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

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Science  15 Jul 2011:
Vol. 333, Issue 6040, pp. 345-348
DOI: 10.1126/science.1204763

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Introducing Bacterial Electrophysiology

Bacterial electrophysiology has been limited by the inability to measure the membrane potential of single cells. Kralj et al. (p. 345) engineered a class of voltage-sensitive fluorescent membrane proteins to perform electrophysiological measurements on individual intact bacteria. These measurements showed that Escherichia coli generate electrical spikes, reminiscent of action potentials in neurons. The response of electrical spiking in bacteria was assessed in response to a wide range of physical and chemical perturbations, and was correlated with efflux activity. In the future, the probe should be useful in determining the roles of membrane potential in a variety of medically, environmentally, and industrially important bacteria.

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.

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