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Science 333 (6040): 345-348

Copyright © 2011 by the American Association for the Advancement of Science

Electrical Spiking in Escherichia coli Probed with a Fluorescent Voltage-Indicating Protein

Joel M. Kralj,1 Daniel R. Hochbaum,2 Adam D. Douglass,3 Adam E. Cohen1,4,*

Abstract: Bacteria have many voltage- and ligand-gated ion channels, and population-level measurements indicate that membrane potential is important for bacterial survival. However, it has not been possible to probe voltage dynamics in an intact bacterium. Here we developed a method to reveal electrical spiking in Escherichia coli. To probe bacterial membrane potential, we engineered a voltage-sensitive fluorescent protein based on green-absorbing proteorhodopsin. Expression of the proteorhodopsin optical proton sensor (PROPS) in E. coli revealed electrical spiking at up to 1 hertz. Spiking was sensitive to chemical and physical perturbations and coincided with rapid efflux of a small-molecule fluorophore, suggesting that bacterial efflux machinery may be electrically regulated.

1 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
2 Applied Physics Program, School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
3 Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
4 Department of Physics, Harvard University, Cambridge, MA 02138, USA.

* To whom correspondence should be addressed. E-mail: cohen{at}

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