Stretching cell surface macromolecules by atomic force microscopy

We report the first quantitative measurement of macromolecular stretching a t the surface of living cells using combined atomic force microscopy imagin g and force spectroscopy. The surface of dormant spores of Aspergillus oryz ae was covered with a layer of crystalline-like nanostructures (rodlets) an d showed no/weak adhesion forces. By contrast, the surface of germinating s pores consisted of soft granular material, attributed to cell surface polys accharides, and elongation forces reflecting macromolecular stretching were observed in the force-extension curves. These elongation forces were well described by an extended freely jointed chain model with a Kuhn length of 3 .2 +/- 0.9 Angstrom and a segment elasticity of 3.9 +/- 1.8 N/m, which are consistent with values reported for the elastic deformation of single dextr an and amylose polysaccharides. We therefore suggest that the elongation fo rces measured on germinating spores are due to the stretching of cell surfa ce polysaccharides.