Changes

Not only do <nowiki>[</nowiki>GAR⁺<nowiki>]</nowiki> yeast have the ability to ferment other sugars at the same time as glucose, but it has been proposed by some researchers that they produce less alcohol (for example in the referenced study, the <nowiki>[</nowiki>gar^-<nowiki>]</nowiki> ''Saccharomyces'' cells fermented grape must into a 12% ABV wine, and the <nowiki>[</nowiki>GAR⁺<nowiki>]</nowiki> ''Saccharomyces'' cells fermented the same wine must into an 8% ABV wine <ref name="cross-kingdom"/>). Viability over time is also increased in yeast cells that are <nowiki>[</nowiki>GAR⁺<nowiki>]</nowiki> versus those that aren't. In wild fermentation of grapes, the wild <nowiki>[</nowiki>GAR⁺<nowiki>]</nowiki> ''S. cerevisiae'' strains thrived over the other types of fungi that were found on the wild grapes. While the induction of <nowiki>[</nowiki>GAR⁺<nowiki>]</nowiki> can occur in yeast without the presence of lactic acid, the presence of lactic acid greatly increases the occurrence of <nowiki>[</nowiki>GAR⁺<nowiki>]</nowiki> in yeast cells, with higher concentrations of lactic acid producing more occurrences of <nowiki>[</nowiki>GAR⁺<nowiki>]</nowiki> cells. The lactic acid merely has to be present for this to happen, and the yeast's ability to metabolize lactic acid or not does not have an effect. It is thought that this benefits both the <nowiki>[</nowiki>GAR⁺<nowiki>]</nowiki> ''S. cerevisiae'' and the lactic acid bacteria, which are often found together in the wild during fermentation of fruit. The bacteria isn't killed by higher alcohol levels, and the yeast has a broader food source. This effect that lactic acid bacteria have on yeast is known as ''cross kingdom chemical communication'' <ref name="cross-kingdom" /><ref name="Garcia_2016" />. Ramakrishnan et al. (2016) disputed this claim by showing that <nowiki>[</nowiki>GAR⁺<nowiki>]</nowiki> yeast can still ferment sugars adequately, and showed that these yeast were slower at depleting nitrogen and oxygen, thus leaving these resources for the bacteria and creating an environment that stresses the yeast which results in the reported stuck wine fermentations<ref name="Ramakrishnan_2016" />.

In a previous study by Jarosz et al. (2014), it was observed that only certain bacteria species had the effect of inducing <nowiki>[</nowiki>GAR⁺<nowiki>]</nowiki> in some strains of yeast. These bacteria included ''P. damnosus'', ''Lactobacillus kunkeei'', and species from genres ''Staphylococcus'', ''Micrococcus'', ''Bacillus'', ''Listeria'', ''Paenibacillus'', ''Gluconobacter'', ''Sinorhizobium'', ''Escherichia'', ''Serriatia''. In this study, ''L. brevis'', ''L. hilgardii'', ''L. plantarum'' did not appear to induce <nowiki>[</nowiki>GAR⁺<nowiki>]</nowiki> in yeast <ref name="cross-kingdom" />. At the time of this study, it was not understood that lactic acid was an inducer of <nowiki>[</nowiki>GAR⁺<nowiki>]</nowiki>. Additionally, the method they used to discover this was simply to streak bacteria next to yeast on a plate, and see if it grew on a medium that would show whether or not they bypassed glucose repression. Therefore, it is possible that not enough lactic acid was produced, or that they didn't give the bacteria enough time to have an effect on the yeast. More work would need to be done to show that indeed all lactic acid bacteria that produce lactic acid have this effect on yeast, and also it is not clear whether other bacterial metabolites may influence this phenomenon <ref name="preiss">[https://www.facebook.com/groups/MilkTheFunk/permalink/1500240613337481/ Conversation with Richard Preiss on MTF. 12/7/2016.]</ref>. Ramakrishnan et al. (2016) more recently confirmed that the induction of <nowiki>[</nowiki>GAR⁺<nowiki>]</nowiki> is not only species dependent, but strain dependent within species <ref name="Ramakrishnan_2016"/>.