Hey, You Talking to Me?
Shewanella oneidensis, or “Shewie,” is a bacteria that lives in places like your backyard or Lake Oneida in upstate New York.
One of these rod-like bacteria by itself is not terribly impressive, but as a group, it has the potential to do things like power drug delivery nanobots or pacemakers in your body, or turn wastewater treatment plants into power plants.
The key, of course, is Shewie’s single superpower: its ability to move electrons long distances, even outside its own body. Indeed, sharing electrons is at the heart of much of modern life, whether it’s a microchip that allows us to hear “Hey, Jude” or the very eating and breathing living things take for granted.
Shewie, it’s now suspected, may even share electrons to “talk” with its fellow bacteria.
The answers might lie in a rather unique USC collaboration between an engineer, Urbashi Mitra, an expert in communication networks, and a scientist, Moh El-Naggar, an expert in biophysics.
“We’re doing something that no one, to my knowledge, is doing,” said El-Naggar, a USC Dornsife assistant professor of physics. “We’re applying communication theory to networks of bacteria.”
But some key questions loom: If these bacteria are talking, conceivably firing a million electrons a second at one another, can we predict how many electrons they will share, and under what circumstances? Might we corral enough electrons to power our tiny devices?
Communication theory, in Mitra’s case, has traditionally been applied to the world of radio and cell phones. Mitra’s group works on the design and analysis of complex wireless communication systems. If you’re in Los Angeles, calling your grandmother in Duluth, you have to worry about things like “fidelity of information.” That is, did Grandma in Duluth hear exactly what I said two thousand miles away?
Consider Samuel Morse and the original telegraph. Back in 1844, he invoked the Bible, Numbers 23:23, to send the very first telegraph message—“What hath God wrought?”—from Washington, D.C., to Baltimore. But what happened when the distance was more than a couple hundred miles? What happened if the message is more complicated than “What hath God wrought?”
Morse knew that it was pure physics; the signal strength would be reduced as a function of the distance and the amount of data. So he imagined something new, the Morse Telegraph Repeater, a series of relay stations in every city that would duplicate the original message and pass them along to the next station.
When Mitra heard about the “big news” in microbial research, it sounded an awful lot like the engineered wireless networks she’s been exploring these past 20 years.
According to El-Naggar, scientists have known for some time that bacterial cells share chemical signals back and forth in close proximity. But in 2012, deep in the ocean, scientists discovered something astonishing: thousands of bacterial cells, chains as long as a centimeter, had formed naturally in the wild.
Like Morse’s telegraph repeater, they were relaying information. Imagine for a moment, this Empire State Building of bacteria, submerged beneath the ocean floor. Each end of the tower has something the other side wants: the bacteria buried deepest in the soil have energy and hydrogen sulfide, but no oxygen. The bacteria nearest to the water have oxygen, but no energy.
The whole community of bacteria has to work together to move electrons from one end to another.
Was this sharing of electrons just another form of communication? How big a network could they form? How much information could they share? No one had done any mathematical modeling of this multi-hopped bacterial system before. Fortunately, Mitra was fascinated by this idea that communication could be more than the transmission of electromagnetic waves in the air. A key question, according to Mitra is, “Could communication theory be used to explain why these seemingly impossibly long chains of bacteria existed in the wild?”
“Any signal we send out is information,” she said. “There’s this story about how people around (former Secretary of State) Madeline Albright figured out that the brooch she wore to each meeting signaled the mood she was in. I suspect at first, she was doing this unconsciously, but probably towards the end, she exploited it.”
Other species use different forms of communication like waggling-dances by bees to indicate where to find food. It is possible that bacteria also have information to express to each other to maintain the livelihood of the cable. And they’re doing it on a mass scale, thousands of bacteria at a time. The number of electrons received from a neighboring bug can determine the internal workings of the receiving bug so that every bacterium in the chain is happy.
“There’s a lot more microbes on this planet than anything else,” laughed El-Naggar. “We’re talking about defining a whole new way of communication between them.”
Consider the implications in our own bodies, where bacterial cells outnumber human cells by a ratio of three to one. If electron exchange between bacteria is just another mode of communication, El-Naggar explained, “it could be a way of regulating microbes within our own bodies, which could have implications for disease.” Using engineering principles to model bacterial interaction could also have significant implications on how these biological experiments, which are costly and require a lot of human attention, are conducted.
Most bacteria in our bodies do good things, not bad things. For example, mitochondria are ancient bacteria living in a symbiotic relationship with our cells. They generate the power, ATP, for all human life.
But it’s not hard to imagine a scenario where a disease like sepsis is caused by a bacterial communication gone haywire. Like a broken circuit, understanding the whys and hows of bacterial communication might enable new engineering solutions.
From day one, Mitra and her team were forced to abandon classical ideas about how things work in man-made wireless radio communication, in favor of a living, biological system. Critical to the recent success of the collaboration were the efforts of Nicolo Michelusi, a USC Viterbi electrical engineering post-doctoral researcher, and Sahand Pirbadian, a physics graduate student. Michelusi was inspired by his dissertation research on energy harvesting for wireless sensor networks to design models for these bacterial networks. Mitra also found an ally in Paul Bogdan, an expert in statistical physics and USC Viterbi assistant professor in the Ming Hsieh Department of Electrical Engineering. With Bogdan’s computational help, Mitra hopes to move from modeling the communication of tens of bacteria to a network of thousands bacteria within the next year.
Said Mitra: “Once we define the fundamentals and validate the theory via experiment, the applications will be vast.”