Quantifying the Nanomechanical Properties of Bacillus anthracis and Implications for Spore Killing

摘要

Atomic force microscopy (AFM) was used to study the changes in the nanomechanical properties of the surface of Bacillus anthracis spores during germination. The Hertz model of continuum mechanics of contact was used to evaluate the Young's or tensile elastic modulus of the spores before and after germination by applying the model to load-indentation curves obtained during force cycles. The highest elastic modulus was obtained with dormant spores, with average elasticity values of 197 ± 81 MPa. Fully vegetative spores had the lowest elasticity values. The elasticity decreased when spores were incubated with either L-alanine or inosine, and the decrease was greatest when both of these germinants were used in combination. We also found that as the spore elasticity values increasd, the indentation depth of the AFM probe into the surface increased, with vegetative B. anthracis cells having elasticity depths of up to 246.2 nm. We have shown that spore nanomechanical properties change during germination, and depend on the type of germinant that is used. Weakening of the spore cell wall may help explain why germinating cells are much more susceptible to anti-sporal agents. The study of elasticity of spores may be a valuable tool in the development of antibiotics or anti-sporal treatments.