FIG 4.

Arginine and citrulline dose-dependent protection against acid stress does not directly correlate with culture pH. Wild-type bacteria and the indicated strains were cultured in THY medium supplemented with various concentrations of arginine (A and C) or citrulline (B and D) for a 6-day period. Following the 6-day period, the cultures were resuspended and an aliquot was removed and serially diluted in PBS, followed by plating on solid medium for enumeration of CFU. The cultures were then filter sterilized, and the culture pH was measured using a pH probe. The data displayed are the mean and standard deviation of recovered CFU and measured culture pH from at least three independent experiments. Differences in CFU and culture pH were tested for significance against the wild type or between the designated strains using the Mann-Whitney U test (*, P < 0.05; **, P < 0.01; ***, P < 0.001).