Figure 2.

emrKY expression in S. flexneri is modulated by specific stimuli both outside and inside U937. (A) Expression of emrKY in response to the indicated stimuli in strain M90T pZemrK-gfp grown in LB or M9 complete medium. (B) Expression of emrKY in response to different pH values (from pH 5.6 to 7.4) in M9 complete medium supplemented with 0.1 M KCl. (C) Expression of emrKY in response to increasing concentration of KCl, NaCl, MgCl₂ or sucrose added to M9 complete medium at pH 6. The addition of 0.05 M MgCl₂ or 0.1 M sucrose (not shown) has the same effect as 0.1 M MgCl₂ or 0.2 M sucrose, respectively. In A,B and C the expression of emrKY was measured as a function of GFP production in M90T pZermK-gfp strain. (D) Intracellular pH values (filled symbols) of mock (square) and M90T infected U937 cells (circle) at 3 hours p.i. pH was measured by loading cells with green pHrodo dye and quantified on the relative standard curves obtained with four different calibrated pH buffers. Fluorescence intensity was read on the Victor multilabel counter (Perkin Elmers). (E) Expression of mdtJI in response to the indicated stimuli measured as a function of GFP production in M90T pZmdtJ-gfp strain grown in M9 complete medium. GFP production was evaluated by reading fluorescence intensity on Infinite 200 (TECAN) every 15 minutes throughout 3 hours. GFP values were normalized to the bacterial cell concentration and the results shown are the mean of three independent experiments. Three independent experiments were carried out and statistical significance was determined by a one-tailed ANOVA, and p values are as follows: *p < 0.05. Error bars represent SD.