putrefaciens cells depending on the culture conditions and on the pH, respectively [61, 62]. Average adhesion forces are shown in Table 3. As discussed before, an opposite correlation among data for Young’s modulii is observed. Thus, figures obtained for MH2 were significantly lower than those obtained for MB (Additional file 4: Table S3). Regarding this point, it should be noted that whereas Young’s C188-9 modulus

is directly dependent on the mechanical behaviour of the outer part of the bacteria under tip indentation, adhesion forces imply specific attractive interactions with the tip. In this sense, it is worth noting that the abovementioned correlation has not necessarily to be like that. Although AFM tips have not been functionalised and consequently the adhesion force response recorded is due to non-specific interactions [63], it should be noted that AFM tips, bacteria and incubation times remained unchanged in all the experiences carried out. Therefore, differences observed for the biofilms grown in the different media reflect unambiguously a significant impact on the physicochemical properties of biofilms. Consequently, these results allow us to conclude the substantial

effect of modifying the culture medium on the nanomechanical 17DMAG and physicochemical behaviour exhibited by the resulting biofilms. AFM force-distance curve analysis has also been carried out in order to assess kB, the spring constant of the bacteria, which eventually resulted also dependent on the growth medium. Thus, Figure 5A shows representative force-distance curves registered in seawater for a stiff surface, mica (black line), and for representative single deformable bacteria grown in MB (red) and in MH2 (dark green). In this context, considering the relevant differences exhibited by the indentation depths grabbed for MB and MH2, a differential elasticity response can be easily concluded. Indeed,

envelope belonging to bacteria grown in MH2 selleck kinase inhibitor showed noticeable more rigid profiles than those corresponding to MB (Figures 5B-C). Figure 5 Representative force-distance curves. (A) Representative NADPH-cytochrome-c2 reductase force-piezo displacement measured on mica (black) and on top of single bacteria grown in MH2 (dark green) and in MB (red), obtained in seawater. Loading force-indentation depth (blue) curves resulted from subtracting black curve from the green (B) and the red ones (C) at constant loading force. Curves (B) and (C) were fitted according Hertz’s model (green) and linear model (magenta) to calculate elasticity modulus and kB, respectively. By combining properly the Hertz’s model and Hooke’s law, nanomechanical properties of the bacterial envelope can be deduced from the experimental loading force-indentation curves.