Bacterial strains, media, and chemicals

All strains are listed in S1 Table. Escherichia coli strains DH5α and BTH101 were used for cloning procedures and bacterial 2-hybrid assay, respectively. E. coli cells were grown in Lysogeny Broth, at 37°C or 28°C. For BACTH experiments, gene expression was induced by the addition of iso-propyl-β-D-thio-galactopyranoside (IPTG, Sigma-Aldrich, St. Louis, MI, USA, 0.5 mM), and plates were supplemented with 5-bromo-4-chloro-3-indolyl-β-D-galactopyranoside (X-Gal, Eurobio, Les Ullis, France, 40 μg.mL⁻¹). F. johnsoniae CJ1827, a streptomycin-resistant rpsL2 derivative of ATCC 17061 (UW101), was used as model micro-organism. F. johnsoniae cells were grown at 28°C in Casitone Yeast Extract (CYE) medium [69] or Motility Medium (MM) [70] as indicated. For selection and maintenance of the antibiotic resistance, antibiotics were added to the media at the following concentrations: erythromycin, 100 μg.mL⁻¹; streptomycin, 100 μg.mL⁻¹; tetracycline, 20 μg.mL⁻¹, ampicillin, 100 μg.mL⁻¹, kanamycin, 50 μg.mL⁻¹, and chloramphenicol, 40 μg.mL⁻¹. Specific enzyme and chemicals source were as follows: trypsin (Sigma-Aldrich), CCCP (Sigma-Aldrich, 10 μM), nigericin (Nig, Sigma-Aldrich, 7 μM), valinomycine (Val, Sigma-Aldrich, 40 μM), sodium azide (Az, Sigma-Aldrich, 1.5 mM), arsenate (Ars, Sigma-Aldrich, 20 mM), and DCCD (Sigma-Aldrich, 100 μM).