Effects of adhesion regulation by the ArlRS–MgrA cascade are evident in the single-cell and single-molecule analyses.

Single-cell force spectroscopy (SCFS) was used to measure the forces between single bacteria and fibrinogen (Fg) immobilized on solid surfaces (A). Box-plots show the distributions of adhesion frequencies (top) and maximum adhesion forces (bottom) for the interaction, in buffer, between single cells from the WT, ΔarlRS or ΔmgrA strains respectively and Fg surfaces (B), n = 14 (WT), 5 (ΔarlRS) or 12 (ΔmgrA). Representative retraction force curves for this experiment are shown (C). Single-molecule force spectroscopy (SMFS) was employed to map the distribution of single Fg-binding proteins on living bacteria (D). This generated adhesion force maps (scan size: 500x500 nm2; color range: 3,000 pN) recorded on WT and ΔmgrA cells, using a contact time of 100 ms or 500 ms (E). We also used SCFS to quantify the forces between single bacteria and abiotic surfaces (F). Box-plots show the distribution of adhesion frequencies (top) and maximum adhesion forces (bottom) between single bacterial cells from the WT or ΔmgrA strains and methyl-, hydroxyl- or carboxyl-terminated surfaces (G), n = 7 for each strain. Representative approach curves for the different conditions in this experiment are shown (H). Unless stated otherwise, all curves were obtained using an applied force of 250 pN, an approach and retraction speed of 1.0 μm.s-1 and a contact time of 100 ms. For all box-plots, box range = percentile 25 and 75; □ = mean; whiskers = minimum and maximum of the dataset.