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updated glucose repression definition
===Genetic Manipulation===
It has recently been discovered that both L-lactic acid and D-lactic acid produced by lactic acid bacteria can manipulate a genetic trait in yeast that dictates how yeast ferments different types of sugars, including some strains (but not all) of ''Saccharomyces cerevisiae'' and ''Brettanomyces bruxellensis'' <ref name="Garcia_2016">[https://elifesciences.org/content/5/e17978 A common bacterial metabolite elicits prion-based bypass of glucose repression. David M Garcia, David Dietrich, Jon Clardy, Daniel F Jarosz. 2016.]</ref>. Normally ''Saccharomyces'' and many other types of yeast will preferentially metabolize glucose when glucose is present and they ignore other sugars such as maltose and maltotriose until the glucose is completely consumed(or until 40-50% of glucose is consumed in the case of wort and in anaerobic conditions <ref>Stewart, G. G. (2006). Studies on the uptake and metabolism of wort sugars during brewing fermentations. Tech. Q. Master Brew. Assoc. Am. 43:265-269. </ref>). This is called "glucose repression". Recently it has been identified that lactic acid produced by lactic acid bacteria in the presence of some yeast strains turns off this "glucose repression" in yeast, allowing them to simultaneously ferment all types of sugars. This has a side effect of limiting attenuation in wine, and has been one of the identified causes of stuck wine fermentations (it has been observed as far back as Louis Pasteur that stuck wine fermentations often contain lactic acid bacteria) <ref name="cross-kingdom">[http://weitzlab.seas.harvard.edu/files/weitzlab/files/2014_cell_jarosz.pdf Cross-Kingdom Chemical Communication Drives a Heritable, Mutually Beneficial Prion-Based Transformation of Metabolism. 2014. Daniel F. Jarosz, Jessica C.S. Brown, Gordon A. Walker, Manoshi S. Datta, W. Lloyd Ung, Alex K. Lancaster, Assaf Rotem, Amelia Chang, Gregory A. Newby,David A. Weitz, Linda F. Bisson, and Susan Lindquist. Cell. 2014 Aug 28;158(5):1083-93.]</ref>.
The ability for yeast to bypass glucose repression and ferment multiple types of sugars simultaneously is controlled a by a protein-based genetic [https://en.wikipedia.org/wiki/Prion prion] called '''<nowiki>[</nowiki>GAR<sup>+</sup><nowiki>]</nowiki>'''. These genetic "prions" are not the same as DNA in genes, but are rather misfolded proteins contained in the cytoplasm of the cell. These proteins are dominant over <nowiki>[</nowiki>gar<sup>-</sup><nowiki>]</nowiki>, and are passed to the offspring of the cell during cell division. This type of passing of genetic material from mother cell to daughter cell is much more frequent than genetic mutations, and probably exists to help yeast populations quickly adapt to rapidly changing conditions in their environment. Normally in brewers yeast only a small number of cells are <nowiki>[</nowiki>GAR<sup>+</sup><nowiki>]</nowiki> if any at all. In the brewing environment where there is no competition from other yeasts, brewers yeast benefits from consuming glucose first. In the wild, however, many more strains have been found to be <nowiki>[</nowiki>GAR<sup>+</sup><nowiki>]</nowiki>. This is thought to be an adaptive advantage for wild yeast depending on the environments in which they live; such yeasts can "hedge their bets" towards consuming other types of sugars, with the side effect of allowing bacteria to produce compounds such as lactic acid that may inhibit competing yeasts <ref name="Jarosz_2014">[http://www.cell.com/cell/abstract/S0092-8674(14)00974-X An Evolutionarily Conserved Prion-like Element Converts Wild Fungi from Metabolic Specialists to Generalists. Daniel F. Jarosz, Alex K. Lancaster, Jessica C.S. Brown, Susan Lindquist. Cell. Volume 158, Issue 5, p1072–1082, 28 August 2014]</ref><ref name="cross-kingdom">[http://weitzlab.seas.harvard.edu/files/weitzlab/files/2014_cell_jarosz.pdf Cross-Kingdom Chemical Communication Drives a Heritable, Mutually Beneficial Prion-Based Transformation of Metabolism. 2014. Daniel F. Jarosz, Jessica C.S. Brown, Gordon A. Walker, Manoshi S. Datta, W. Lloyd Ung, Alex K. Lancaster, Assaf Rotem, Amelia Chang, Gregory A. Newby,David A. Weitz, Linda F. Bisson, and Susan Lindquist. Cell. 2014 Aug 28;158(5):1083-93.]</ref>.