What Lives in Your Belly Button? Study Finds "Rain Forest" of Species

Thousands of bacteria found in navels. "It's quite beautiful," researcher says.

Rob Dunn and his team of ecologists aren't your average navel gazers. They're professional navel gazers, thank you very much, and their new study details the microbial contents of 60 volunteers' belly buttons.

The upshot? Belly buttons, it turns out, are a lot like rain forests.

The whole thing started about two years ago. An undergrad's only-in-a-biology-lab idea—sampling colleague's navel bacteria for a holiday card—struck a chord with the North Carolina State University team, which had adopted a new focus on citizen science.
What better way to get the public interested in science than by showing them their skin's own thriving ecosystems? "And belly buttons are just ridiculous enough to appeal to almost everyone," Dunn added.
What's more, given the belly button's status as one of the body's most rarely scrubbed crannies, it offered researchers a chance to study as close to a pristine microbial landscape as is possible on the modern human.
So in early 2011 the team set up shop at the ScienceOnline science communicators' conference and at the North Carolina Museum of Natural Sciences. The researchers handed out swabs to 60 intrigued, if grossed out, volunteers. Back to the lab, the scientists examined the genetic makeup of their bacterial loot.
The Belly Button Biodiversity project had officially begun.

Welcome to the Jungle
From 60 belly buttons, the team found 2,368 bacterial species, 1,458 of which may be new to science.
Some belly buttons harbored as few as 29 species and some as many as 107, although most had around 67. Ninety-two percent of the bacteria types showed up on fewer than 10 percent of subjects—in fact, most of the time, they appeared in only a single subject.
One science writer, for instance, apparently harbored a bacterium that had previously been found only in soil from Japan—where he has never been.
Another, more fragrant individual, who hadn't washed in several years, hosted two species of so-called extremophile bacteria that typically thrive in ice caps and thermal vents.
(Also see "Armpits Are 'Rain Forests' for Bacteria, Skin Map Shows.")
Despite the diversity, themes emerged.
Even though not a single strain showed up in each subject, eight species were present on more than 70 percent of the subjects. And whenever these species appeared, they did so in huge numbers.
"That makes the belly button a lot like rain forests," Dunn said. In any given forest, he explained, the spectrum of flora might vary, but an ecologist can count on a certain few dominant tree types.
"The idea that some aspects of our bodies are like a rain forest—to me it's quite beautiful," he added. "And it makes sense to me as an ecologist. I understand what steps to take next; I can see how that works."
(Related: "Men's Offices Have More Bacteria, Study Finds.")
Method to the Madness?
But predicting which species might like to call the human body home is only the first step. To make the knowledge useful, scientists need to know why these bacteria show up.
"We're all like the guys before Darwin who went out and brought this stuff on the ship and said, Check out this bird that's totally weird—this has got to be important!
"They were still so far from understanding the big picture," Dunn said. "That's where we are."
(Related: "Drug-Resistant Bacteria Found in Four-Million-Year-Old Cave.")
Hoping to answer those broader questions, Dunn's team is already working on several hundred more navels—soon to be 600. They'll use those new samples to start testing the correlation of the navel dwellers with everything from subjects' places of birth to the makeups of their immune systems.
Making connections such as these could help shed light on the ties between our bacterial hosts and their effects on health. Researchers believe that microbes—not just in the belly button but in every nook and cranny of the human body—are involved in everything from immune function to acne to skin softness. The potential boon to medicine is enormous but out of reach until scientists can clarify what the microbes are doing in the first place, and why they're there.
In the meantime, the lab has kicked off pilot studies for their next citizen-science spectacular: Armpit-pa-looza.
The new Belly Button Biodiversity project study was published November 7 by the journal PLOS ONE. Note: The subject of this story, Rob Dunn, is occasionally hired to write freelance articles for National Geographic magazine, which is affiliated with National Geographic News.