There may be more genes in the human microbiome than the universe has stars, finds a new report.
In the first study of its kind, Harvard Medical School researchers collected 3,500 microbio samples from both the mouth and the gut.
One estimate estimated the number of genes at 232 million, while another was comparable to the number of atoms in the universe & # 39 ;.
Surprisingly, half of the genes that researchers found seemed unique to an individual person.
The team says the findings may not only provide clues about environmental exposure or the risk of developing diseases, but may also lead to therapies that treat people based on their microbial genetic composition rather than the type of bacteria they have .
A new study from Harvard Medical School has shown that there can be anywhere from 232 million genes in the human microbiome up to a million trillion, the number of stars in the universe (file image)
The human microbiome – the collection of bacteria located in our nose, mouth, stomach and elsewhere – contains an estimated trillions of bacterial species.
Most are harmless, some even useful in improving immunity, fighting tumor growth, improving digestion and lowering cholesterol.
Others are harmful and cause plaque on the teeth, as well as skin and soft tissue infections.
Most previous studies have focused on identifying the different types of bacteria to learn how they affect our health.
& # 39; Our study is a gateway, the first step towards probably a long journey to understand how differences in gene content stimulate microbial behavior and affect disease risk, & # 39; said study lead author Braden Tierney, a graduate student at Harvard Medical School.
For the study, published in the journal Cell Host & Microbe, the team analyzed around 3,500 human microbiology samples.
About 1,400 were obtained from the mouths of the volunteers and 2,100 from the guts of the volunteers.
In total, the team found 46 million bacterial genes in the samples, about 24 million from the oral samples and 22 million from the intestinal samples.
Surprisingly, more than half of all genes found – about 23 million – were found only once, meaning that they were unique to an individual person.
Of this group, 11.8 million came from the mouth and 12.6 million from the intestine.
Even more interesting is that these unique have performed different functions than genes that are often shared.
While commonly shared genes help perform basic functions such as breaking down enzymes, unique genes are involved in more specialized functions such as antibiotic resistance.
& # 39; Some of these unique genes appear to be important in resolving evolutionary challenges, & # 39; Tierney said.
& # 39; If a microbe needs to become resistant to an antibiotic due to drug exposure or is suddenly confronted with a new selective pressure, the singleton genes may be the source of genetic diversity that the microbe can adapt to. & # 39;
Researchers don't know exactly why there is so much genetic diversity, but they think it resembles the ability of bacteria DNA to evolve rapidly, depending on environmental conditions and changes.
This includes the type of food that a person eats, any medication that he takes and even illnesses that someone might develop.
The estimates for the number of total genes ranged from 232 million to a number that was close to the number of atoms in the universe: 10 to the 78th power or ten trillion vigintillion.
According to another calculation, the number of genes is higher than the number of stars in the observable universe, which is a billion trillion.
But researchers say the actual number may never be known.
"Whatever it may be, we hope that our catalog, along with a searchable web application, will have many practical applications and generate many research directions in the field of host-microbe relationships," said co-senior author Dr. Chirag Patel, an assistant professor of biomedical informatics at the Blavatnik Institute of the Harvard Medical School.
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