Multiscale dynamics of the cell envelope of Shewanella putrefaciens as a response to pH change.

The bacterial surface properties of gram-negative Shewanella putrefaciens were characterized by microbial adhesion to hydrocarbons (MATH), adhesion to polystyrene dishes, and electrophoresis at different values of pH and ionic strength. The bacterial adhesion to these two apolar substrates shows significant variations according to pH and ionic strength. Such behavior could be partly explained by electrostatic repulsions between bacteria and the solid or liquid interface.

Surface structure and nanomechanical properties of Shewanella putrefaciens bacteria at two pH values (4 and 10) determined by atomic force microscopy.

The nanomechanical properties of gram-negative bacteria (Shewanella putrefaciens) were investigated in situ in aqueous solutions at two pH values, specifically, 4 and 10, by atomic force microscopy (AFM). For both pH values, the approach force curves exhibited subsequent nonlinear and linear regimens that were related to the progressive indentation of the AFM tip in the bacterial cell wall, including a priori polymeric fringe (nonlinear part), while the linear part was ascribed to compression of the plasma membrane. These results indicate the dynamic of surface ultrastructure in response to changes in pH, leading to variations in nanomechanical properties, such as the Young's modulus and the bacterial spring constant.