"Surprisingly, each of us can be identified by the collective DNA of our gut microbes," said researcher George Weinstock, associate director of The Genome Institute at Washington University.
"That collection is individualised, completely analogous to our human genome. Differences in the way individuals respond to various drugs or the way they use specific nutrients can be traced to the genetic variation in our microbial genes as well as in our human genes," Weinstock said.
The study, by researchers at Washington University School of Medicine in St Louis and the European Molecular Biology Laboratory in Heidelberg, Germany, is the first to catalog the genetic variation of microbes that live in the gut.
The study sheds light on how gut microbes extract nutrients from food, synthesise vitamins, protect against infections, and produce compounds that naturally reduce inflammation.
The researchers analysed the microbial Deoxyribonucleic acid (DNA) in 252 stool samples from 207 individuals living in the United States and Europe.
Researchers zeroed in on 101 species of microbes commonly found in the intestine, identifying more than 10 million single-letter changes in the collective DNA of those microbes.
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They also found numerous other DNA alterations, including insertions, deletions and structural changes.
In 43 subjects for whom the researchers had two stool samples collected at least a month apart (most were collected six months to a year after the initial sample), the researchers found very little variability in the microbial DNA over time, although the species of microbes in the intestine fluctuated.
"The microbial DNA in the intestine is remarkably stable, like a fingerprint. Even after a year, we could still distinguish individuals by the genetic signature of their microbial DNA," Weinstock said.
"The DNA of our microbes is a historical record of the microbial evolution in our bodies," said co-author Makendonka Mitreva, assistant professor of medicine in a statement.
"Many of these organisms would have colonised us when we were very young and would have grown and evolved with us throughout our lifetimes," Mitreva said.
The study was published in journal Nature.