Yeast mutation rates in alternative carbon sources reflect the influence of reactive oxygen species

Environmental conditions can influence mutation rates, but the reasons are often unclear. Budding yeast can utilize many carbon sources, with variation in the degree of fermentation versus respiration. Since aerobic respiration produces mutagenic reactive oxygen species, we hypothesized that yeast grown in media promoting aerobic respiration would show higher mutation rates. We found significant differences across five media types, with the highest mutation rate in pyruvate and the lowest in glucose. However, mutation rates responded to respiration rate in a nonlinear fashion, suggesting that the degree of respiration in a given environment is only partly predictive of mutation rate.