Analysis of EvgS and its sensitivity to mild acidity in selected <i>E</i>. <i>coli</i> isolates.

<p>A: Dendrogram based on EvgS sequence alignments was constructed as described in Materials and methods. Gray shaded boxes indicate phylogenetic groups. B: Activity of the EvgA fluorescent reporter P_<i>yfdX</i><i>-yfp</i>. All of the strains carry a single copy plasmid with the EvgA reporter P_<i>yfdX</i><i>-yfp</i>_MG1655 (pMR86). The strains were cultured in minimal medium at pH 5.7 or pH 7 to OD₆₀₀ ~0.2, and fluorescence was quantified as described in Materials and methods. Values are the average fluorescence from two experiments and error bars represent the range. All of the pH 7 data bars, and the pH 5.7 data bars for some strains, are too small to be visible in the figure. C: Resistance to acid challenge. Strains were cultured in minimal medium at pH 5.7 to OD₆₀₀ ~0.2, and shocked for an hour in LB at pH 2.5 as described in Materials and methods. Percent survival values are the average of two experiments and error bars represent the range. D: Plot of fold induction of the fluorescent reporter P_<i>yfdX</i><i>-yfp</i> from panel B versus percent survival after exposure to pH 2.5, from panel C. The <i>E</i>. <i>coli</i> strains are described in detail in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007101#pgen.1007101.t001" target="_blank">Table 1</a>. Dashed lines represent the limit of detection of the assay.