The threat of industrial life to ancient human gut bacteria

The results of the new research showed that some human intestinal bacteria have been passed from one generation to another for thousands of years, but many of these microbes have now become rare or extinct in the population of industrialized countries.

According to Ambassador Arjan's report, citing Ambassador Arjan, some types of bacteria that live in human intestines have probably been with our ancestors for tens of thousands of years, and it seems that humans have transferred these microbes from one generation to another by migrating to different parts of the world and forming families. The results of the new research have identified signs of this common history in two indigenous communities that lived at a great geographical distance from each other. These tribes are the "Simane" tribe in the Bolivian Amazon region and the "Hadza" tribe in northern Tanzania.

Despite this geographical distance, both groups share many common bacterial species in their gut. It is possible that the ancestors of these two communities carried these bacterial species long before their descendants lived on separate continents.

Today, many of these bacteria are rarely found in the bodies of people in industrialized countries or have completely disappeared, so scientists wanted to know what microbes have disappeared and whether this has affected human health or not.

The intestine is home to a collection of very small living organisms, including bacteria. Together, these microbes form a group that scientists call the "gut microbiome". Food and contact with others help form this complex, but some of its members may be much older than a human's lifespan.

Stanford microbiologist Justin Sonenberg and his colleagues compared the two communities to investigate this possibility. "Simane" people engage in agriculture, fishing and collecting natural foods, and "Hadza" people make their living mainly through hunting and food gathering. Examining these communities can help identify bacteria that lived in the human gut in the distant past.

The researchers collected 133 stool samples from 85 people from the Simane tribe and analyzed the microbial DNA in these samples to identify the microbes living in the intestines. Using this DNA, the research group reconstructed a total of 12,746 microbial genomes.

Then the researchers compared this information with the previous data of 137 people from the "Hadza" tribe. Among the 1408 microbial species identified in the samples of the "Simane" tribe, 1231 species were also present in the samples of the "Hadza" tribe. This finding means that the "Hadza" people have almost most of the bacterial species found in the intestines of the "Simane" people in their bodies. However, 848 of these common variants are found rarely or not at all in populations of industrialized countries.

Identifying the same species in both societies was the first stage of research. The researchers had to determine how these microbes entered the body of the two groups. Another possibility was that the bacteria remained in the body of their ancestors for thousands of years and were passed from one generation to another. To distinguish between these two possibilities, the researchers looked at different species of each bacterium, called "strains."

The researchers examined 636 bacterial species for which sufficient "DNA" information was available from both populations and found no evidence of exchange of strains between the two populations in relatively recent times. So, even though both groups had the same bacterial species, they usually had different versions of these bacteria living in their bodies.

To estimate how long it took the two sets of bacterial strains to separate, the researchers looked at DNA that the bacteria had exchanged with each other in the past. After such an exchange, both strains had the same long section of genetic instructions, but this same section did not remain intact forever, and new genetic changes gradually divided it into smaller pieces. Therefore, the length of the remaining section can act as a kind of approximate clock to estimate when the genetic exchange took place. These findings suggest that gut bacteria continue to move between industrialized populations.

This pattern did not apply to all species. Three bacterial species showed signs of more recent exchange of strains between the two communities of "Simaneh" and "Hadza". These three species include Escherichia coli, Akkermansia muciniphila and Bacteroides ovatus. All three species are also widely found in industrialized populations. The researchers examined another 8,855 microbial genomes from Europe, Asia and North America and found close relatives of these strains in these regions as well.

They believe that contact with people outside these communities probably caused these strains to enter both groups. The history of some other bacteria was different. These bacteria lived in the guts of humans all over the world, but the strains in the two communities, "Simane" and "Hadza", still showed their ancient separation. Therefore, the geographical spread of a species does not only mean that the species has been dispersed in different areas in recent periods.

The researchers coined the term "VANISH" for a group of microbes that are still common in non-industrialized populations but rarely found in industrialized populations. Many common species between the two communities "Simaneh" and "Hadza" belong to this group. The findings of the research show that the distant ancestors of these two communities probably carried many of these bacteria. If this hypothesis is correct, people in industrialized countries may have lost microbes that have lived alongside humans for thousands of generations and been passed down from generation to generation.

The answer to this question is not clear yet. This research has examined the "DNA" of microbes, and in it, the health of people who have these bacteria in their bodies has not been tested. Researchers have pointed to previous evidence that suggests a link between the loss of VANISH microbes and some chronic disorders.

However, the existence of a relationship between two factors does not mean to prove a cause and effect relationship. The results of this research cannot show that the loss of these bacteria causes disease or that returning them to the body can improve people's health.

According to the report of the site Erth, the time estimates of this research also have limitations because they depend on the estimation of the rate of change of the "DNA" of the bacteria. Therefore, the dates provided are valuable clues but not completely accurate answers. Any attempt to bring these microbes back into the human body requires more research and the participation of indigenous communities that still have these bacteria in their bodies.

The results of this research have been published in the scientific journal Nature.

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