Ever wondered about the community of microbes living in your armpit? Or the armpit of a gorilla?
Sarah Council and Julie Horvath have. They and their colleagues recently conducted a census of bacteria and other microbes living in the armpits of humans, gorillas and other primates. It’s a first step toward understanding which microscopic organisms live on our skin and how they help keep us healthy.
Horvath heads up the N.C. Museum of Natural Science’s Genomics and Microbiology Research Lab and is also a research associate professor at N.C. Central. Council is a postdoctoral fellow who also splits her time between the two institutions.
Though microbes live all over us, Council and Horvath focused on armpits, where special glands secrete sweat and oils that bacteria eat. It’s a symbiotic relationship: We provide food and habitat, and the microbes keep pathogens at bay, boost our immune system and perhaps speed the healing of wounds. They also produce odors that strengthen bonds with our mates and children, and may even make us less attractive to mosquitoes.
“We chose armpits because of the large biomass of bacteria there,” said Council, “and because we work in a museum and visitors get excited about unique areas of study.”
Indeed, some museum visitors volunteered their armpits for science – a commitment that involves abstaining from antiperspirant and deodorant for two days then wiping a swab around your armpit.
N.C. Zoo veterinarians took samples from chimps, gorillas and baboons during routine physicals. Collaborators sent samples from rhesus macaques living in a semi-free-ranging population in Puerto Rico.
The researchers used high-speed gene sequencing to analyze a gene called 16S rRNA that’s found in all bacteria and archaea (a group of single-celled organisms). The analysis allowed them to identify the microbes by family or genera.
After crunching the data, Horvath said, “We saw a significant difference between humans and all the other primates.”
The human difference
The microbiome – community of microbes – of the humans was much less diverse. Among humans, about 90 percent of the microbiome was made of four different types of bacteria. In the gorillas and chimps (both apes), those same four types made up a smaller proportion of the microbiome. That proportion was even smaller in the baboons and rhesus macaques (both monkeys), who had a much larger number of types overall.
Council sums it up: “The microbiomes of our closest evolutionary relatives – the chimps – are similar to ours, but as you go farther back in evolutionary history, the microbiomes become much more complex.”
Evolution accounts for part of the difference: The skin microbiome evolves as its host does. However, the researchers think our modern lifestyle also plays a role. “We’re surrounded by a sterile environment,” Council said. “We no longer roll around in the soil. We put all these products on us that change the pH of our skin and change the environment for the microbes.”
Perhaps because different people use different products, there was more variability from human to human than in the other species. By far the most common bacteria in human armpits were species from the Staphylococcaceae family and the Corynebacterium genus. Study participants who regularly wore antiperspirant or deodorant tended to have more Staphylococcaceae than Corynebacterium; the reverse was true for people who wore neither.
Andrea Azcarate-Peril, the director of the Microbiome Core Facility at UNC-Chapel Hill and an assistant professor who studies the gut microbiome, calls the research “extremely interesting,” especially the finding that the human skin microbiome is less diverse than that of other primates. “It gives an idea of how far we have come from nature,” she said.
What are the implications of our less-diverse skin microbiome? Horvath and Council aim to explore this question next. “We now have the technology to look and see what these microbes have been doing for us and how they’ve been helping us and other primates for millions of years,” Council said.
The armpit research appeared in two scientific journals recently: Proceedings of the Royal Society B, in January, and the online open-access journal Peer J, in February.