The response of anaerobically grown Saccharomyces cerevisiae to low and high oxygen in glucose-limited chemostat cultures

Saccharomyces cerevisiae was grown anaerobically in glucose-limited chemostat culture for several generations and then exposed to either low (1.0%) or high (20.9%) concentrations of oxygen. Under these conditions the cells required approximately 2 h before starting to take up oxygen or to produce more biomass. Glycerol and ethanol concentrations, began decreasing within an hour of providing oxygen, indicating that they were no longer being produced or were being produced at a slower rate. Little glycerol consumption occurred, but ethanol consumption started after approximately 3 h in cultures receiving 20.9% oxygen. Specific glucose consumption rates decreased as biomass increased in the presence of oxygen. Although the dilution rate was maintained constant at 0.10 h-1, accumulation of biomass in the presence of oxygen indicated that the cells were growing at specific growth rates of 0.21 (1.0% O2) and 0.32 h-1 (20.9% O2) between 2 and 10 h after oxygen was provided to the cultures. Although oxygen uptake did not occur until 2 h after it was provided to the cultures, most glycolytic genes showed down-regulation within 10 minutes of its presence in the culture. Regulation of genes involved in glucose, ethanol and glycerol metabolism and respiration similarly occurred within 10 minutes of the presence of oxygen. In contrast, the concentration of most of the metabolites of central carbon metabolism did not change until more than 10 minutes exposure to oxygen.