Microbiome Monday: The Ecosystem In Your Belly Button

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It's Microbiome Monday again! Before the Museum’s upcoming exhibition The Secret World Inside You opens November 7, we’re offering weekly primers on the microbiome and the research surrounding it from Curators Rob DeSalle and Susan Perkins, as well as from other scientists who are working in this exciting field.

This week, Dr. DeSalle and Dr. Perkins take us on a tour of the marvelous menagerie inside your belly button, which, it turns out is home to much, much more than just the occasional piece of lint.

Belly Button Ecology

The belly button, or umbilicus, starts to form shortly after birth when the umbilical cord is snipped, separating a newborn from its mother. The part of the umbilical cord still attached to the baby forms scar tissue that in about 90 percent of the population folds back in on itself in such a way that the baby has an “innie.” The other 10 percent of the population scars in a different way, forming the less familiar “outie.” Because of the way the umbilical cord is attached and the way the cut cord heals, the belly button can take on many different shapes, such as being T-shaped, oval, or a vertical slit. From size to shape to depth, the topology of the belly button can vary widely from person to person. But belly button diversity doesn’t end there—the “ecology” of belly buttons will vary wildly too.

Belly Button
Your belly button is home to an astonishing array of microbial life.
Courtesy of Wikimedia Commons

While scientists have researched things like how belly buttons affect attraction (most men seem to prefer shallow “innies,” according to one Finnish study), the most spectacular belly button research is on the microbial biodiversity inside them. In 2012, Rob Dunn and his colleagues at North Carolina State University examined the belly buttons of science writers who had attended scientific meetings in the area, and compared the belly buttons of people who attended a scientific conference a month later. Their paper, appropriately entitled “A Jungle in There: Bacteria in Belly Buttons are Highly Diverse, But Predictable,” describes the results of using next-generation sequencing approaches to determine the number and kinds of bacteria living in the belly buttons of the 60 people in the study from the two different events. Their findings show that the diversity of belly button aesthetics pales in comparison to the diversity of belly button microbe populations. 

The diversity that the researchers observed was spectacular—in the 60 different belly buttons surveyed, they found a total of nearly 2,400 phylotypes (a phylotype is shorthand in microbiome studies for “species”) of bacteria. The vast majority of these phylotypes (2,188) were found in fewer than 10 percent of the belly buttons studied. Even though there were 200 or so phylotypes found in more than 10 percent of the belly buttons, none of these were found in all belly buttons, and only eight phylotypes are found in more than 70 percent of the belly buttons.

The authors of the work suggest that the belly button biodiversity is on par with the animal diversity in a jungle. A more complete understanding of belly button ecology and microbial diversity is forthcoming, but what we know so far is quite surprising.

This post is adapted from Dr. DeSalle's and Dr. Perkins's forthcoming book Welcome to the Microbiome: Getting to Know the Trillions of Bacteria and Other Microbes In, On, and Around You from Yale University Press.