Scientists have started to catalog the genes of all human microbiomes. For now, by studying the bacteria and viruses of the intestine and mouth of 3,655 people, they counted no less than 45 67 million different genes, half of which are unique to each individual.
After the Human Genome Project, the Universe of Microbial Genes. Launched in 1990 and completed in 2003, the first has made it possible to sequence the entire human genome. While 100,000 human genes were estimated to be genetic information, this large-scale program determined that our genome actually contains between 20,000 and 25,000 genes encoding proteins. Today, American scientists are attacking Universe of Microbial Genes, an equally ambitious project, if not more: they began cataloging the genes of all human microbiomes. In an article published August 14 in the journal Cell Host & Microbe, they unveiled their first results. Every human being has his own bacterial identity!
By studying the bacteria and viruses of the intestine and mouth of 3,655 people, researchers at Harvard University and Joslin Diabetes Center in Boston counted as many as 45 67 million different genes. More interesting: half of them are unique to each individual (11.8 million genes of the oral microbiome and 12.6 million intestinal microbiome), they explain in the study. Thus, on a global scale, the number of genes of all human microbiomes could be greater than the number of stars in the visible Universe, they argue.
It is estimated that the bacterial communities in the intestine, skin or lungs of a human are ten times more numerous than the cells of the body. Moreover, "two bacteria of the same strain may have genetic differences," explain the researchers.
An adaptive evolution of bacteria?
While they thought these mutations came from horizontal gene transfers, they found in their study that less than 2% of the unique genes detected in individuals came from this process. They therefore rather consider an adaptive evolution. Thus, when we change our diet or take this or other treatment, the bacteria in our microbiome modify their DNA to adapt to the modification of our environment. "It's because of this genetic diversity that a microbe becomes, for example, resistant to an antibiotic," says Braden Tierney, a biologist at Boston's Joslin Diabetes Center and lead author of the study.
"Overall, these results provide potential bases for the unexplained heterogeneity observed in human phenotypes derived from microorganisms," the researchers conclude.
Thus, this company is revolutionary in the sense that it shows that studies on the microbiota must be rethought to take into account the heterogeneity of genes. Now, determining the type of microbial strain to know its effects is not enough anymore. From now on, it will also be necessary to study its genetic inheritance, specific to each one, explain the researchers. The ultimate goal is to be able to offer tailored treatments to each patient.
The intestinal microbiota more and more studied
For some time, scientists have become increasingly interested in the microbiome. Many studies have been conducted on the gut microbiota or microbial flora. Composed of a multitude of microorganisms located in the digestive tract, it has about 100,000 billion bacteria whose very balanced organization contributes to the proper functioning of the digestive system and the immune system.
Thus, in recent years, these bacteria have helped to better understand certain diseases such as diabetes, obesity, Crohn's or fibromyalgia.
In 2014, in collaboration with an international team, French researchers managed to analyze all the genes of these bacteria. By studying 396 stool specimens, they identified 741 bacterial species, 85% of which were previously unknown. From their paper in the magazine Nature Biotechnologyscientists were able to reconstruct the complete genome of 238 bacteria, without prior culture.