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update to SO2 info
Unlike most genres of yeast, ''Brettanomyces'' has the characteristics of being very tolerant to harsh conditions, including high amounts of alcohol (up to 14.5-15% ABV <ref name="Crauwels1" /><ref name="Agnolucci_2017" />), a pH as low as 2 <ref>[http://www.winesandvines.com/template.cfm?section=news&content=141954 Wines and Vines. New Research on Role of Yeast in Winemaking; report on a presentation by David Mills and Lucy Joseph from UC Davis. 11/14/2014. Retrieved 08/16/2015.]</ref>, and environments with low nitrogen <ref name="Schifferdecker"></ref> and low sugar sources <ref name="Smith_2018">[https://www.sciencedirect.com/science/article/pii/S0740002017308249 The carbon consumption pattern of the spoilage yeast Brettanomyces bruxellensis in synthetic wine-like medium. Brendan D.Smith and Benoit Divol. 2018. DOI: https://doi.org/10.1016/j.fm.2017.12.011.]</ref>. It has been reported that some strains require a very low concentration of fermentable sugars (less than 300 mg/L) and nitrogen (less than 6 mg/L), which is less than most wines contain <ref name="Smith_2017">[https://www.sciencedirect.com/science/article/pii/S0740002017308249 The carbon consumption pattern of the spoilage yeast Brettanomyces bruxellensis in synthetic wine-like medium. Brendan D. Smith, Benoit Divol. 2017.]</ref>. Some strains are able to utilize ethanol, glycerol, acetic acid, and malic acid when no other sugar sources are available <ref name="Smith_2018" />. This capability allows ''Brettanomyces'' to survive in alcoholic beverages such as beer, wine, and cider. In alcoholic beverages, ''B. bruxellensis'' tends to lag after the primary fermentation with ''Saccharomyces''. It is believed that during this lag phase, ''B. bruxellensis'' adapts to the harsh conditions of the beverage (low pH, high concentrations of ethanol, and limited sugar/nitrogen sources). After this lag phase, ''B. bruxellensis'' can grow and survive when no other yeasts can. ''Brettanomyces'' is also more resistant to pH and temperature changes, and tolerant of environments limited in oxygen (although ''Brettanomyces'' prefers the availability of at least a little bit of oxygen). Scientifically, which specific nitrogen and carbon sources ''B. bruxellensis'' uses in these stressful environments has not received much research <ref name="smith_divol_2016"></ref>. [https://www.winesandvines.com/news/article/200000/New-Tools-to-Limit-Wine-Spoilage One study from Dr. Charles Edwards] found that a combination of keeping wine under 54°F (12.2°C) and alcohol at or above 14% resulted in a decline of ''B. bruxellensis'' populations for up to 100 days for two strains that were tested. The study found that neither of the strains grew well at 14% and stopped growth completely at 16% ABV in wine, but one strain grew better than the other at 15%, demonstrating the genetic diversity of ''Brettanomyces''. The researchers concluded that a combination of high ethanol and cold temperatures as well as sulfur dioxide, chitosan, and filtration could be used to control ''Brettanomyces'' in winemaking. ''Brettanomyces'' has been found to be able to grow at temperatures as low as 50°F (10°C) and as high as 95°F (35°C); see [[Brettanomyces#Carbohydrate_Metabolism_and_Fermentation_Temperature|fermentation temperature]] for more information <ref>[http://www.ajevonline.org/content/early/2017/01/05/ajev.2017.16102 Interactions between Storage Temperature and Ethanol that Affect Growth of Brettanomyces bruxellensis in Merlot Wine. Taylor A. Oswald, Charles G. Edwards. 2017.]</ref>.
''Brettanomyces'' is known for not producing much glycerol in beer. [https://en.wikipedia.org/wiki/Glycerol Glycerol] is a colorless, sweet-tasting, viscous liquid that is thought to be an important contributor to the mouthfeel of beer. Glycerol is produced as a stress response by a wide range of microbes, including ''S. cerevisiae'', and various species and strains of ''Debaryomyces'', ''Candida'', ''Lachancea'', and ''Zygosaccharomyces''. Despite not producing amounts of glycerol that are perceivable in beer, some strains of ''Brettanomyces bruxellensis'' actually produce glycerol which is stored inside of their cells as a response to osmotic stress. They can also uptake glycerol into their cells. Doing so allows the cells to survive osmotic pressure <ref>[https://www.sciencedirect.com/science/article/pii/S0740002013001251?via%3Dihub Osmotic stress response in the wine yeast Dekkera bruxellensis. Silvia Galafassi, Marco Toscano, Ileana Vigentin, Jure Piškur, Concetta Compagno. 2013.]</ref><ref>[https://academic.oup.com/femsle/advance-article-abstract/doi/10.1093/femsle/fny020/4828327?redirectedFrom=fulltext Osmotolerance of Dekkera bruxellensis and the role of two Stl glycerol-proton symporters. Jana Zemančíková, Michala Dušková, Hana Elicharová, Klára Papoušková, Hana Sychrová. 2018.]</ref>. It is currently not known how many strains are capable of producing glycerol internally, or if this amount of glycerol has any impact on perceived mouthfeel of a beer if a substantial amount of ''Brettanomyces'' cells eventually autolyze (see [https://www.facebook.com/groups/MilkTheFunk/permalink/2003626776332193/ this MTF thread]). The role of glycerol in creating mouthfeel is debatable in the wine world <ref>[https://www.winesandvines.com/features/article/68760 Tim Patterson. "Many Roads to Mouthfeel". Wines & Vines Magazine. Nov 2009. Retrieved 03/23/2018.]</ref>.
The genetic diversity of ''Brettanomyces'' is particularly wide. Some studies have indicated that strains of ''B. bruxellensis'' have adapted to specific environments. For example, one study found that strains of ''B. bruxellensis'' isolated from wine had 20 genes involved in the metabolism of carbon and nitrogen, whereas strains isolated from beer did not. This indicated that ''B. bruxellensis'' strains living in wine have adapted to the harsher environment of wine <ref name="smith_divol_2016"></ref>. Another study found that one out of the two strains tested that were isolated from soda could not ferment maltose, and only strains isolated from wine were able to grow in wine and the beer/soda strains did not. The wine strains were also more resistant to sulfites, which are commonly used in the wine industry to prevent microbial contamination <ref name="Crauwels_2016" />.
A genetic survey of 1488 different strains of ''B. bruxellensis'' from 29 countries, 5 continents, and 9 different fermentation niches was conducted in 2018 by Avramova et al. They found that these strains formed roughly 5 genetic groups with mostly separate ancestral lineages, and 1 group with a mixed ancestral lineage: 3 wine groups, 1 beer group, 1 kombucha group (most distantly related to the beer group), as well as 1 tequila/ethanol group that has multiple ancestral lineages. This was expressed mostly in the ploidy level of each group (the number of sets of chromosomes), with 2 of the wine groups, the tequila group, and the beer group containing more sets of chromosome pairs than the other groups (diploid vs triploid; this is thought to encourage adaption and hybridization). Additionally, the triploid wine group was generally more tolerant of SO<sup>2</sup> than the diploid wine groups. The genetic differences between the fermentation substrates (beer, wine, etc.) were lower but still significant, and this was explained by the frequent cross-over of equipment such as wine barrels being used for beer fermentation. When comparing the geographic differences, they found geography contributed only 5% of genetic differences, while geography explained more than 50% of genetic differences in non-wine strains, suggesting that beer, kombucha, and tequila strains are more localized genetically than wine strains and that humans probably helped the wine strains travel across the globe. They also found that although one study reported spore-forming versions of ''B. bruxellensis'' (referred to as ''Dekkera bruxellensis''), the genetic makeup of the analyzed strains determined their ability to sporulate to be non-existent or rare (only one study that we know of by [https://link.springer.com/article/10.1007%2FBF02539015 Walt and Kerken in 1960] has reported sporulation in ''Brettanomyces'' only on specific agar types with vitamins added, indicating that sporulation in ''Brettanomyces'' is extremely rare) <ref name="Avramova_2018" />. See also [https://www.facebook.com/groups/MilkTheFunk/permalink/2022801681081369/ Richard Preiss's discussion of this study on MTF].
Sulfite and SO<sub>2</sub> inhibits the growth of ''Brettanomyces'', and is often used in the wine industry to prevent the growth of ''Brettanomyces'' (some wineries have identified small amounts of flavors from ''Brettanomyces'' as being beneficial to certain wine styles, and is said to increase the complexity and impart an aged character in young wines <ref name="smith_divol_2016"></ref>) <ref>[http://onlinelibrary.wiley.com/doi/10.1111/j.1745-4549.2012.00702.x/abstract Removal of Brettanomyces Bruxellensis from Red Wine Using Membrane Filtration. Umiker, Descenzo, Lee, and Edwards. 04/24/2012.]</ref>. However, it has been shown that wine strains of ''B. bruxellensis'' could survive dosages of up to 1 mg/L of molecular SO<sub>2</sub>, and the very high dosage of 2.1 mg/L was needed to kill ''Brettanomyces'' in wine <ref name="Agnolucci_2017" />. This dosage of molecular SO<sub>2</sub> requires a total amount of SO<sub>2</sub> that is beyond legal limits (350 mg/l <ref>[https://grapesandwine.cals.cornell.edu/sites/grapesandwine.cals.cornell.edu/files/shared/documents/Research-Focus-2011-3.pdf Sulphur Dioxide Content of Wines: the Role of Winemaking and Carbonyl Compounds. Nick Jackowetz, Erhu Li, and Ramón Mira de Orduña. 2011.]</ref>; see this [https://grapesandwine.cals.cornell.edu/newsletters/appellation-cornell/2012-newsletters/issue-12/article-contains-sulfites/ Cornell University] blog post that explains the difference between ''free'' and ''molecular'' SO<sub>2</sub>) and has negative effects on wine. One study found that out of 145 strains of ''B. bruxellensis'', 107 of which were wine strains with the rest being from beer, tequila, kombucha, etc., 36% of them were either tolerant (lagged growth, but achieved full growth eventually) or resistant (no lagged growth, and achieved full growth) of 0.6 mg/L of molecular SO<sub>2</sub>. 46 of the 52 resistant/tolerant strains were wine strains, thus demonstrating that wine strains of ''B. bruxellensis'' are generally more tolerant of SO<sub>2</sub> than strains of ''B. bruxellensis'' that are found in other types of beverages. It is thought that the wine strains have adapted to the conditions of winemakers adding SO<sub>2</sub> to wine <ref>[https://www.frontiersin.org/articles/10.3389/fmicb.2018.01260/full Molecular Diagnosis of Brettanomyces bruxellensis’ Sulfur Dioxide Sensitivity Through Genotype Specific Method. Avramova M, Vallet-Courbin A, Maupeu J, Masneuf-Pomarède I, Albertin W. 2018. DOI: 10.3389/fmicb.2018.01260.]</ref>. Some strains of ''Candida pyralidae'', ''Wickerhamomyces anomalus'', ''Kluyveromyces wickeramii'', ''Torulaspora delbrueckii'' and ''Pichia membranifaciens'' have been found to produce toxin that inhibits ''Brettanomyces'', and these toxins have been proposed as an alternative to SO<sub>2</sub> as a way to kill ''Brettanomyces'' (killer wine strains of ''Saccharomyces cerevisiae'' do not kill ''Brettanomyces''; see [[Saccharomyces#Killer_Wine_Yeast|Killer Wine Yeast]] for more information). [http://www.laboratoriosenosan.com/en/effectiveness-of-kaolin-silver-complex/ Kaolin silver complex (KAgC)] has been found to inhibit ''Brettanomyces'' and acetic acid bacteria in wine when used in legal dosages, and has been proposed as a replacement for SO<sub>2</sub> or to minimize the use of SO<sub>2</sub> <ref>[https://www.ncbi.nlm.nih.gov/pubmed/29666535?dopt=Abstract Effect of kaolin silver complex on the control of populations of Brettanomyces and acetic acid bacteria in wine. Izquierdo-Cañas PM, López-Martín R, García-Romero E, González-Arenzana L, Mínguez-Sanz S, Chatonnet P, Palacios-García A, Puig-Pujol A. 2018. DOI: 10.1007/s13197-018-3097-y.]</ref>. Other proposed replacements for SO<sub>2</sub> as a way to inhibit ''Brettanomyces'' in wine include [https://en.wikipedia.org/wiki/Pascalization high pressure processing] and [https://www.sciencedirect.com/science/article/abs/pii/S0255270106001929 pulsed electric fields] <ref>[https://www.sciencedirect.com/science/article/pii/S1466856418302972 SO2, high pressure processing and pulsed electric field treatments of red wine: Effect on sensory, Brettanomyces inactivation and other quality parameters during one year storage. Sanelle Van Wyk, Mohammed M. Farid, Filipa V.M. Silva. 2018. DOI: https://doi.org/10.1016/j.ifset.2018.06.016.]</ref>.
The addition of vitamins can have a positive impact on ''Brettanomyces'' growth. For example, while ''Brettanomyces'' does not need riboflavin (vitamin B2) or thiamine (vitamin B1) in order to grow, the presence of either or both of these two vitamins encourages ''Brettanomyces'' growth <ref>[http://onlinelibrary.wiley.com/doi/10.1002/jib.385/full The influence of thiamine and riboflavin on various spoilage microorganisms commonly found in beer. Barry Hucker, Melinda Christophersen, Frank Vriesekoop. 2017.]</ref>. Other vitamins such as p-aminobenzoic acid (PABA), folic acid (vitamin B9), nicotinic acid (vitamin B3), pantothenic acid (vitamin B5) are also not required for most strains of ''Brettanomyces'' to grow. The presence of alcohol can increase the dependence on vitamins for some strains of ''Brettanomyces'' to grow. For example, Myo-inositol (vitamin B8) and thiamine (vitamin B1) were required by two strains of ''B. bruxellensis'' when grown in 10% ethanol but not in 0% ethanol. Biotin (vitamin B7) is the one exception, and it was found that the lack of biotin inhibited the growth of some strains of ''B. bruxellensis''. Other studies contradict these previously mentioned findings, showing that thiamine was not required by the strains of ''B. bruxellensis'' tested, that pyridoxine was required, and biotin was not required. These discrepancies between scientific studies are probably due to the genetic differences between the strains selected, the growth media chosen by the scientists, and/or the growth conditions <ref>[http://www.mdpi.com/2311-5637/2/3/17 Use of Nutritional Requirements for Brettanomyces bruxellensis to Limit Infections in Wine. Nicolas H. von Cosmos and Charles G. Edwards. 2016.]</ref>.