We are upon the hour of a new year, which of course means booze! Now, we all know that there will be a medley of alcohols consumed tonight. I am sure that we are also all fully aware that we owe thanks to yeasts, for making that fermentation process so readily available.
But not all yeasts want to help with your intoxication. And in the same way they will spoil your good times, those yeasts are called spoilage yeasts.
One of the widest spread spoilage yeasts, Zygosaccharomyces bailii, is so successful because it has the ability to tolerate a wide range of stressful living conditions (like fermented products.) While many products like wine, mayonnaise, and even pickles, are generally described to be shelf stable; Z. bailii is ready to get all up in there and have a good time. One of the sweet skills that lead this yeast to be successful is that it can metabolize both glucose, and acetic acid (which is generally seen as a stressor/killer of yeasts.)
|Zygosaccharomyces bailii wants to ruin your Snakejuice|
The Fate of Acetic Acid during Glucose Co-Metabolism by the Spoilage Yeast Zygosaccharomyces bailii
In order to determine whether Z. bailii grew more efficiently in the presence of just one substrate or the other, the team grew strains in isolated substrates as well as mixed substrates of Acetic Acid and glucose. Throughout the growth cycle they measured the biomass and compared amongst the cultures. The results of this demonstrated a number of things.
When comparing those growth rates and biomass produced on the isolated substrates to those on the mixed substrate cultures, the team found that a mixed growth medium held a lower growth rate at a pH of 3.0 over either pure substrate. This suggests that with the pH lowered the acetic acid affects efficiency, which is evidence of a need by the cell, to overcome intracellular acidification. This is reinforced by the observation that when grown at a higher pH of 5.0 the decrease isn't evident. A similar difference in growth rate is noticed in the purely acetic acid substrate cultures. However; when grown on a mixed substrate of Glucose and acetic acid, Zygosacharomyces bailii utilizes both the acid and sugar simultaneously. The yeast appears to use each of the substrates individually as both a carbon source and an energy source, showing no effect in the presence of the other. This is significant, because generally speaking the presence of glucose reduces the usage of substandard (energy wise) carbon and energy sources.
By using magnetic resonance spectroscopy and measuring 14C at various pathway steps, the researchers were able to determine that even when glucose is present, acetic acid will act as an additional source of acetyl-CoA during the Krebs Cycle, as well as for lipid biosynthesis. Basically that means Z. Bailii takes a typical environmental stressor and uses it to make extra amounts of the precursors for fueling one of the major energy cycles. And thus, your drink and New Year's Eve Bash are destroyed.
Rodrigues, F., Sousa, M., Ludovico, P., Santos, H., Côrte-Real, M., & Leão, C. (2012). The Fate of Acetic Acid during Glucose Co-Metabolism by the Spoilage Yeast Zygosaccharomyces bailii PLoS ONE, 7 (12) DOI: 10.1371/journal.pone.0052402
DTDT (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Gif - Ron Swanson of Parks and Recreation via GIFSoup