FIG 6.

The ΔArcD mutant's protection against acid stress is not transferable in conditioned medium. The wild type and the indicated strains were cultured for 6 days in THY medium alone (−), THY medium plus 10 mM arginine (+), or THY medium plus 50 mM arginine (++). The cultures were then filter sterilized, and the conditioned medium was used to resuspend the ΔArcB mutant to a density of ∼10⁷ CFU, which was placed back at 37°C. At the indicated time points, the cultures were resuspended, and the viability was measured as previously described. The data displayed are the mean and standard deviation of recovered CFU from at least three independent experiments. Difference in CFU were tested for significance against the wild type or between the designated strains using the Mann-Whitney U test (***, P < 0.001; ****, P < 0.0001). The level of detection (L.O.D.) was 33 CFU.