Fig 5.

Activity of the PhoP-PhoQ system in nonproliferating intracellular S. Typhimurium responds to intravacuolar acidic pH. (A) Effect of the dissipation of intravacuolar acidification on the induction of the PhoP-PhoQ system. Shown are the relative levels of the 3× FLAG-tagged proteins MgtC and PagC produced by intracellular bacteria isolated from NRK-49F fibroblasts that were left untreated or were treated with 100 nM bafilomycin (BAF), an inhibitor of vacuolar acidification. OmpA (bacterial protein) and calnexin (eukaryotic protein) were used for loading controls. (B) Effect of loss of vacuolar acidification on the viability of intracellular bacteria. Shown are the ratios of viable intracellular bacteria enumerated at 24 h versus 2 h. Data are the means and standard deviations from three independent experiments. **, P = 0.001 to 0.01; ***, P < 0.001; n.s., not significant by a Student t test.