AqpZ-mediated water permeability in Escherichia coli measured by stopped-flow spectroscopy

Abstract

We report that the water permeability of wild-type Escherichia coli during exponential growth is comparable to that of an aqpZ disruption mutant. In contrast, an increase in permeability is observed for the wild type at the onset of the stationary stage with no significant corresponding change in the permeability of the mutant.

FIG. 1.

Growth (open circles) of (A) MG1655 (wild type) and (B) NCM3306 (ΔaqpZ::Cam⁺) in LB with aeration at 37°C (optical density at 600 nm [OD₆₀₀]) and osmotic permeability (open squares) for the efflux of water from cells suspended in PBS (100 mM Na_xPO₄, pH 7.4) upon 1:1 mixing with 1 M l-proline (in the same PBS) at 5°C as a function of time. The cultures were started by 1:100 dilution of a 15-h culture with fresh LB medium.

FIG. 2.

Growth (open circles) of MG1655 (wild type) in LB with aeration at 37°C (optical density at 600 nm [OD₆₀₀]) during the exponential phase of growth and osmotic permeability (open squares) for the efflux of water from cells suspended in PBS (100 mM Na_xPO₄, pH 7.4) upon 1:1 mixing with 1 M l-proline (in the same PBS) at 37°C as a function of time. The line was generated by least-squares fit of the growth data (which yields a generation time [g] of 30 min).