It is well known that people in different regions of the world differ in certain characteristics – this also includes properties of their intestinal flora. A genetic study is now revealing the background to this microbial diversity: the intestinal microbes have developed in parallel to the history of the spread of their hosts. It is also becoming clear that some of these organisms exhibit characteristics that reflect their strong dependence on the human gut environment. As the researchers emphasize, the study results have not only an evolutionary but also a medical significance: Microbiome therapies could be optimized for certain population groups.
We are changing habitats: in our intestines lives an illustrious community of microorganisms, which has become the focus of science in recent decades. It became increasingly clear what a complex role the intestinal microbiome plays in human health: physical and even mental problems can be traced back to a disruption in the partnership with the tiny creatures within us. In addition to the importance to health, scientists are also investigating how this system developed over the course of evolution. In principle, it is known that the intestinal microbiome can differ between populations and individuals: many microbial species are common, but certain strains differ significantly.
The international research team led by the Max Planck Institute for Biology in Tübingen has now investigated the assumption that certain types and strains of intestinal microbes accompanied groups of people as they spread across the world and produced certain characteristics in parallel with them. To investigate this possible co-diversification between gut bacteria and human populations, the scientists sequenced and analyzed thousands of bacterial genomes from a total of 1225 individuals from different parts of Europe, Asia and Africa. Based on certain genetic characteristics, they were able to draw conclusions about the developmental history of the microbes.
Historical link between microbes and humans
In the case of 59 microbial species, the researchers developed family trees in this way. They were then able to compare these with pedigrees of their human hosts, which they derived from genetic analyzes of their saliva samples. As they report, their analyzes revealed that over 60 percent of the microbial species examined show a parallel phylogenetic history with their human hosts. This means that these species evolved in the human gut over hundreds of thousands of years as humans spread across the Earth.
"It is also noteworthy that those strains that have followed our evolutionary history most closely are now most dependent on the gut environment," says senior author Ruth Ley from the Max Planck Institute for Biology. Based on the genetic information, it became clear that some of the microbial strains that developed together with humans are highly specialized for the living conditions in the human gut: they have comparatively small genomes and react sensitively to deviations in oxygen content and temperature. As a result, they hardly have a chance of surviving outside the human body. "The study results fundamentally change our view of the human intestinal microbiome," says Ley.
"Some of the intestinal microbes even behave as if they were part of the human genome," says lead author Taichi Suzuki from the Max Planck Institute for Biology: "These microbes are, so to speak, somewhere in the spectrum from 'free-living' to dependent on the human body environment. We were able to show that some human gut bacteria have come further along this spectrum towards irreversible dependency than previously thought.” In contrast, gut dwellers, which showed a weaker connection with human history, have significantly more characteristics of free-living bacteria, the report Scientist.
Microbiome therapies adapted to groups
Finally, they emphasize that the results could also have implications for the medical impact on human microbial communities. What is meant here are treatments for people with health problems that can be traced back to an unfavorable composition of their intestinal flora. You can benefit from the administration of so-called probiotics or from the transfer of "healthy" mixtures of intestinal microbes. Findings about the differences between the gut microbe strains of different population groups could be helpful because they may respond best to "their" microbes. "The microbiome is a therapeutic target for personalized medicine, and our results underscore the importance of a population-specific approach for microbiome-based therapies," the researchers write.
Source: Max Planck Institute for Biology Tübingen, specialist article: Science, doi: 10.1126/science.abm7759