Mechanical Properties of the Coat Protein Layer and Cortex in Single Bacillus subtilis Spores Studied with an Atomic...

The differences in the mechanical properties between the cortex and coat protein layer in a Bacillus subtilis spore were clarified using an atomic force microscope (AFM) and an originally developed laser-induced surface deformation (LISD) microscope. AFM force curve measurements show that the Young's modulus of the coat protein layer is ca. 66% lower compared with that of the cortex. It has been experimentally clarified that the cortex makes a greater contribution to the rigidity of spores than the coat protein layer. From comparisons of the LISD power spectra, it is revealed that the coat protein layer has two different viscoelastic regions, and that the cortex relatively has a higher viscous nature than the coat protein layer. Furthermore, the LISD power spectrum above 1 × 10⁵ Hz in the coat protein layer suggests that the local region in the coat protein layer behaves as a more elastic body compared with the cortex.