Surface properties of microbial cells probed at the nanometre scale with atomic force microscopy

Atomic force microscopy (AFM) was used to characterize, under water, the su rface morphology and molecular interactions of two types of microbial cells : fungal spores (Phanerochaete chrysosporium) and bacteria (Lactococcus lac tis), High-resolution deflection images showed that the spore surface was u niformly covered with patterns of rodlets that were several hundred nanomet res in length and had a periodicity of similar to 10 nm, Such surface organ ization was not detected on the bacterial surface, which showed a sponge-li ke structure. Force-distance curves revealed very different molecular inter actions for the two microorganisms: upon approach, no significant curvature was seen in the contact region for spores, contrary to bacteria, pointing to a difference in cell softness; and upon retraction, no adhesion forces w ere detected on spores but multiple unbinding events and elongation forces attributed to macromolecular bridging were observed on bacteria. These resu lts show that AFM is a powerful tool for probing the surface properties of native microbial cells on the nanometre scale. Copyright (C) 2000 John Wile y & Sons, Ltd.