Social Contact Helps Beneficial Gut Bacteria Spread

A study of chimp poop suggests that social animals share a collective microbiome that might help regulate health

Chimpanzees engage in social grooming in Gombe National Park. (Fiona Rogers/Corbis)
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When your co-worker is coughing up a storm, it's common sense to steer clear—we've known for over a century that social contact can aid the spread of pathogens that cause disease. Now, it appears the same rules may apply for helpful stomach dwellers, at least in sociable chimpanzees.

Gut microbiomes—the ecosystems of beneficial microbes inside animal bodies—seem to increase their diversity when their hosts are more gregarious, according to a study of chimpanzee poop conducted in Tanzania. This social spread creates a meta-community dubbed a pan-microbiome, which may function as a way to maintain diversity and avoid health problems that would arise if individual gut communities were more stable and were transferred only by heredity.

"You can think of the pan-microbiome as the Internet, which is full of information deposited by individuals,” says study co-author Howard Ochman of the University of Texas. "If one or more individuals lost this bit of information, it is possible to obtain it back.”

Ochman and his colleagues studied fecal samples collected from a group of chimpanzees in Gombe National Park. The samples came from 14 chimps observed as infants, juveniles, adolescents, adults and elderly apes over eight years. During that time, the chimps followed a typical pattern of seasonal social changes. They foraged together in larger groups during the wet seasons and dispersed into smaller groups or spent time alone during dry seasons.

Analysis of the fecal samples and the microbial information harbored within showed that while sociability wasn't associated with the abundance or absence of any specific bacterial types, it was linked to species diversity across the gut microbiome.

“The microbiomes of individual chimps contain more diversity during the more social wet season. We associated the social activity of the chimp population at large with microbial diversity within individuals,” says study leader Andrew Moeller of the University of California, Berkeley.

Babies get their initial gut microbe populations from their mothers, but the new data show that during their lifetimes, chimp hosts end up acquiring other types of gut bacteria through social interactions. In addition, the microbes move from gut to gut across generations and within the same generation, so their populations continually evolve within the community, creating a collective microbiome that itself evolves and is spread among individuals.

“If transmission were solely from mother to child, just by chance some microbes wouldn't make it, and they would be lost forever,” Moeller says. “In the social transmission scenario, this chance is greatly reduced, because now the microbes would have to be lost from every individual simultaneously, a very unlikely event.”

It's not entirely clear yet how the microbes make their way from chimp to chimp, Moeller notes. “It probably happens in many ways, including direct contact and exposure to feces.”

The study, published this week in Science Advances, corroborates previous work by Ran Blekhman of the University of Minnesota Twin Cities and his colleagues. That team showed strong associations between the amount of grooming contact between baboons and the compositions of their gut microbial communities.

While evidence of communal gut bacteria applies only to our primate relatives for now, there is a decent chance that human communities harbor their own pan-microbiomes. Exploring them may provide new clues to help our own health.

“A lot of people are interested in what actually changes or affects the microbiome, because we know those changes can impact our health,” says Blekhman. “We know that we get our first microbiome when we're born. But how does that change? What affects that change?”

For example, increased diversity of gut microbes could help fight ailments like Crohn's disease, which has previously been associated with changes in the human gut microbiome. But if useful weapons exist in a pan-microbiome, scientists must begin to take their measure before some species are lost forever, Moeller cautions.

“We know that westernization is disrupting our co-evolved native microbiota. So far, work has focused on the consequences of the loss of ancestral microbial diversity for individuals,” he says. “However, if bacteria are disappearing from the human pan-microbiome, they may never be recovered. It will be important in the future to catalog the microbial diversity of entire human populations, not just individuals.”

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