Probing molecular interactions and mechanical properties of microbial cell surfaces by atomic force microscopy

Knowledge of the surface properties of microbial cells is a key to gain a detailed understanding of their functions in the natural environment and to efficiently exploit them in biotechnological processes. In this paper, we present force-distance curves recorded, by atomic force microscopy (AFM) in aqueous solutions, on various microbial samples: reconstituted S-layers, whole fungal spores and several bacterial strains. The approach and retraction curves exhibited important differences--depending on the type of microorganism, on the physiological state (dormancy versus germination) and on the environmental conditions (ionic strength)--which were shown to reflect differences in long-range surface forces, adhesion forces and mechanical properties. These data illustrate the great potential of AFM force measurements to elucidate the physical properties of microbial cells and to understand, at the molecular level, biointerfacial phenomena such as cell adhesion and cell aggregation.