E. coli are electric creatures. This bacterium, which lives in the human gut, creates its own electrical spikes, and scientists have now devised a way to watch the cells blink on as they spike, then blink off.
While it was already known that the large populations of these cells, on average, tended to maintain a negative charge within their membranes, scientists couldn't tell what the individual cells were up to.
Now, by altering a light-capturing protein found in marine microorganisms and inserting it into the E. coli, researchers could see single cells change their electrical state for the first time.
Like other living things, E. coli are capable of creating a difference in electric potential, or voltage, by pumping charged ions, like sodium and potassium, through their cellular membranes (the outer covering of the cell). A similar process allows our nerves to send messages within our bodies in the form of electrical spikes.
The difference between the electrical charge within the cell's membrane and the outside environment plays an important role in the cell's ability to create energy-storage molecules, driving the motion of its tail, or flagellum, and transporting other molecules through the cellular membrane, according to study researcher Adam Cohen, associate professor in the chemistry and physics department at Harvard University.
Originally, the researchers were looking for a way to visualize electrical changes in mammalian cells. They altered the light-capturing protein so it would emit light as the electrical difference changed outside the membrane versus inside the membrane.
"Then one day, [postdoctoral researcher Joel Kralj] looks at the E. coli in the microscope. He said 'Holy cow, they are blinking.' And that was not something we expected to find at all," Cohen said.
In fact, the video they captured (above) showed individual cells lighting up for between 1 and 40 seconds before darkening again. The dark phase, which could last for minutes at a time, is associated with a more negative charge within the cell, Cohen said.
Preliminary research indicates that the blinking may happen as the cell pumps out potential contaminants. This pumping action is a common mechanism of antibiotic resistance, since some bacterial cells will pump out the antibiotics meant to kill them. So this technique could provide a new way to study antibiotic resistance, Cohen said.
The team also found that the blinking could be altered: For instance, the cells blinked faster when exposed to an acidic environment and slowed down in a more basic environment, stopping altogether when conditions went too far in either direction.
Their work appears in the July 15 issue of the journal Science.
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