When the first humans left Africa, they brought their gut microbes with them. Turns out, these microbes co-evolved with it, too.
The The human gut microbiome It consists of hundreds of thousands of species of bacteria and antique. Within a particular type of microbe, different strains carry different genes that can Affect your health and the diseases you are susceptible to.
there The obvious difference In the microbial composition The gut microbiome varies among people who live in different countries around the world. Although researchers are beginning to understand the factors that influence microbiome composition, such as diet, there is still limited understanding of why different strains of different groups of the same type of microbe exist in their guts.
We are researchers studying bacterial evolution And the microbiome. our A recently published study They discovered that not only did microbes diversify with their first modern human hosts as they traveled around the world, they followed human evolution By restricting themselves to life in the gut.
Microbes share an evolutionary history with humans
We hypothesized that as humans spread across the globe and diversified genetically, so did the microbial species in their guts. In other words, the gut microbiome and its human hosts “formed” and evolved together—just as humans diversified so that people in Asia look different from people in Europe, so did their own microbiomes.
To evaluate this, we needed to pair human genes and microbiome data from people around the world. However, the data sets that presented both Microbiome data The genome information of the individuals was limited when we started this study. Most of the publicly available data was from North America and Western Europe, and we needed more representative data for worldwide populations.
So our research team used existing data from Cameroon, South Korea, and the United Kingdom, as well as recruiting mothers and their young children in Gabon, Vietnam and Germany. We collected saliva samples from adults to ascertain genetic makeup or characteristics, and stool samples for the genome sequence of their gut microbes.
For our analysis, we used data from 839 adults and 386 children. To assess the evolutionary history of humans and the gut microbiome, we created phylogenetic trees per person plus 59 strains of the most common microbial species.
When we compared human trees to microbial trees, we discovered a gradation of their compatibility. Some bacterial trees did not match human trees at all, while some matched well, indicating that these species are well organized with humans. In fact, some microbial species have been along the evolutionary path for over hundreds of thousands of years.
We also found that microbes that evolved alongside humans had a unique set of genes and traits compared to microbes that were not coded with humans. Microbes that have partnered with humans have smaller genomes and greater sensitivity to oxygen and temperature, most of which are unable to tolerate conditions below human body temperature.
In contrast, gut microbes with weaker links to human evolution possess traits and genes characteristic of free-living bacteria in the external environment. This finding suggests that co-diversified microbes are highly dependent on the environmental conditions of the human body and must be transmitted rapidly from one person to another, either across generations or between people living in the same communities.
Confirming this mode of transmission, we found that mothers and their babies had the same strains of microbes in their guts. By contrast, microbes that were not encoded were more likely to survive well outside the body and could be transmitted more widely through water and soil.
Gut Microbiome and Personalized Medicine
Our finding that gut microbes evolved alongside their human hosts provides another way to view The human gut microbiome. Gut microbes have passed between humans over hundreds to thousands of generations, like this As humans change, so have their gut microbes. As a result, some gut microbes behave as if they are part of the human genome: they are bundles of genes passed down between generations and shared by related individuals.
personal medicine Genetic testing is beginning to make treatments more specific and effective for the individual. Knowing which microbes have forged long-term partnerships with people may help researchers develop microbiome-based therapies that are specific to each population. Doctors are already using Probiotics from local sources Derived from the gut microbiome of community members to treat malnutrition.
Our findings also help scientists better understand how microbes transition ecologically and evolutionarily from “free-living” in the environment to being dependent on human gut conditions. Diverse microbes have traits and genes Remember the bacterial symbionts that live inside insect hosts. These common features suggest that other animal hosts may also have gut microbiome that ranked with them on the evolution.
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