Your Body Is Surrounded by Clouds of Skin and Fart Bacteria
Everywhere you go, in everything you do, you are surrounded by an aura of microbes. They drift down from your hair when you scratch your head, they fly off your hand when you wave to your friend, they spew out of your mouth when you talk. Even when you sit around doing nothing, you’re sitting in your own, personal microbial bubble.
Made up of millions, billions, trillions of bacteria, yeast, cells, and cell parts, this bubble is actually more like a cloud—a cloud, new research suggests, that is unique to you. And as gross as it is to imagine everyone around you shedding microbial bits and pieces into the air, studying those clouds can be useful for people like doctors tracking down disease outbreaks and cops tracking down criminals.
The gut microbiome, often invoked in expensive probiotic-heavy diets, is probably the hottest microscopic community right now. It’s the collection of microbiota, living inside you, that helps you break down food, fight disease, and control your hunger.
But your outer body has its own microbiome, too. Your body is covered in skin, and that skin is like a vast savannah populated with millions of exotic critters. They feed on the oils seeping from your skin, dead cells, bits of organic matter, and each other. “In a single centimeter of skin, you can find thousands of bacteria,” says James Meadow, former Oregon State University researcher and co-author of a microbiome paper published today in the journal PeerJ.
Combined, the non-you cells in your body outnumber the you cells by about 10 to one. And if some sadistic scientist were to grind up and sequence all the DNA in every cell in and on your body, only about 2 percent of the genetic material would be human. The rest is microbes.
Your microbiome cloud is what happens when your body liberates those gut and skin microbes. “If I scratch my head, thousands of skin cells, cell fragments, bacteria, and fungi get airborne,” says Meadow. When you pick your nose, burp your ABCs, or signal your compliments to the chef, gut microbes join the cloud. And, sorry if you were eating, but your farticles are also a medium for all the gut microbes living in you. Quoting Stanford microbiologist Stanley Falkow, Meadow says, “The world is covered in a fine patina of feces.”
Meadow and his co-authors wanted to know if this combined cloud was detectable, and whether its DNA signature varied significantly between individuals. So they did a pair of experiments, both involving people sitting in sterilized rooms.
In the first, each of the subjects sat for four hours playing on a laptop while a circle of air filters captured their bacterial clouds. The researchers collected the screens and used chemicals to burn away everything except their DNA.
After they saw how much data they’d gotten in the first experiment, the scientists decided to repeat it with more volunteers. These second experiments were exactly the same, except the volunteers only spent 90 minutes in the room, and the researchers collected samples with floor dishes instead of screens. (The researchers used interstitial experiments to show the floor dishes captured roughly the same thing).
Now, bacteria easily get stirred up the currents and eddies you create as you walk around. “If you are close enough to shake hands with someone, you are in their microbial cloud,” says Meadow. “When someone walks by and you feel breeze, that’s taking your bacteria with them.” That means you share microbes with your coworkers, your family members, and the people you ride the train with.
So how different could individuals’ microbial clouds really be? The two trials showed that, at least in these 11 people, microbial clouds varied significantly from person to person. They also found that different people shed microbes at different rates.
“We know that every person has this unique microbiome profile and that they shed it into the environment,” says Jack Gilbert, a microbiologist at Argonne National Laboratory who has done a lot of work looking at microbial clouds. This study is the first to pare that uniqueness down to the genetic level.
That knowledge will help shape microbiome cloud research in fields like contagious disease and forensics. In hospitals, nobody really knows how germs spread. Since leaving Oregon State University, Meadow has joined a biotech company in San Francisco that wants to use the understanding of microbial clouds to help hospitals prevent things like MRSA outbreaks.
Cops see other opportunities for the microbial cloud. Gilbert has been helping crime scene investigators use microbial residue to track down criminals. He says people pick up microbes from the soil, the air, the food they eat, and the water they wash and drink with. So an individual’s unique microbial signature could put them at the scene of a crime—or exonerate them if the microbes in their cloud match their alibi.
At least, in theory. “That would rely on a much more extensive database than currently exists,” says Gilbert. With the Earth Microbiome Project, Gilbert is building a biogeographic database to fill in the gaps. So in a few years, scientists won’t have to drill down into your DNA to figure out what is you. Like Pigpen from Peanuts, you’ll carry a fog of identity wherever you go.