Typhimurium, virulent wild type [38] clpP LT1100 C5 ΔclpP [39] clpP + LT1102 LT1100

with Tn10 linked to clpP + (linkage 48%) [39] clpP/rpoS LT1104 LT1100 rpoS::Ap [39] rpoS LT1105 C5 rpoS::Ap [39] clpP + /rpoS LT1108 LT1102 rpoS::Ap [39] csrA (sup) GMK201 C5 csrA::Kn Immunology inhibitor sup, suppressor of csrA growth defect [13] rpoS/csrA (sup) GMK206 LT1105 csrA::Kn, sup, suppressor of csrA growth defect [13] clpP/rpoS/csrA (sup) GMK207 LT1104 csrA::Kn, sup, suppressor of csrA growth defect [13] csrA + (sup) GMK209 GMK201 with plasmid pCA132 [13] Plasmids pCA132 0.7-kb csrA fragment on pFF584; Strr Spr [30] To investigate growth in broth, overnight cultures were diluted 5000-fold and incubated at 37°C with agitation. Growth was BI 10773 chemical structure measured by optical density at 600 nm (OD600). To investigate growth on solid agar at low temperature, cells were grown until OD600 0.4. Ten μl of a 10-fold dilution of the cultures were spotted on LB agar and incubated at different temperatures: 10, 15, 21, 25, 30, 37 and 42°C. Growth in LB broth at 10°C was investigated by making a 10-fold dilution of overnight culture. 40 μl of the 10−1 dilutions were inoculated in 40 ml LB broth. The culture were incubated at 10°C and at different time points, growth was measured by optical density and CFU enumeration AZD3965 nmr by spotting of 10 μl of 10-fold serial dilutions on LB agar. To estimate the

number of clpP cold suppressor mutants, serial dilutions of mutant and wild-type bacteria were plated on LB agar and incubated in parallel at 10 and 37°C. The growth parameters were estimated by the Baranyi growth equation [40] using the Excel MRIP macro DMFit (http://​www.​ifr.​ac.​uk/​safety/​dmfit). The average and

standard deviation between the biological replicates were determined in Microsoft Excel. Microscopic investigation Bacterial morphology was studied by phase contrast microscopy and by electron microscopy. Bacterial cultures for microscopy were grown as described above at low temperature. A drop of cultures were applied directly to microscope slides and observed by phase-contrast microscopy with a Zeiss Axioplan2 Microscope. For electron microscopy, bacterial cultures were grown in LB broth at 12°C. A drop of LB broth was placed onto 800-mesh copper grid, and excess liquid was removed after 10 min by filter paper. The grid was stained with 1% aqueous phosphotungstic acid (pH 7.0) for 60 s. The grid was examined with a transmission electron microscope Philips EM2085. Both for phase contrast and electron microscopy concentration by centrifugation of the clpP mutant were necessary. Western blot analysis For analysis of intracellular expression of RpoS in normally grown and cold-shocked cells, bacteria were first grown in LB broth with aeration to OD600 0.65 at 37°C. Once the cultures reached OD600 0.