FIG 5.

ATPase activity is reduced in the ΔrgpF mutant. (A) Cultures of S. mutans UA159, ΔrgpF, and rgpF⁺ strains were grown in continuous culture to steady state at pH values of 7 and 5. The release of inorganic phosphate was measured as a readout for membrane-bound ATPase activity. Data were normalized to activity levels for UA159 grown to steady state at pH 7 (assigned a value of 1) and are represented as mean values ± SD from three independent chemostat cultures. Statistical significance was determined by pairwise comparison using Student's t test († and ‡, P ≤ 0.05; *, P ≤ 0.02). Note the values for the ΔrgpF mutant are not statistically significant in a comparison of the activities in pH 7- and pH 5-grown cultures. (B) Transcription of atpB was determined by qRT-PCR using RNA isolated from cultures of S. mutans UA159, ΔrgpF, and rgpF⁺ strains grown in continuous culture to steady state at pH values of 7 and 5. Samples from three independent chemostat cultures were measured in triplicate and are represented as mean values ± SD. Statistical significance was determined by pairwise comparison using Student's t test († and ‡, P ≤ 0.001).