Theory of large-bead AFM compression of pressurized rod-shaped bacteria

A theory for large-bead AFM compression of pressurized spherocylindrical bacteria shows force–displacement curves are dominated by cell geometry and turgor pressure, with envelope elasticity only higher-order.

• Why it matters: AFM measurements of living bacteria need a quantitative way to infer turgor pressure from force–displacement data, accounting for how probe size and cell shape affect the mechanics.
• What they did: They model pressurized spherocylindrical cells compressed by spherical probes with radius much larger than the cell radius, using numerical simulations plus analytical theory to fit AFM curves.
• The result: The leading-order response is approximated by a tension-dominated cross-sectional description, with finite aspect ratio and probe curvature handled via geometric renormalizations, enabling turgor-pressure extraction and deformation-shape prediction.

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