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October 6, 2011Open Access

Direct Measurement of Cell Wall Stress Stiffening and Turgor Pressure in Live Bacterial Cells

YDYi DengUniversity of Washington MSMingzhai SunUniversity of Science and Technology of China JSJoshua W. ShaevitzPrinceton University

Key Points

The aim is to measure the contributions of the cell wall and turgor pressure to cell stiffness in E. coli.
Utilized atomic force microscopy to assess mechanical properties in live E. coli cells.
Compared properties between intact cells and unpressurized sacculi.
Measured stiffness in axial and circumferential directions.
Found cell wall stiffness of 23±8 MPa and 49±20 MPa in intact cells across axial and circumferential directions.
Confirmed power-law stress stiffening in the cell wall with an exponent of 1.22±0.12.
Measured turgor pressure in living E. coli at 29±3 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±0.12, such that the wall is significantly stiffer in intact cells (E=23±8 MPa and 49±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±3 kPa.

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