Despite the parallels to neural activity, Süel emphasizes that biofilms are not just like brains. Neural signals, which rely on fast-acting sodium channels in addition to the potassium channels, can zip along at more than 100 meters per second — a speed that is critical for enabling animals to engage in sophisticated, rapid-motion behaviors such as hunting. The potassium waves in Bacillus spread at the comparatively tortoise-like rate of a few millimeters per hour. “Basically, we’re observing a primitive form of action potential in these biofilms,” Süel said. “From a mathematical perspective they’re both exactly the same. It’s just that one is much faster.”

Bacterial Broadcasting

Süel and his colleagues had more questions about that electric signal, however. When the wave of potassium-driven electrical activity reaches the edge of a biofilm, the electrical activity might stop, but the cloud of potassium ions released into the environment keeps going. The researchers therefore decided to look at what happens once the potassium wave leaves a biofilm.

The first answer came earlier this year in a Cell paper, in which they showed that Bacillus bacteria seem to use potassium ions to recruit free-swimming cells to the community. Amazingly, the bacteria attracted not only other Bacillus, but also unrelated species. Bacteria, it seems, may have evolved to live not just in monocultures but in diverse communities.

A few months later, in Science, Süel’s team showed that by exchanging potassium signals, two Bacillus biofilms can “time-share” nutrients. In these experiments, two bacterial communities took turns eating glutamate, enabling the biofilms to consume the limited nutrients more efficiently. As a result of this sharing, the biofilms grew more quickly than they could have if the bacteria had eaten as much as they could without interruption. When the researchers used bacteria with ion channels that had been modified to give weaker signals, the biofilms, no longer able to coordinate their feeding, grew more slowly.

Süel’s discoveries about how bacteria communicate electrically have exhilarated bacteria researchers.

“I think it’s some of the most interesting work going on in all of biology right now,” said Moh El-Naggar, a biophysicist at the University of Southern California. El-Naggar studies how bacteria transfer electrons using specialized thin tubes, which he calls nanowires. Even though this transfer could also be considered a form of electrical communication, El-Naggar says that in the past, he would “put the brakes on” if someone suggested that bacteria behave similarly to neurons. Since reading Süel’s 2015 paper, he’s changed his thinking. “A lot of us can’t wait to see what comes out of this,” he said.

For Gemma Reguera, a microbiologist at Michigan State University, the recent revelations bolster an argument she has long been making to her biologist peers: that physical signals such as light, sound and electricity are as important to bacteria as chemical signals. “Perhaps [Süel’s finding] will help the scientific community and [people] outside the scientific community feel more open about other forms of physical communication” among bacteria, Reguera said.

Part of what excites researchers is that electrical signaling among bacteria shows signs of being more powerful than chemically mediated quorum sensing. Chemical signals have proved critical for coordinating certain collective behaviors, but they quickly get diluted and fade out once they’re beyond the immediate vicinity of the bacteria emitting the signal. In contrast, as Süel’s team has found, the potassium signals released from biofilms can travel with constant strength for more than 1,000 times the width of a typical bacterial cell — and even that limit is an artificial upper bound imposed by the microfluidic devices used in the experiments. The difference between quorum sensing and potassium signaling is like the difference between shouting from a mountaintop and making an international phone call.

Moreover, chemicals enable communication only with cells that have specific receptors attuned to them, Wingreen noted. Potassium, however, seems to be part of a universal language shared by animal neurons, plant cells and — scientists are increasingly finding — bacteria.

A Universal Chemical Language

“I personally have found [positively charged ion channels] in every single-celled organism I’ve ever looked at,” said Steve Lockless , a biologist at Texas A&M University who was Süel’s lab mate in graduate school. Bacteria could thus use potassium to speak not just with one another but with other life-forms, including perhaps humans, as Lockless speculated in a commentary to Süel’s 2015 paper . Research has suggested that bacteria can affect their hosts’ appetite or mood; perhaps potassium channels help provide that inter-kingdom communication channel.

The fact that microbes use potassium suggests that this is an ancient adaptation that developed before the eukaryotic cells that make up plants, animals and other life-forms diverged from bacteria, according to Jordi Garcia-Ojalvo, a professor of systems biology at Pompeu Fabra University in Barcelona who provided theoretical modeling to support Süel’s experiments. For the phenomenon of intercellular communications, he said, the bacterial channel “might be a good candidate for the evolutionary ancestor of the whole behavior.”

The findings form “a very interesting piece of work,” said James Shapiro, a bacterial geneticist at the University of Chicago. Shapiro is not afraid of bold hypotheses: He has argued that bacterial colonies might be capable of a form of cognition. But he approaches analogies between neurons and bacteria with caution. The potassium-mediated behaviors Süel has demonstrated so far are simple enough that they don’t require the type of sophisticated circuitry brains have evolved, Shapiro said. “It’s not clear exactly how much information processing is going on.”

Süel agrees. But he’s currently less interested in quantifying the information content of biofilms than in revealing what other feats bacteria are capable of. He’s now trying to see if biofilms of diverse bacterial species time-share the way biofilms of pure Bacillus do.

He also wants to develop what he calls “bacterial biofilm electrophysiology”: techniques for studying electrical activity in bacteria directly, the way neuroscientists have probed the brain for decades. Tools designed for bacteria would be a major boon, said Elisa Masi, a researcher at the University of Florence in Italy who has used electrodes designed for neurons to detect electrical activity in bacteria. “We are talking about cells that are really, really small,” she said. “It’s difficult to observe their metabolic activity, and there is no specific method” for measuring their electrical signals.

Süel and his colleagues are now developing such tools as part of a $1.5 million grant from the Howard Hughes Medical Institute, the Bill and Melinda Gates Foundation, and the Simons Foundation (which publishes Quanta).

The findings could also lead to new kinds of antibiotics or bacteria-inspired technologies, Süel said, but such applications are years away. The more immediate payoff is the excitement of once again revolutionizing our conceptions about bacteria. “It’s amazing how our understanding of bacteria has evolved over the last couple decades,” El-Naggar said. He is curious about how well potassium signaling works in complex, ion-filled natural settings such as the ocean. “Now we’re thinking of [bacteria] as masters of manipulating electrons and ions in their environment. It’s a very, very far cry from the way we thought of them as very simplistic organisms.”

“Step by step we find that all the things we think bacteria don’t do, they actually do,” Wingreen said. “It’s displacing us from our pedestal.”

This article was reprinted on ScientificAmerican.com.