Three-dimensional aggregates formed by bacteria linked to each other can be seen in MB, leaving large bacteria-free areas. Conversely, in Figure 4B, the substrate appears to FHPI in vivo be covered by a near continuous and homogenous layer of bacteria and EPS. In this case, three-dimensional aggregates are present in a remarkably lower degree. These results revealed a different interaction between the substrate and the bacterial envelope in function of the culture medium. Thus, in MH2, bacteria-substrate

interaction is clearly favoured in comparison to MB. Figure 4 Representative cross-section of 2D peak force tapping 50 x 50 μm 2 images. (A) and (B), topographic images of MB and MH2, respectively, in brown; (C) and (D), Young’s modulus quantitative, in gold; (E) and (F), adhesion forces, grey. On the other hand, Figures 4C-D compare the Young’s modulus and Figures 2E-F the adhesion force quantitative mappings of the same surface area for MB and MH2. In this context, it should be taken into account that the greater the brightness of the patches the larger corresponding values of the magnitudes analysed. In general terms, images show that the higher values in Young’s modulus and adhesion force correspond to the bacteria-free

substrate areas. Note that the higher pikes present in the cross sections (E > 0.7 MPa) are related to contributions due to bacteria/EPS-free substrate. Thus, Young’s modulus Mocetinostat cell line exhibited by bacteria resulted to be significantly larger for those grown in MH2 (Additional file 4: Table buy AZD5363 S3). However, regarding adhesion forces, the situation was exactly the opposite with the higher figures corresponding

to MB. In addition, by considering the average size of certain Young’s modulus spots, especially those associated with clusters of bacteria present in the topographic image, it can be concluded that these groups of bacteria seem to be surrounded by EPS which spreads to the cell-substrate interface (see also Additional file 6: Figure S3A-F). Table 3 shows the averaged values of Young’s modulus and adhesion forces recorded for individual bacterial cells grown in the four different media. Our overall experimental data (see histograms in Additional file Sclareol 8: Figure S5) confirmed the trend previously described a clear correlation between the rising in Young’s modulus and the diminishing in the adhesion response is exhibited when modifying the growth medium. As shown in Table 3, values registered for MH2 almost doubled those grabbed for MB. Anyway, the biofilm developed in MH2 showed the highest elasticity values registered. It should be noted that these results obtained for the elasticity properties of the external covering layer of S. algae cells are in the same order of magnitude as those reported for other gram-negative bacteria [59, 60].