. cerevisae'' (wine strains), as well as to kill ''Pichia'' species <ref name="Ciani_2016"></ref>. The occurrence of killer strains of yeast in the wild is also wide spread. For example, out of 210 yeasts from various genera isolated from molasses, 13 of them were killer strains. Out of 1,000 isolates of various ''Candida'' species isolated from human skin, 52 were killer strains. Out of 65 strains of various yeasts isolated from fermented foods, soil samples, and spoiled fruits/vegetables, 12 were killer strains <ref name="Bajaj_2017" />. It has been hypothesized that toxin production is ubiquitous throughout nearly all genera of yeast; the more studies that have been done on a particular genus of yeast, the more likely it is that toxin production has been found by species and strains within that genus. Yeasts that produce toxins have been found on every continent and in every natural habitat of yeast, including leaf surfaces, leaf litter, tree slime fluxes, fruits, cactus stems and cladodes, insect guts, mammal feces, leaf-cutting ant nests, lake water, ocean sediment, soil, wine, bakeries, and dairy products <ref name="Boynton_2019" />.

For a long time the origins of the hybrid were unknown and were postulated to be a hybrid between ''S. cerevisiae'' and ''S.uvarum'', or ''S. cerevisiae'' and ''S.bayanus''. Recent work eg. Libkind et al 2011 proved that the hybridisation was between ''S. eubayanus'', which had been recently found in South America and ''S. cerevisiae'' <ref name="libkind_2011" />. Further work points to a Tibetan lineage of ''S.eubayanus'' being the most likely from those discovered in the wild so far <ref name="bing_2014" /> (see also [https://www.facebook.com/groups/MilkTheFunk/posts/6399366356758191/?comment_id=6399963343365159 this MTF post]). It is hypothesized that the hybridization event occurred in a Bavarian brewery (Hofbräuhaus in Munich has been proposed as the most likely site for the hybridization event) in the 16th century by the chance interaction of ''S. eubayanus'' with ale yeast; however, an alternative hypothesis is that bottom-fermentation with ''S. eubayanus'' was in practice before lager yeast was created <ref>[https://academic.oup.com/femsyr/article/doi/10.1093/femsyr/foad023/7142826 Mathias Hutzler, John P Morrissey, Andreas Laus, Franz Meussdoerffer, Martin Zarnkow, A new hypothesis for the origin of the lager yeast Saccharomyces pastorianus, FEMS Yeast Research, Volume 23, 2023, foad023, https://doi.org/10.1093/femsyr/foad023.]</ref>.

===[[Bootleg Biology]]/[[Spot Yeast]]===