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Archive - Aug 19, 2013 - Story

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Mechanism Determined for How Beneficial Bacteria Persist and Thrive in GI Tract

The human body is full of tiny microorganisms—hundreds to thousands of species of bacteria collectively called the microbiome, which are believed to contribute to a healthy existence. The gastrointestinal (GI) tract—and the colon in particular—is home to the largest concentration and highest diversity of bacterial species. But how do these organisms persist and thrive in a system that is constantly in flux due to foods and fluids moving through it? A team led by California Institute of Technology (Caltech) biologist Dr. Sarkis Mazmanian believes it has found the answer, at least in one common group of bacteria: i.e., a set of genes that promotes stable microbial colonization of the gut. A study describing the researchers' findings was published as an advance online publication of the journal Nature on August 18, 2013. "By understanding how these microbes colonize, we may someday be able to devise ways to correct for abnormal changes in bacterial communities—changes that are thought to be connected to disorders like obesity, inflammatory bowel disease, and autism," says Dr. Mazmanian, a professor of biology at Caltech whose work explores the link between human gut bacteria and health. The researchers began their study by running a series of experiments to introduce a genus of microbes called Bacteriodesto into sterile, or germ-free, mice. Bacteriodes, a group of bacteria that has several dozen species, was chosen because it is one of the most abundant genuses in the human microbiome, it can be cultured in the lab (unlike most gut bacteria), and it can be genetically modified to introduce specific mutations. "Bacteriodes are the only genus in the microbiome that fit these three criteria," Dr. Mazmanian says. Lead author Dr. S. Melanie Lee, who was an M.D./Ph.D. student in Dr.