Direct measurement of cell wall stress-stiffening and turgor pressure in live bacterial cells

TL;DR

This study uses atomic force microscopy to measure how E. coli cell walls stiffen under stress and to quantify the internal turgor pressure, revealing power-law stress-stiffening behavior and specific stiffness and pressure values.

Contribution

It provides the first direct measurements of stress-stiffening and turgor pressure in live bacterial cells, distinguishing contributions of cell wall mechanics and internal pressure.

Findings

E. coli cell wall exhibits power-law stress-stiffening with an exponent of 1.22

The axial and circumferential cell wall stiffness are 23 MPa and 49 MPa

Turgor pressure in living E. coli cells is approximately 29 kPa

Abstract

We study intact and bulging Escherichia coli cells using atomic force microscopy to separate the contributions of the cell wall and turgor pressure to the overall cell stiffness. We find strong evidence of power-law stress-stiffening in the E. coli cell wall, with an exponent of 1.22 \pm 0.12, such that the wall is significantly stiffer in intact cells (E = 23 \pm 8 MPa and 49 \pm 20 MPa in the axial and circumferential directions) than in unpressurized sacculi. These measurements also indicate that the turgor pressure in living cells E. coli is 29 \pm 3 kPa.