When North Carolina State University's Jiri Hulcr began to study the bacteria and fungi living inside insects, he didn't think that a student's curiosity about whether humans have similar organisms living inside and on them would turn into a serious scientific endeavor. But it did.
"Everybody has a very distinct, and very colorful, and very smelly community of bacteria living on us," Hulcr says. His suggestion that his students smear a piece of skin on a petri dish to see if they could culture their own microbes turned into a lighthearted project swabbing the belly buttons of attendees to a conference in Raleigh, near Hulcr's school. And that, in turn, became a surprisingly significant study of microbial ecology — the Belly Button Biodiversity project. "We swabbed their belly buttons, provided them with photos of their colonies of bacteria, and everybody was excited," Hulcr says. "And so we decided to do this on a much larger scale, and thought, 'If we are popular and people are into it, we can get some more funding, and some more volunteers, and we can actually transform this initially silly project into a very serious study of diversity of bacterial symbionts on humans.'"
Most research done on bacterial symbionts is medical, Hulcr says, with many researchers looking for ways to get around harmful bugs, or to beat the growing problem of antibiotic resistance. But now, he adds, "we're starting to have some idea about the natural diversity of bacteria on healthy human skin. It turns out that it's huge — much, much bigger than you would get if you just read the medical journals."
Hulcr and his team decided to take the swabs from their initial 95 volunteers and sequence them. They were hoping to get an idea of the diversity that exists in people's microbial communities, and whether the differences between people could be pegged to which city or state they were from, or other variables that might dictate what bacteria lived on and in them. "We don't know what makes some people have a lot of Staphylococcus, and some other people have lot of other bacteria," Hulcr says. "And those communities are stable on people throughout our lives for the most part, so there must be some fairly strong selection pressure on maintaining these communities."
From the first sequencing run, the team found an unexpected 1,400 strains of bacteria, 662 of which couldn't be classified. As it turns out, very few of the bacteria Hulcr's team swabbed from their volunteers' navels could be cultured, and it took DNA sequencing to see the diversity present. "They really need the person, they really need the skin, and so they live on us, but we can't really culture them," Hulcr says. "So that's why it was a surprise, because … when you actually scan the complete diversity with a sequencing approach, then it's a jungle."