2005. Assessment of elasticity and topography of Aspergillus nidulans spores via atomic force microscopy

Previous studies have described both surface morphology and adhesive properties of fungal spores, but little information is currently available on their mechanical properties. In this study, atomic force microscopy (AFM) was used to investigate both surface topography and micromechanical properties of Aspergillus nidulans spores. To assess the influence of proteins covering the spore surface, wild-type spores were compared with spores from isogenic rodA and rodA strains. Tapping-mode AFM images of wild-type and rodA spores in air showed characteristic “rodlet ” protein structures covering a granular spore surface. In comparison, rodA spores were rodlet free but showed a granular surface structure similar to that of the wild-type and rodA spores. Rodlets were removed from rodA spores by sonication, uncovering the underlying granular layer. Both rodlet-covered and rodlet-free spores were subjected to nanoindentation measurements, conducted in air, which showed the stiffnesses to be 110 10, 120 10, and 300 20 N/m and the elastic moduli to be 6.6 0.4, 7.0 0.7, and 22 2 GPa for wild-type, rodA and rodA spores, respectively. These results imply the rodlet layer is significantly softer than the underlying portion of the cell wall. Fungal spores are of importance medically (25), agricultur-ally (9), and industrially (3) and provide fungi a natural means of reproduction, dispersion, and survival in adverse environ