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updated killer toxin of Saccharomyces eubayanus
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>. 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" />.
Scientists have used genetic modification to create ''S. cerevisiae'' strains that produce various killer toxins that can assist in completing fermentation in the baking, wine, distillation, and beer making processes. These yeasts are able to inhibit undesired yeast contaminants, preventing various off-flavors and other unwanted characteristics in the finished products. Ale and lager strains that have been modified to release these toxins have reportedly retained the positive fermentation and flavor characteristics of the original strains <ref name="Bajaj_2017" />. Several strains of ''Saccharomyces eubayanus'' isolated from seeds from monkey puzzle trees in Patagonia, Argentina, were found to secrete a killer toxin that kills ''Brettanomyces'' and ''Pichia''. One strain was found to produce a lot of the toxin, which is called "SeKT". The researchers found that SeKT toxin produced by this one strain of ''S. eubaynus'' inhibited a strain of ''B. bruxellensis'' to around 50% growth after 48 hours in a wine growth medium. It also inhibited ''Pichia guilliermondii'', ''Pichia manshurica'', and ''Pichia membranifaciens'' by 50-70%. The toxin has thus been proposed as a way to limit ''Brettanomyces'' and ''Pichia'' in wine fermentations <ref>[https://www.ncbi.nlm.nih.gov/pubmed/30671692?dopt=Abstract Production of a novel killer toxin from Saccharomyces eubayanus using agro-industrial waste and its application against wine spoilage yeasts. Mazzucco MB, Ganga MA, Sangorrín MP. 2019. DOI: 10.1007/s10482-019-01231-5.]</ref>.
* [https://www.facebook.com/groups/MilkTheFunk/permalink/2202753476419521/?comment_id=2202936416401227&comment_tracking=%7B%22tn%22%3A%22R0%22%7D Bryan Heit's simple method for testing for killer sensitivity using nothing more than agar plates.]