Gut Bacteria That Put Brakes On Weight Gain In Mice

The researchers had known from previous work that a large group of about 100 bacteria was collectively able to prevent weight gain in mice, but finding a specific microbe that was key to weight maintenance was a laborious task. "The microbes that live in our gut don't like to live outside the gut at all," explains Kendra Klag, PhD, MD candidate at the Spencer Fox Eccles School of Medicine at the University of Utah and first author on the paper. Many are killed by the presence of oxygen and must be exclusively handled in airtight bubbles.

But after years of culturing individual microbes, Klag found that a rod-shaped bacterium called Turicibacter could single-handedly reduce blood sugar, levels of fat in the blood, and weight gain for mice on a high-fat diet.

"I didn't think one microbe would have such a dramatic effect-I thought it would be a mix of three or four," says June Round, PhD, professor of microbiology and immunology at U of U Health and senior author on the paper. "So when [Klag] brought me the first experiment with Turicibacter and the mice were staying really lean, I was like, 'This is so amazing.' It's pretty exciting when you see those types of results."

Turicibacter appears to promote metabolic health by producing fatty molecules that are absorbed by the small intestine. When the researchers added purified Turicibacter fats to a high-fat diet, they had the same weight-controlling effects as Turicibacter itself. They don't yet know which fatty molecules are the important part-the bacterium produces thousands of different fats, in what Klag describes as a "lipid soup"-but they hope to narrow down on the most important molecules in future work for potential therapeutic use.

The researchers say that Turicibacter's effects are unlikely to be unique; many different gut bacteria probably contribute to metabolic health. And results based in animal models may not apply to people. "We have improved weight gain in mice, but I have no idea if this is actually true in humans," Round says.

But they're hopeful that Turicibacter could provide a starting point for developing treatments that promote healthy metabolism and prevent excessive weight gain.

"Identifying what lipid is having this effect is going to be one of the most important future directions," Round says, "both from a scientific perspective because we want to understand how it works, and from a therapeutic standpoint. Perhaps we could use this bacterial lipid, which we know really doesn't have a lot of side effects because people have it in their guts, as a way to keep a healthy weight."

"With further investigation of individual microbes, we will be able to make microbes into medicine and find bacteria that are safe to create a consortium of different bugs that people with different diseases might be lacking," Klag says.