In February, biologists and science communicators from North Carolina State University and the North Carolina Museum of Natural Sciences began collecting swabs of bacteria from people’s belly buttons to find out what microorganisms their bodies were hosting.
After getting belly button swabs at science events in North Carolina and from science bloggers, the researchers have finished their first analysis.
In just 95 cultures, they’ve found 1,400 bacterial strains, 662 of which cannot even be grouped to the biological classification of family, “which strongly suggests that they are new to science,” team leader Jiri Hulcr of North Carolina State University told New Scientist. (The order of biological classification goes kingdom, phylum/division, class, order, family, genus, species.)
While it appears belly button bacteria can be diverse, a core group of about 40 species accounts for about 80% of all the bacteria in our belly buttons. This is astounding considering that the world’s microbes outnumber all the species in the animal kingdom.
The New York Times science writer and Discover blogger Carl Zimmer found that his belly button is home to 53 species, which he was told is a “whopping” number.
Only a small fraction of my belly button bacteria were common among the other 89 volunteers. The microbes I share with most other volunteers tend to be ordinary skin dwellers that are typically harmless … But out of 53 species, 35 were present in only 10 or fewer other volunteers. And 17 species in my navel didn’t show up in anyone else. In the column for notes in [the researcher's] spreadsheet, he’s annotated these species with scientific descriptions like “weird one” and “totally crazy.”
It seems Zimmer was not the only subject with strange belly button bacteria: Incredibly, a few sequences of DNA were so unusual that the only conclusion the scientists could make about them were that they are bacteria.
The researchers limited themselves to analyzing DNA from bacteria, choosing to exclude fungi, viruses and other microorganisms.
But just identifying the bacteria alone is a challenge. The scientists had the swabs’ “DNA barcodes” read (meaning that sequences of the gene for 16S ribosomal RNA were read) to help study the evolutionary relationships between the bacteria. They then compared these sequences to millions of DNA sequences in public databases.
However, the smallest unit by which scientists could match these barcodes was 16S ribosomal RNA gene sequences that differed by 3% or less — which, in mammals, would be like lumping dogs and cats together taxonomically.
For belly button bacteria research, it means that two strains that “match” taxonomically — such as a belly button strain and a species recognized as inhabiting the deep ocean — could actually be separated by several million years of evolution.
New frontier in microbiology
The astonishing number of new microbes discovered in the very beginning stages of this belly button experiment reflects how ignorant we are of microbial diversity.
According to New Scientist:
the inhabitants of our navels seem weird because biologists haven’t sampled sufficiently extensively to document the full diversity of microbial life in a variety of habitats. [Hulcr] likens reactions to the first round of belly button results to the astonishment of the first European explorers seeing African big game — which today seem commonplace. ‘Now you’re expecting rhino and elephants,’ Hulcr says.
While the bacterial cultures will never be quite as exciting as rhino or elephants, it is interesting to see how different the cultures look.