How do bacteria deal with extreme pressures and pressure changes?

The bacterial cell wall supports a multitude of transport and sensory functions, but also serves as a tough container, containing turgor pressures around 1 atm in gram-negative bacteria and up to 20 atm in gram-positive bacteria. Mechanical stretch stiffness and shape maintenance are provided by the covalently linked peptidoglycan (PG) layer that is nevertheless an active material, undergoing constant growth. Mechanosensitive channels in bacteria serve as emergency valves, releasing osmolytes when increased turgor pressure threatens to damage the cell wall. We have developed an AFM-based method to measure cell response to mechanical challenge, to track turgor pressure and to observe channel gating in living cells. We model the PG layer of E. coli as an anisotropic elastic network composed of two types of nonlinear springs (glycans and oligopeptides). We vary structural properties such as glycan length distribution, angular distribution, and cross-link density (pore size distribution) to accurately reproduce observed mechanical properties such as stress-strain relationships (elastic moduli), strain and stress ratios between axial and hoop directions.