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Identical twins differ at gut level: intestinal microbes vary widely, perhaps influenced by diet.

Twins may share appearances, mannerisms, even clothes--but the microbes in their intestines are far from the same. By cataloging microbial genes in the gut, researchers have found that communities of bacteria can differ dramatically even between identical twins.

The findings, which appeared online April 2 in the Proceedings of the National Academy of Sciences, give scientists a deeper understanding of what makes one person's intestinal menagerie different from another's.

Working out what's behind the composition and function of a person's gut bacteria is "a very important problem," says microbiologist Frederic Bushman of the University of Pennsylvania School of Medicine in Philadelphia. Intestinal bacteria spur digestion, manufacture vitamins and keep people healthy; changes in the bugs have been linked to irritable bowel syndrome and metabolic disorders. Because of their role in processing the nutrients from food, gut bacteria may even influence body weight.

In the new study, researchers comprehensively sequenced bacterial genes in stool samples from a pair of identical twins, 26-year-old women from Missouri. Since identical twins have nearly identical DNA, any differences between their gut microbial populations would have to be due to nongenetic factors such as diet, disease history or exposure to antibiotics.

"Diet is probably a huge, huge factor," says study coauthor Jeffrey Gordon, a systems biologist at Washington University School of Medicine in St. Louis.

Only about 17 percent of DNA sequences in the twins' gut microbes overlapped, based on a classification scheme developed by the researchers. What's more, about 64 percent of the gene groups identified had not been seen in previous studies.

One of the notable differences between the twins was a gene group that produces proteins in a family called dockerins, which form assemblies that microbes use to break down cellulose. Only one twin's intestinal bacteria possessed these genes.

In addition to looking for which genes were present in the gut microbiomes, the team went a step further and determined which ones were active. Some microbial genes found in both twins showed similar levels of activity, but the researchers found differences, too.

"This is the first look at the repertoire of expressed genes," Gordon says. The results provide a baseline for understanding how gut microbe genes function differently in different people.

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Title Annotation:Body & Brain
Author:Sanders, Laura
Publication:Science News
Geographic Code:1USA
Date:Apr 24, 2010
Words:368
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