Elastic Properties of Aspergillus nidulans Studied with Atomic Force Microscopy

摘要

In this study an atomic force microscope (AFM) was used as a nanoindentor to measure cell wall mechanical properties of the model fungus Aspergillus nidulans in both hyphal and spore forms. For fungal hyphae the nanoindentation data were compared to finite element analysis (FEMLAB v3.0, Burlington MA) to simulate AFM indentation because no suitable analytical models were available. The elastic modulus of wild type hyphae grown in complete medium was determined to be 110 ± 10 MPa. This decreased to 64 ± 4 MPa when grown in 0.6 M KCl, implying growth medium osmotic conditions have significant effects on cell wall elasticity. These values are comparable with other microbial systems (e.g., yeast and bacteria). Comparisons with a mutant strain (ΔcsmA) further indicate that the differences in mechanical properties may be dependent on varying molecular structure of hyphal cell walls as opposed to wall composition. AFM images showed characteristic "rodlet" protein structures covering spore surface. This feature can be removed by sonication. Nanoindentation measurements on the spores showed that rodlet-covered spores had surface stiffness of 110 ± 10 N/m and cell wall elastic modulus of 6.6 ± 0.4 GPa, both lower than those of rodlet-free spores. These results imply the rodlet layer is significantly softer than the underlying portion of the cell wall.