Figure 1.
AFM height and stiffness data for Rhodococcus wratislaviensis.
AFM height (a–b) and stiffness (e) images of Rhodococcus wratislaviensis in their physiological (MM) medium. Height (c–d) and stiffness (f–g) profiles along dashed lines in figures (a) or (e), respectively, are plotted.
Figure 2.
AFM approach curves in MM liquid are plotted for the glass substrate (black line), the Rhodococcus wratislaviensis bacterium (red line) and its slime (blue line). The raw curves have been shifted along X axis to better view the contrast in slopes at the force setpoint. The dashed lines are an illustration of how the effective stiffnesses are calculated from these approach curves (best linear fit for a length window of 10 nm).
Figure 3.
Stiffness histogram for Rhodococcus wratislaviensis.
Stiffness histogram related to AFM stiffness image (figure 1.e) is shown.
Figure 4.
AFM height and stiffness data for Rhodococcus wratislaviensis.
AFM height (a–b) and stiffness (c) images of Rhodococcus wratislaviensis in MM medium are shown. These images are taken at zone delimited by the white square in figure 1. Stiffness histogram related to AFM stiffness image (figure 4.c) is shown in figure 4.d.
Figure 5.
Optical snapshots of the gliding Nostoc.
Optical snapshots of the gliding of Nostoc bacterium upon the glass slide are shown. The scale is given by the black line (10 microns). The bacterium is moving from the right to the left of the images as indicated by the displacement of the landmark (arrow) between the two images (Δt = 12s).
Figure 6.
Nostoc displacement and speed curves as measured by optical microscopy.
Figures 6.a–b: The displacement, along the X axis (see figure 5), of a Nostoc bacterium, as determined by optical microscopy, is plotted (full line) versus time during its gliding movement on the surface of the glass slide. The AFM cantilever is 500 nm far from the substrate.Figure 6.b: The displacement along the X axis of another Nostoc bacterium, as determined by optical microscopy, is plotted (full line) versus time. These data are related to the sequence labeled “number 1” in the main text. The AFM tip is now in contact with the substrate and scans it. The AFM fast scan direction is along X. The movement of the AFM cantilever along Y (slow axis) is plotted versus time (black triangles; the line is a guide for the eye): every triangle corresponds to a measured position (one optical image every 4 seconds). The starting times of the successive AFM images are marked by the short vertical segments. The indexation number of the AFM images is labeled in the squared box. The successive X positions of the bacterium as determined from AFM images (see figure 7) are marked by the stars (*), the dashed line being a guide for the eye. The scanning time for a full AFM image is 35 seconds. In figure 6-c (upper curve with left triangles) gliding speed along X axis of Nostoc as calculated from to displacement data in figure 6.b is plotted versus time.
Figure 7.
AFM height images of Nostoc (sequence #1).
Successive AFM height (1–5) images of Nostoc cyanobacterium in its physiological medium are plotted. Time interval between two consecutive images is equal to 35 seconds. For comparison, an optical image acquired during this AFM sequence was numerically treated to get the same magnification as in AFM images (1–5).
Figure 8.
AFM height and stiffness data for Nostoc (sequence #1).
AFM stiffness (a) and height (b) images of Nostoc in its physiological (BG11) medium are shown. They correspond to image 7.5. Stiffness (c) and height (e) profiles along the black dash/dot line in figures (a) or (b) are plotted. Stiffness (d) and height (f) profiles along the red dashed line in figures (a) or (b) are plotted. The blue circles in figures 8.e and 8.f were drawn to point out the presence of ECM at the edges of the Nostoc profile.
Figure 9.
AFM height and stiffness data for Nostoc (sequence #1).
AFM height (a, c) and stiffness (b, d) images of Nostoc in BG11 medium are shown. They correspond to image 7.3. In images (b) and (d), the contrasts were increased to show the presence of the slime layer. Height (e) and stiffness (g) profiles along the black dash/dot line in figures (a–d) are plotted. Height (f) and stiffness (h) profiles along the red dashed line in figures (a–d) are plotted. Stiffness histogram related to the whole stiffness image (figure 9.b or 9.d) is shown in figure (i). In figure (j), the histogram was calculated to the only portion of image 9.b (or 9.d) at the left side of the dotted line. The peaks resulting from the deconvolution of this histogram are plotted with colored lines.
Figure 10.
AFM height images of the gliding Nostoc (sequence #2).
- Figure 10.a–c: Three AFM height images of the gliding Nostoc bacterium upon the glass slide. In figure 10.c. the bacteria glided away from the AFM scan zone. A common color scale for height was applied for all these images except for the lower part (below the thick white line) of picture (d) where height contrast was enhanced. - Figure 10.d: Visualization of the vertical gliding movement of the Nostoc. It is done by the superposition of the image of the bacteria as determined in figure 10.b (bacterium at the right side of image 10.d) with that measured at t1, 79 s earlier (figure 10.a) and vertically shifted along the white arrow (shift length: 19.3±0.2 microns). For reasons of clarity a lateral shift between the native figures 10.a and 10.b was applied.
Figure 11.
AFM height and stiffness profiles for Nostoc (sequence #2).
AFM height (_0, _1) and stiffness (_2) profiles for Nostoc bacterium (b_) along red line in images 10.b and 12.b and for the excreted slime (s_) along blue line in images 10.c and 12.c are plotted. Height profiles in figures _b0 and _s0 are displayed with the same height scale. Idem for those in figures _b1 and _s1 but with an enhanced contrast.
Figure 12.
AFM stiffness data of the gliding Nostoc (sequence #2).
Nostoc AFM stiffness images are shown. They correspond to the three equivalent height images in figure 10.a–c. A common grey scale for stiffness was applied for the upper part (above the wide black line) of these images. At the lower parts stiffness contrast was enhanced. In figure 12.d stiffness histograms for Nostoc bacterium (solid line) and slime (crosses) are shown.
Figure 13.
AFM stiffness and height data for Nostoc (sequence #3).
a; b: two successive AFM stiffness images of Nostoc are shown. Height (c) and stiffness (d) profiles along the black full line in image (a) and the black dashed line in image (b) are plotted with full and dashed lines respectively. Height (e) and stiffness (f) profiles along the red full line in image (a) and the red dashed line in image (b) are plotted with full and dashed lines respectively. Stiffness histograms related to AFM stiffness data from figure a (full line) and figure b (dots and dashed line) are shown in figure (g).
Table 1.
Values of effective stiffness and cellular spring constant (in italics) for the two studied bacteria and their different components.
Figure 14.
Variation of the slime thickness with the Nostoc gliding speed.
Table 2.
Turgor pressure for the studied bacteria at different gliding speeds.
Figure 15.
AFM approach and indentation curves for Nostoc and Rhodococcus wratislaviensis bacteria, ECMs and slimes.
Typical curves of force versus vertical piezo displacement (a_) and force versus indentation (b_) for Nostoc bacterium (_1), slime (_2), ECM (_3) and for R. wratislaviensis bacterium (_4), slime (_5) are plotted. Solid lines in figures (b_) are the best fits by applying Hertz model (see main text for details).
Table 3.
Young modulus for the studied bacteria at different gliding speeds.