A new study is the first to catalog the genetic variation of
microbes that lives in the gut, where they extract nutrients from food
synthesis vitamins, protect against infections, and produce compounds that are
naturally reduce inflammation. The widespread genetic diversity uncovered by
the scientists can help them understand how our microbial genes work together
with our human genes to keep us healthy or in some cases to cause disease.
The study, by researchers at Washington University School of
Medicine in St Louis and the European molecular Biology Laboratory in
Heidelberg, Germany, appears online in Nature. “Surprisingly, each of us can be identified by the
collective DNA of our gut microbes,” says corresponding author George Weinstock,
of Washington University.
“That collection is individualized, 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”
The researchers analysed the microbial DNA in 252 stool
samples from 207 individuals living in the United States and Europe. All the
subjects had participated in one of two recent high profile initiatives to
catalog the diverse species of microbes that live in and on the body. Neither
of those studies – the Human Microbiome Project and the Metagenomics of the
Human Intestinal Tract (MetaHIT) project- looked at the genetic variation of
the microbial genomes in the body.
For the new study, the 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.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
intestinal fluctuated.
“The microbial DNA in the intestine is remarkably stable,
like a fingerprint”, Weinstock explains. “Even after a year, we could still
distinguish individuals by the genetic signature of their microbial DNA.Babies become colonized with microbes as they pass through
the birth canal and into the world. Those microbes come from their mothers and
from the environment. Exactly how the microbes shape our lives is not yet
known, but in the gut research has suggested that an imbalance of bacteria may
contribute to irritable bowel syndrome, Crohn’s and obesity.
With this new catalog, the researchers can begin to understand
the selective forces that shape the microbiome-the collection of microbes and
their genes-in the intestine. “The DNA of our microbes is a historical record of the
microbial evolution in our bodies”, says co-author Makendonka Mitreva. “Many of these organism would have colonized us when we were
very young and would have grown and evolved with us throughout our lifetimes.”
The information gleaned from future studies of the gut
microbiome also may help scientists determine how the microbial genes can be manipulated
to improve human health and the effectiveness of certain medications, she adds.
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