Changes

Many wine yeast strains are known to be "killer" yeast strains (this term has been changed to "zymocidal" in science <ref name="Stewart_2018">[https://link.springer.com/chapter/10.1007/978-3-319-69126-8_10 "Killer (Zymocidal) Yeasts." Brewing and Distilling Yeasts. Graham G. Stewart. 2018.]</ref>). In ''Saccharomyces'', killer strains are genetically determined to secrete toxins (in the form of extracellular proteins or glycoproteins) called 'mycocins' that kill sensitive strains. These killer strains are immune to their own toxin. The mycocin toxins can act on sensitive strains in a number of ways: by blocking DNA synthesis and preventing cell division, inhibiting the synthesis of beta-glucans (β-1,6-glucan) that a part of their cell wall formation, and by causing ions to leak through the cell wall. In low dosages, which is typical in the natural environment, toxin triggers active cell death ([http://www.biology-pages.info/A/Apoptosis.html apoptosis]), while large dosages cause necrotic cell killing ([https://en.wikipedia.org/wiki/Necrosis necrosis]). One study in wine found that the use of killer strains to out compete sensitive strains resulted in off-flavors from yeast autolysis <ref>[http://www.nature.com/nrmicro/journal/v4/n3/full/nrmicro1347.html Yeast viral killer toxins: lethality and self-protection. Manfred J. Schmitt & Frank Breinig. 2006.]</ref><ref name="Hatoum2012">[http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3525881/ Rima Hatoum, Steve Labrie, and Ismail Fliss. 2012.]</ref>. Another study found that a lager strain that was genetically modified to secrete killer toxins was able to eliminate all cells of a sensitive ale strain within 24 hours of beer fermentation at a pitching rate of 99% sensitive ale strain to 1% killer lager strain, indicating that even a small amount of killer cells is enough to kill a larger population of sensitive cells <ref name="Stewart_2018" />. Neutral strains do not produce toxins, nor are they killed by them <ref>[https://books.google.com/books?hl=en&lr=&id=mvORN6OXHh4C&oi=fnd&pg=PA93&dq=Bussey,+H.+1981.+Physiology+of+killer+factor+in+yeast.+Adv.+Microb.+Physiol.+22:93-121&ots=jUY4T9NpgB&sig=aw-Y1um0KsDnGe6rRe5PTWIDYdI#v=onepage&q&f=false Advances in Microbial Physiology, Volume 22. Academic Press, Sep 15, 1981. Pg 94-95.]</ref>. Almost all ale and lager strains are sensitive to the toxins produced by killer strains <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1179271825434363/?comment_id=1179424538752425&offset=0&total_comments=5&comment_tracking=%7B%22tn%22%3A%22R%22%7D Conversation with Bryan of Sui Generis Blog on MTF on Killer Factor for Saccharomyces. 11/16/2015.]</ref><ref>[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1973.tb03515.x/pdf Strains of Yeast Lethal to Brewery Yeasts. A.P. Maule and P.D. Thomas. 1972.]</ref>.