Quantification of the transient and long-term response of Saccharomyces cerevisiae to carbon dioxide stresses of various intensities

Carbon dioxide (CO2) is a major compound of microbial metabolism both as a substrate and as a product but high dissolved carbon dioxide concentrations have long been known to affect yeast physiology. This work investigates the energetic aspects of the transient and long-term responses of yeast chemostat cultures submitted to different step-increases of the dissolved CO2 concentrations. It was demonstrated that a CO2 shift-up triggered a transient metabolic response characterized by an increase of the specific respiration rate (up to +37%), the mobilization of storage sugars, excretion of ethanol and acetate (up to 50 mg L-1) and by the uptake of potassium (+30 mM) and magnesium (+20 mM) ions. The energy generation by the yeast metabolism temporarily increased and a transient decrease in the biomass synthesis was observed. This short-term response was not dependent of the amplitude of the shift-up and could not be explained by pH homeostasis only. Moreover, on the long-run CO2 created an energy drain that was proportional to its concentration as the limp value decreased from 12.7 gx mole(ATP)(-1) to 9.57 gx mole(ATP)(-1) when the dissolved CO2 concentiation was increased from 1.4 mM to 17.09 mM. Succinate excretion was also observed for CO2 enriched cultures and its production rate was found proportional with increasing CO2 concentrations. Finally, we pointed out that yeast cells may adapt to high CO2 concentrations in the long-run. This work illustrates the regulation of physiologic and metabolic homeostasis of yeast cells when facing CO2 stress