A voltage-sensitive fluorescent protein has revealed, at the single-cell level, the electrical signals that bacteria use to eject compounds.

The electrical potential across biological membranes drives the transport of some molecules into and out of cells, but measuring this voltage difference in bacteria has proved difficult. Adam Cohen and his colleagues at Harvard University in Cambridge, Massachusetts, modified the marine bacterial protein proteorhodopsin so that it fluoresced in response to voltage changes. They then expressed the engineered protein in the bacterium Escherichia coli.

When the bacteria were exposed to a membrane-permeable dye, flashes of fluorescence coincided with precipitous decreases in the amount of dye in the cell. This suggests that the dye is pumped out of the cell in response to electrical signals.

Science 333, 345–348 (2011)