Changes

Many wine yeast strains are known to be "killer" yeast strains. In ''Saccharomyces'', killer strains produce toxins called 'mycocins' that kill sensitive strains. 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 the cell wall component called "β-1,3-glucan", and by causing ions to leak through the cell wall. One study in wine found that the use of killer strains to out compete sensitive strains resulted in off-flavors from yeast autolysis <ref name="Hatoum2012">[http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3525881/ Rima Hatoum, Steve Labrie, and Ismail Fliss. 2012.]</ref>. 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>. In ''Saccharomyces'', four toxins have been identified: K1, K2, K28, and Klus, the first three of which can only kill other strains/species of ''Saccharomyces''. The Klus toxin has been found to kill yeast from other genra, such as ''Hanseniaspora spp.'', ''Kluyveromyces lactis'', ''Candida albicans'', ''Candida dubliniensis'', ''Candida kefir'' and ''Candida tropicalis'', and the K1, K2 and K28 killer strains of ''S. cerevisiae'' <ref name="Rodriguez">[http://aem.asm.org/content/77/5/1822.long A New Wine Saccharomyces cerevisiae Killer Toxin (Klus), Encoded by a Double-Stranded RNA Virus, with Broad Antifungal Activity Is Evolutionarily Related to a Chromosomal Host Gene. Nieves Rodríguez-Cousiño, Matilde Maqueda, Jesús Ambrona, Emiliano Zamora, Rosa Esteban and Manuel Ramírez. 2011]</ref>. However, none of the toxins secreted by killer strains of ''Saccharomyces'' have been found to kill ''Brettanomyces'' <ref>[http://www.scielo.org.za/scielo.php?pid=S2224-79042015000100010&script=sci_arttext&tlng=pt Non-Saccharomyces killer toxins: Possible biocontrol agents against Brettanomyces in wine? S. Afr. J. Enol. Vitic. vol.36 n.1 Stellenbosch. 2015.]</ref>. The K1 toxin is most active between a pH of 4.6 and 4.8, while K2 and Klus are active around a pH of 4.0 to 4.3 <ref name="Rodriguez"></ref>.  Strains of the yeast species ''Wickerhamomyces anomalus'' and ''Kluyveromyces wickeramii'' have been found to inhibit ''Brettanomyces''. 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>.