FIG 4.

Proton permeability is disrupted in the ΔrgpF mutant. Cultures of S. mutans UA159, ΔrgpF, and rgpF⁺ strains were grown in continuous culture to steady state at pH values of 7 and 5. At the 50-min time point, butanol was added to samples (10% [vol/vol] final concentration) to lyse cells. Terminal pH values listed represent mean pH recordings (±SD) at the 80-min time point, where the pH of the ΔrgpF mutant was significantly lower (†, P ≤ 0.02) than that of both UA159 and the rgpF⁺ complement under the same conditions. The terminal pH values for the ΔrgpF mutant strain were also significantly different between pH 7 and pH 5 (‡, P ≤ 0.02). Data were derived from three independent chemostat cultures, each performed in duplicate and represented as the mean values ± SD. Statistical significance was determined by a pairwise comparison using Student's t test.