Bacteria Create Electrical Spikes

Bacteria exhibit spontaneous electrical spiking behavior that may be similar to neuron firing, reported Harvard University's Adam E. Cohen on Monday at the ACS national meeting in Boston.

Cohen and colleagues were working with proteorhodopsin, a protein that turns sunlight into energy in some microbes by moving a proton from one side of the cell membrane to the other. Ion transport across membranes creates a membrane potential, or a difference in voltage between the outside and inside of a cell. The researchers were trying to engineer the protein to essentially run in reverse--to change its fluorescence emission in response to a change in cellular voltage--as a means to image electrical activity in neurons.

They succeeded. When they initially expressed the mutated protein in Escherichia coli, they observed the proteins flashing on and off "a little bit like fireflies," Cohen said. Some flashed periodically and some irregularly; some lit up for longer and some for shorter periods of time.

Cohen's use of proteorhodopsin is "a very interesting modality for how to observe the state of a cell," says Ed Boyden, a neurobiologist at Massachusetts Institute of Technology. As for the electrical activity in bacteria, that could be a previously unrecognized form of bacterial signaling, he says.

Cohen and colleagues are now trying to pin down the source and purpose of the bacterial voltage fluctuations. They are also working to express the protein in eukaryotic cells for neuron imaging.