Enhanced mutation through exposure to EMS affects the evolution of ethanol tolerance in Saccharomyces cerevisiae

Ethanol is a multifunctional compound that has many uses and can be made naturally by sugar-fermenting yeast such as Saccharomyces cerevisiae. However, ethanol is toxic to yeast, so in this study we aimed to improve yeast ethanol tolerance, which could result in greater efficiencies in the process of alcohol production. This research explores the effectiveness of artificially inducing population-level variation through the application of ethyl methanesulfonate (EMS) on increasing the ethanol tolerance in S. cerevisiae. After several rounds of selection and increasing ethanol concentrations, ranging from 9-27%, the two treatment populations (AS - Artificial Selection only; and EMS – Exposure to EMS and Artificial Selection) were compared to the initial parental population. The parental strain was tolerant to ethanol concentrations of 13%, while the AS treatment was tolerant to slightly higher levels, 16%. Both of these treatments were well below the EMS treatment which expressed a tolerance of 27%. To test differences between strains, the parental strain, selection strain, and the EMS-exposed strain were separately plated on ten 27% ethanol plates and ten 0% ethanol plates, and growth was checked after 24 hours. The EMS-exposed strain was the only strain that grew at 27% ethanol; all strains grew at 0% ethanol. These results show that EMS, artificial selection, and ethanol as a stressor might be effective in producing strains of S. cerevisiae that are able to produce greater amounts of ethanol before toxicity sets in.