FIG. 1.

In vitro stress experiments. (A) Growth curves of the wild type (triangles) and the stkP-deficient mutant (diamonds) at different temperatures. A total of 4 × 10⁴ CFU ml⁻¹ of each strain was used to inoculate CAT medium prewarmed at the indicated temperatures. Bacteria were grown at 37°C (open symbols) and 40°C (filled symbols). Samples were taken at 1-h intervals for measurement of the OD₄₀₀. Data are representative of three independent experiments. (B) H₂O₂ survival test of the wild type (open columns) and the stkP-deficient mutant (gray columns). In the assays, cells were grown in CAT medium at 37°C to an OD₄₀₀ of 0.4 and the aliquots (10⁷ CFU) were used in each assay. Cells were incubated at 37°C for 5, 10, 15, and 20 min without or with 40 mM H₂O₂, and viable counts were carried out. Experiments were performed in triplicate. (C) Growth curves as measured by the ODs of the wild type (triangles) and the stkP-deficient mutant (diamonds) grown in CAT (open symbols) and CAT plus 400 mM NaCl (filled symbols). The growth of cultures was monitored from an initial OD₄₀₀ of 0.2. Data are representative of three independent experiments. (D) Growth curves of the wild type (triangles) and the stkP-deficient mutant (diamonds) at different pHs. Equal numbers of cells (4 × 10⁴ CFU ml⁻¹) of both the wild-type strain and the ΔstkP mutant were used to inoculate CAT medium adjusted to pHs 6.5 (filled symbols) and 7.5 (open symbols), and bacteria were grown at 37°C. Data are representative of three independent experiments. Error bars indicate standard deviations of the means.