Modern City Dwellers Have Lost About Half Their Gut Microbes

Comparing genomes of intestinal bacteria in various primates and human populations begins to pinpoint the possibly helpful microbes that have gone missing from our guts. From a report: Deep in the human gut, myriad "good" bacteria and other microbes help us digest our food, as well as keep us healthy by affecting our immune, metabolic, and nervous systems. Some of these humble microbial assistants have been in our guts since before humans became human -- certain gut microbes are found in almost all primates, suggesting they first colonized a common ancestor. But humans have also lost many of these helpers found in other primates and may be losing even more as people around the world continue to flock to cities, a researcher reported last week at a microbiology meeting in Washington, D.C. Those absent gut microbes could affect human health, he says. "This work helps us develop a new understanding of the course of human biological and cultural development," says Lev Tsypin, a microbiology graduate student at the California Institute of Technology who was not involved in the new study. The microbiome comprises all the bacteria, fungi, viruses, and other microscopic life that inhabit an individual, be it a person, a plant, or a planaria. For humans and many other species, the best characterized microbiome centers on the bacteria in the gut. The more microbiologists study these gut microbes, the more they link the bacteria to functions of their hosts. In humans, for example, gut bacteria influence how the immune system responds to pathogens and allergens, or interact with the brain, affecting mood. Andrew Moeller, an evolutionary biologist at Cornell University, was one of the first to show that gut bacteria and humans have built these relationships over a very long time. Six years ago, he and colleagues reported the work showing human gut microbes are very similar to those in other primates, suggesting their intestinal presence predates the evolution of humans. But his follow-up studies, and work by others, also indicate the human gut microbiome has, in a general sense, become less diverse than the gut microbes in our current primate cousins. One study found 85 microbial genera, such as Bacteroides and Bifidobacterium, in the guts of wild apes, but just 55 in people in U.S. cities. Splitting the difference, people in less developed parts of the world have between 60 and 65 of those bacterial groups, an observation that ties the decrease in microbial diversity to urbanization.

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