Oxygen-dependent regulation of ion fluxes and intracellular pH in Saccharomyces cerevisiae exposed to acetic acid

exchange ratios and a substantial increase in ion exchange imbalance. These effects were amplified under oxygen-limited conditions and correlated with reduced growth and metabolic activity. Moderate AA stress was accompanied by increased intracellular ATP, particularly in ATCC 9804 under oxygen limitation, whereas severe AA stress caused ATP depletion, most strongly in ATCC 13007. Notably, the more tolerant strain maintained lower intracellular proton accumulation and more efficient ion flux coordination, particularly during aerobic growth. Together, our findings demonstrate that oxygen availability fundamentally reshapes ion flux balance and intracellular pH homeostasis during AA stress. These insights have direct implications for strain selection and process optimization in industrial fermentations exposed to weak organic acid inhibition.