Fig 1. Activation of HilD abrogates swimming motility.
(A) Cross-talk between different Salmonella regulons. Only relevant cross-regulations are shown. (B) Swimming motility in soft-agar swim plates was monitored at 37°C for 3.5 h in absence or presence of 0.2% arabinose to induce HilD production. Diameters of swimming halos were measured and normalized to the control (left and middle panels). Representative swimming halos of the analysed mutants are shown (right). Biological replicates are shown as individual data points. Horizontal bars (red) represent the calculated mean of at least eight biological replicates. Statistical significances were determined using a two-tailed Student’s t-test (***, P < 0.001; ns, P > 0.05). Strains analysed were EM808 (control), TH16339 (hilD↑), EM831 (hilDΔHTH↑) and EM930 (hilA↑). (C) Induction of SPI-1 gene expression was monitored using a PsicA-eGFP transcriptional reporter fusion. Fluorescence intensities of PsicA-eGFP fusion and single-cell swimming velocities were measured after induction of HilD production by addition of AnTc (100 ng/ml). Fluorescence intensities of the cultures were measured in a microplate reader and normalised to the measured OD600 to give relative fluorescence units (RFU). The swimming velocities were analysed via time-lapse microscopy. The plotted values represent the average of 300 or more single-cell tracks from a representative experiment. Strains analysed were EM228 (control) and EM12302 (hilD↑). hilD↑: strain expressing hilD under an inducible promoter. hilA↑: strain expressing hilA under an inducible promoter. AnTc: anhydrotetracycline.