Fig. 3: Identification of a morphological developmental transition at the tip of mouse-SFB.

a−e Morphological stages identified at the tip of mouse-SFB. a/c/d/e(i), Representative tomographic slices from reconstructed tomograms showing SFB tip of stages: 1 (EMD-52685, Supplementary movie 5), 3 (EMD-52676, Supplementary movie 6), 4 (EMD-52677, Supplementary movie 7) and 5 (EMD-52678, Supplementary movie 8). b(i) Representative projection image of stage 2. SFB selected as representative of Stages 1–5 are 2.2, 2.3, 3.1, 12.0, and 15.6 µm in length, respectively. a–e(ii), Segmentation rendering of mouse-SFB tip from stages 1–5. The color legend is displayed at the bottom of the figure. The coloring of the hair-like structures (HLS) denotes their qualitative appearance. a−e(iii), close-ups of the mouse-SFB tip from stages 1–5. a−e(iv), Schematic representation of the mouse-SFB tip from stages 1–5. f Pie chart showing the percentage of IOs below 3.2 µm in length identified in each tip stage shown in (a−d). IOs for which the tip stage could not be identified (UD: unidentified) and for which the distinction between tip stage 4 and 5 could not be made are also shown. Close-ups of side of the mouse-SFB tip from: g(i) stage 3, h stage 4 and i(i) stage 5. g/i(ii) schematic representation of the layers present at the side of the mouse-SFB tip assigned to: g(ii) stage 3 and i(ii) stage 5. Representative tomographic slices of the distal end of a mouse-SFB IO in which a hair-like layer (HLL) was j absent (EMD-52696) and k present (EMD-52679). The length of the selected IOs was 2.4 and 2.3 µm, respectively. DisHLS disordered hair-like structures; HLL hair-like layer; SL surface layer (S-layer); OW outer wall zone; IW inner wall zone; M membrane; C cytoplasm. l/m, Length of: l mouse-SFB (mSFB) IOs (n = 44) and m total mouse-SFB (n = 60) assigned to each stage and obtained from 7 independent experiments. A dashed line separates small (<3.2 µm) and outgrowing IOs (>3.2 µm) (l). n Length of hair-like structures (HLS) from the tip of SFB assigned to stages 3–5. Hair-like structures length was measured from tomograms of 5 bacteria per stage from 2 independent experiments. For each bacterium, 10 structures were measured from 5 tomographic slices (n = 250 measurements). For l–n individual measurements and the corresponding mean are shown. The statistical significance was assessed using a Kruskal–Wallis test followed by a Dunn’s test correction for multiple comparisons (l: stage 1 vs. 5, p = 0.0158; stage 2 vs. 5, p = 0.0160; stage 3 vs. 5, p = 0.0288; m: stage 1 vs. 4, p = 0.0010; stage 2 vs. 4, p = 0.0016; stage 3 vs. 4, p = 0.0040; stage 1 vs. 5, p < 0.0001; stage 2 vs. 5, p = 0.0002; stage 3 vs. 5, p = 0.0005; n: p < 0.0001). Source data are provided as a Source Data file for (f, l–n). Scale bars: a–e(i, ii): 50 nm; a–e(iii), g–i, j, k: 20 nm.