FIG. 3.

Maintenance of cytoplasmic pH (pHi) against decreasing extracellular pH (pHo). Strain 30-2C4 was grown in McIlvaine’s medium, harvested, and incubated at 37°C in McIlvaine’s medium at the pH values indicated. (A) Cytoplasmic pH in the absence of either lactate or ethanol. Symbols: ○, mid-exponential-phase cells, ▴, cells habituated by growth at pH 5.8; ■, cells grown into stationary phase. (B) Exponential-phase cells habituated by growth at pH 5.8 were harvested, and the cytoplasmic pH was determined at the pH indicated. Symbols: ●, no additions; ▴, lactate (50 mM); ■, ethanol (5%). Standard deviations varied from 0.02 to 0.25 but were routinely less than 0.06.