Some intestinal bacteria have more than 15 million years – Sciences et Avenir

Some bacteria in our intestines back at least five million years, well before we became human, reveals research published in July 2016 in the journal Science . This finding suggests that evolution plays a greater role in the composition of the intestinal microbiota than previously thought, say the researchers.

This proves that there is an unbroken line of these bacteria for millions of years, since the emergence of the African apes “

these bacteria contribute to the early development of our intestines, cause our immune system to fight pathogens and could even affect our mood and behavior, they said. “We show with this research that some human intestinal bacteria directly descended from those who lived in the bowels of our common ancestors with monkeys” , says Andrew Moeller, a researcher from the University of California, Berkeley, a co-author. “This proves that there is an unbroken lineage of these bacteria for millions of years, since the emergence of the African apes “, he said.

Two separations for intestinal bacteria

So that humans and apes evolved into distinct species from ‘ a common ancestor, the bacteria present in the intestines of the latter have also evolved into different strains, these scientists have determined. They found genetic evidence that the separate evolution of these bacteria in different strains occurred when the common ancestors began to evolve into different species. And the first cleavage of intestinal bacteria occurred there are about 15.6 million years ago when the gorilla lineage diverged from that of other hominids (see diagram below). The second separation occurred there 5.3 million years when the human branch split from those of chimpanzees and bonobos. “We knew long ago that humans and our closest relatives, the great apes, have these bacteria in their intestines” reports Andrew Moeller. “The biggest question we set out to answer was whether where these bacteria, our environment or our evolution, and how long the lines persisted” , will add -he.

© Andrew Moeller

For this research, these scientists analyzed fecal samples from chimpanzees, bonobos and gorillas living in the wild in Africa and people in the United States. Fossil and genetic evidence has shown that these four hominid species have all evolved from a common ancestor who lived there more than ten million years. The researchers used genetic sequencing to analyze all the different versions of a bacterial gene present in all fecal samples. From these data, they were able to reconstruct the tree of evolution of the three groups of intestinal bacteria that make up more than 20% of the human microbiome. Two of these groups have a similar pattern to that of hominids.