Gut and human microbes on a joint evolutionary journey

Sep. 16 () –

Gut microbes share a parallel evolutionary history with their human hosts: they co-evolved in the gut environment of our species for hundreds of thousands of years.

Furthermore, some microbes exhibit genomic and functional characteristics that make them dependent on their host, a new study by scientists at the Max Planck Institute for Biology in Tübingen reveals. published in Science and carried out with data from 1,225 people from Africa, Asia and Europe.

Many species of microbes in the human gut can be found in populations around the world. However, within a species of microbe, microbial strains vary markedly between individuals and populations. Despite their importance to human health, until now little was known about the origins of these strains. Furthermore, most of these strains live almost exclusively in the human intestine. This raises the question of where the microorganisms in the human intestine come from.

The research team surmised which specific species and strains have been with people as humanity diversified and spread across the globe. To test whether microbes evolved and diversified simultaneously with their human hosts, researchers from the Max Planck Institute for Biology, the Institute for Tropical Medicine and the IMFC Group of Excellence at the University of Tübingen systematically compared the evolutionary histories of humans for the first time. . and intestinal microbes.

The researchers created phylogenetic trees for 1,225 human study participants, as well as for 59 microbial species found within their intestines, and used statistical tests to investigate how well these trees matched. More than 60% of the investigated species matched the evolutionary history of their human host, meaning these microbes co-diversified over about 100,000 years in the human gut when people moved out of Africa across the continents.

“We didn’t know that any of our gut microbes followed our evolutionary history so closely,” he says. it’s a statement Ruth Ley, head of the Microbiome Sciences department at the Max Planck Institute for Biology, Tübingen, where the study was conducted, and deputy spokesperson for the IMFC.

“It is also notable that the strains that most closely followed our history are now the most dependent on the gut environment.“, adds Ley. In fact, some of the strains of microbes that co-evolved with humans are highly dependent on the human gut environment: they have smaller genomes and are more sensitive to oxygen levels and temperature, traits that make it difficult to survival outside the human body In contrast, microorganisms that showed a weaker association with human history showed characteristics more similar to free-living bacteria.

“Some of the gut microbes behave as if they were part of the human genome,” explains Taichi Suzuki, who shares the main authorship of the study with his colleague Liam Fitzstevens. “Those microbes can be imagined to be on a gradient from ‘free-living’ to dependent on the human body environment. We have seen that some human gut bacteria are further along the gradient toward irreversible host dependence than previously thought.”

Law says: “This fundamentally changes the way we view the human gut microbiome.”

To obtain data from a diverse subset of the world’s population, the research team analyzed the gut microbes and genomes of 1,225 people in Europe, Asia and Africa. The stool and saliva samples were collected with the help of researchers from the Institute of Tropical Medicine at the University of Tübingen and its partners in Vietnam and Gabon. Additionally, researchers from around the world supported the study by providing similar data sets from participants recruited from Cameroon, South Korea, and the United Kingdom.

The study findings help to better understand population-specific microbes that have long been associated with the local human population. With this knowledge, microbiome-based disease therapies can be tailored and refined for population-specific treatment.