Lasers can eavesdrop on microbes, including viruses

What do viruses sound like? Scientists recently found out. They developed a way to eavesdrop on these and other microbes. This new tech can help scientists study such microbes and sound out the identity of germs in our environment.

For hundreds of years, we’ve been able to see cells through microscopes. As these spyglasses have gotten more powerful, they’ve been able to zoom in on smaller and smaller details. Yet even when you can see individual microbes, most look pretty similar.

“It’s not a needle in a haystack problem,” says Elad Harel. “It’s a needle in a stack of needles problem.” This chemist works at Michigan State University (MSU) in East Lansing. “To detect one needle from all these other needles,” he says, “you have to look for something that’s unique about it.”

Explainer: What is a virus?

That unique feature could be a sound. Nearly anything can make sound by vibrating — and typically those vibrations get transmitted to our ears through the air. Different things will make distinctive sounds, depending on their shape and what they’re made of. This is why knocking on a table sounds different from tapping on a window.

The same is true for microbes. Each type has its own special makeup of proteins and other molecules. Their unique chemistry and structures give each microbe a characteristic sound.

That’s what led Harel and his MSU team to begin working on their new laser-based system. By figuring out how to measure these sounds, they’re now able to catalog them. It’s much like seeing a distant bird in the woods but not being sure what type of bird it is until you learn its distinctive call.

Harel’s team describes logging such microbial “bird calls” in the January 21 Proceedings of the National Academy of Sciences.

Elad Harel in his lab with some of the equipment that makes up an electronic “ear” that can hear and record the sounds of microbes. P. Henderson, F. Gomez/College of Natural Science MSU

Lasering in  

To measure microbial sounds, Harel’s team started by pointing a laser at a virus. It’s a bit like striking a tiny gong with a teeny mallet — if a mallet could tap a gong millions of times per second.

Those speedy taps set the virus vibrating. The triggered sound waves are far too quiet for our ears to pick up. So Harel’s team measures them with a second laser. The vibrations cause the second laser’s beam to quiver like a very sensitive eardrum. The scientists measure these signals to “hear” the virus.

Other ways of studying microbes, such as viewing them through a microscope, often involve fixing them in place. That makes studying how microbes move a major challenge, notes Kim Davis. A microbiologist, she works at Johns Hopkins University in Baltimore, Md. Usually, what researchers can see is a “snapshot of what is occurring at [one] moment in time,” she says.

With this new tech, scientists may be able to collect data that are less like a freeze-frame and more like a movie of microbes in the environment.

By using sound, “we showed that we can track single viruses and even listen to a virus rupture,” Harel says. As a virus starts to break open, he says, the frequency of its sound begins to drop — “almost like a deflating balloon.”

Learn how the MSU team listens to viruses.

Hard to ID individual strains

There are microbes everywhere. Most aren’t all that dangerous to humans. Consider viruses. Of thousands of species, only about 270 infect people.

But, notes Davis, “It can be very difficult to determine if an organism has pathogenic [illness-provoking] properties just from looking at it.”

With something like the new system, we might one day be able to hear the difference, Harel says.

Explainer: Virus variants and strains

There’s still a lot to learn about these viral sounds, though. The sound a microbe makes might change if it’s on a surface versus in the air (much like how our voices change when we’re underwater). So to “increase our understanding and build a database,” Harel says, “we’ll have to do a lot of experiments on different viruses in different environments.”

Another issue: Many microbes belong to species with lots of related members — strains that you might think of like siblings. Consider E. coli. These bacteria live almost everywhere. Although most are harmless to people, a few strains can cause serious disease. Since all E. coli have nearly the same shape and are made of nearly the same proteins, it might be hard to hear a difference between harmful and harmless ones.

To find out, scientists will have to just keep listening. Once they have a robust library of sounds, they may be able to tell most microbes apart. That because microbial sounds are very specific, Harel says. It’s like listening for a friend’s voice in a loud place. Because their voice is familiar, you can pick it out from the other noises.

There’s plenty of research left to be done. “It’s a new way of looking at biology,” Harel explains. For now, he says, “We don’t know what we’re going to see because very few people have ever looked.”

But one day, this type of tech might prove useful beyond the lab. For instance, it could be used in sensors installed at airports and other crowded places. These could then listen for worrisome microbes — and send out warnings of which ones (and how many) are out there.