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Originally published as Biophys J. BioFAST on October 14, 2005.
doi:10.1529/biophysj.105.071332
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Biophysical Journal 90:357-365 (2006)
© 2006 The Biophysical Society

Fluorescence Measurement of Intracellular Sodium Concentration in Single Escherichia coli Cells

Chien-Jung Lo, Mark C. Leake and Richard M. Berry

Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom

Correspondence: Address reprint requests to Richard M. Berry, E-mail: r.berry{at}physics.ox.ac.uk.

The energy-transducing cytoplasmic membrane of bacteria contains pumps and antiports maintaining the membrane potential and ion gradients. We have developed a method for rapid, single-cell measurement of the internal sodium concentration ([Na+]in) in Escherichia coli using the sodium ion fluorescence indicator, Sodium Green. The bacterial flagellar motor is a molecular machine that couples the transmembrane flow of ions, either protons (H+) or sodium ions (Na+), to flagellar rotation. We used an E. coli strain containing a chimeric flagellar motor with H+- and Na+-driven components that functions as a sodium motor. Changing external sodium concentration ([Na+]ex) in the range 1–85 mM resulted in changes in [Na+]in between 5–14 mM, indicating a partial homeostasis of internal sodium concentration. There were significant intercell variations in the relationship between [Na+]in and [Na+]ex, and the internal sodium concentration in cells not expressing chimeric flagellar motors was 2–3 times lower, indicating that the sodium flux through these motors is a significant fraction of the total sodium flux into the cell.




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