Stretching cell surface macromolecules by atomic force microscopy

We report the first quantitative measurement of macromolecular stretching at the surface of living cells using combined atomic force microscopy imaging and force spectroscopy. The surface of dormant spores of Aspergillus oryzae was covered with a layer of crystalline-like nanostructures (rodlets) and showed no/weak adhesion forces. By contrast, the surface of germinating spores consisted of soft granular material, attributed to cell surface polysaccharides, 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 dextran and amylose polysaccharides. We therefore suggest that the elongation forces measured on germinating spores are due to the stretching of cell surface polysaccharides.