dynamics during growth. (a) Growth (filled triangles) and pHc (filled circles) were monitored during growth on glucose in microplates. Data points represent the average of 24 biological replicates, error bars represent standard deviations. (b) Medium exchange experiments show that the pHc decrease during the growth phase is determined not by the state of the cell, but the environmental conditions generated in the culture medium. Early and late log phase cells were harvested and resuspended in fresh medium, late log medium, and late log medium supplemented with all nutrients. (c) CO2 causes pHc acidification. Strains were grown for 10 hours in either aerobically (closed bars) or anaerobically (open bars). After 10 hours the pHc of both strains was determined. Cultures were subsequently aerated for 30 minutes by bubbling air through the culture followed by pHc determination.