RESUMEN
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. However, a similar trend was also observed at rather high ionic strength where electrostatic interactions are supposed to be screened. The nanomechanical properties at pH 4 and 10 and at high ionic strength were investigated by using atomic force microscopy (AFM). The indentation curves revealed the presence of a polymeric external layer that swells and softens up with increasing pH. This suggests a concomitant increase of the water permeability and so did of the hydrophilicity of the bacterial surface. Such evolution of the bacterial envelope in response to changes in pH brings new insight to the pH dependence in the bacterial adhesion tests. It especially demonstrates the necessity to consider the hydrophobic/hydrophilic surface properties of bacteria as not univocal for the various experimental conditions investigated.
Asunto(s)
Shewanella putrefaciens/metabolismo , Adhesión Bacteriana , Fenómenos Biomecánicos , Fenómenos Biofísicos , Biofisica , Membrana Celular/química , Membrana Celular/metabolismo , Membrana Celular/ultraestructura , Electroforesis , Hidrocarburos , Concentración de Iones de Hidrógeno , Microscopía de Fuerza Atómica , Microscopía Electrónica , Nanotecnología , Concentración Osmolar , Poliestirenos , Shewanella putrefaciens/química , Shewanella putrefaciens/ultraestructura , Electricidad Estática , Propiedades de Superficie , TermodinámicaRESUMEN
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.
