You Are What Microbes You Eat
Japanese guts contain seaweed-scarfing bacteria, but North American guts don't, study finds
WEDNESDAY, April 7, 2010 (HealthDay News) -- The trillions of microbes in the human intestinal tract that help everything from digesting food to fending off pathogens may differ from culture to culture because of variations in diet, researchers now report.
The finding stems from a study of marine microbiology by researchers in France, who identified genes in a microbe found on decomposing seaweed that enables it to consume the seaweed. When they put genetic information into an international gene-sequencing database, they found that the gene is not only present in other marine species but in a microbe that resides in the guts of people in Japan.
Yet they could find no evidence that the microbe, Bacteroides plebeius, had ever been identified in the microbiota, or community of microorganisms, in the guts of people in North America.
"Gut microbiota are shaped by our nutrition, and what energy we take up from our nutrition is shaped by gut microbiota," said study co-author Mirjam Czjzek, a group leader in the marine plants and biomolecules department at the French National Center for Scientific Research. "This clearly is an important factor to be aware of for health."
At some unknown point in history, microbes that reside in the Japanese tract probably snatched up genes from seaweed passing through the large intestine, explained Justin Sonnenburg, assistant professor of microbiology and immunology at the Stanford University School of Medicine. Sonnenburg wrote an article accompanying the study, which is published in the April issue of Nature.
Those microbes then had an advantage over other microbes because they could digest seaweed, which helped them thrive, Sonnenburg said.
Having a microbe that is adept at digesting seaweed presumably makes the Japanese better able to extract calories from seaweed than Westerners, Czjzek said.
So does this mean sushi-loving Americans will soon acquire B. plebeius, too?
Probably not, the researchers said.
Today's food supply is far more sterile than the diets people were eating when this "lateral" gene transfer occurred, the experts said. Back then, people were probably eating seaweed that came directly from the ocean, with a higher microbe load than the nori sheets people eat today.
Overall, cleaner food and better hygiene is a good thing, responsible for dramatically reducing food-borne illness. But there might be some unintended consequences, including altering the microbiota in the intestines.
"The microbial load on the seaweed we currently eat is probably incredibly low," Sonnenburg said. "Gene transfer is probably less likely to occur in present day than it was 100 or 1,000 years ago. It's probably a very rare event."
Still, modern man isn't lacking for microbes. The human body is host to tens of trillions and possible hundreds of trillions of microbial cells -- more, in fact, than human cells. "Just by cell number, we are more microbial than we are human," Sonnenburg said.
The vast majority of the microbes are bacteria, although there are also smaller amounts of fungi and archaea, another type of single-celled organism. And most bacteria live inside the large bowel.
For the most part, it's a win-win relationship. The microbes have a safe habitat in which to grow and divide, and humans derive nutrients from the microbes and get help digesting food and fending off pathogens that can make them sick, Sonnenburg said.
"We have co-evolved with them, and they have become an integral part of our biology," he said."
Altering the microbiota can cause problems, Sonnenburg said. For instance, taking antibiotics, which knock down intestinal microbes in addition to killing harmful bugs, makes people more susceptible to salmonella, he added.
And he said that other research suggests that microbes may play a role in obesity, inflammatory bowel disease and immune system ailments.
The hyper-hygienic, highly caloric and processed foods most people in industrialized nations now eat amount to an experiment that is testing how rapidly the microbiota in the intestine can adapt, Sonnenburg said.
"We are conducting a huge experiment with an unknown outcome," he said. "Cleaning up the food we eat has had a very beneficial result in reducing food-borne disease. That can't be minimized. But there may be a cost associated with it."
The U.S. National Institutes of Health has more on human microbiota.