FIG 4.

1457 ΔADI has a reduced ability to maintain an neutral intracellular pH in an acidic extracellular environment. Strain 1457 or 1457 ΔADI was grown in TSB supplemented with 35 mM glucose and 5 mM arginine. After 24 h, aliquots were removed, washed, and labeled with CFDase for measurement of intracellular pH. Labeled cells were incubated in McIlvaine's sodium citrate buffer at pH 5, 6, and 7, and the fluorescence was measured for determination of intracellular pH. Data were analyzed using the Student t test (n = 3; **, significant difference from strain 1457 with P < 0.05).