Ethanol reduces mitochondrial membrane integrity and thereby impacts carbon metabolism of Saccharomyces cerevisiae

Saccharomyces cerevisiae is an excellent ethanol producer, but is rather sensitive to high concentration of ethanol. Here, influences of ethanol on cellular membrane integrity and carbon metabolism of S. cerevisiae were investigated to rationalize mechanism involved in ethanol toxicity. Addition of 5% (v/v) ethanol did neither significantly change the permeability of the cytoplasmic membrane of the reference strain S. cerevisiae BY4741 nor of the ethanol-tolerant strain iETS3. However, the addition of ethanol resulted in a marked decrease in the mitochondrial membrane potential and in increased concentrations of intracellular reactive oxygen species (ROS). The carbon flux was redistributed under these conditions from mainly ethanol production to the TCA cycle. This redistribution was possibly a result of increased energy demand for cell maintenance that increased from about zero to 20-40 mmol ATP (g_CDW h)^-1. This increase in maintenance energy might be explained by the ethanol-induced reduction of the proton motive force and the required removal of ROS. Thus, the stability of the mitochondrial membrane and subsequently the capacity to keep ROS levels low could be important factors to improve tolerance of S. cerevisiae against ethanol.