P2: Understanding the effects of aromatic alcohols on the growth of Saccharomyces cerevisiae

Ethanolic fermentations such as biofuel, spirits, beer and wine are prone to contamination with lactic acid bacteria (LAB). These contaminations often cause stuck fermentations resulting in costly loss of product. The primary goal of this research is to gain a better understanding of the chemical interactions taking place between Saccharomyces cerevisiae and LAB. Research has shown that the production of lactic acid alone is not a significant cause of decreased ethanol production. Given the known sensitivity of yeast to certain quorum sensing compounds, we propose that other compounds may play a role in signaling that result in decreased growth and loss of ethanol. LAB are known to produce aromatic alcohols through the Ehrlich Pathway. We have examined the effects on yeast growth and fermentation of three of these compounds: 2-Phenolethanol, Tyrosol, and Tryptophol. Plate reader data indicates that 2-Phenolethanol, Tyrosol and Tryptophol inhibit cell growth. In addition, a continuous feed fermentation was performed using Saccharomyces cerevisiae strain BY4741and media with 1nM 2-Phenolethanol. In this fermentation, temperature, pH and agitation were controlled and growth was monitored using OD, hemacytometer and plate count. HPLC was conducted to monitor glucose, ethanol and 2-Phenolethanol levels. This fermentation demonstrated a 25% decrease in ethanol production and cell growth over a 24hr period.