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Intestinal flora vary widely

13th April 2010

Diet and evolution cause people's intestinal bacteria to vary widely across the globe, according to a recent French study.

fishandsoybeans

Intestinal microbes or microbiota, which many probiotic drinks seek to generate, do everything from fending off viruses and bacteria to getting the most of the energy locked inside food.

Lacking microbiota may also be a risk factor for obesity, inflammatory bowel disease, and immune system ailments.

The researchers found that Japanese people's stomachs contain a microbe found on decomposing seaweed, a thing which is passed on genetically.

At some point during the prehistory of Japan, microbes in people's stomachs borrowed some of the genes from the seaweed they were digesting.

The trait was passed on through Japanese DNA to the rest of the island's inhabitants, and as a result, Japanese people can get many more calories from seaweed than people from other countries.

Justin Sonnenburg, assistant professor of microbiology and immunology at the Stanford University School of Medicine, said that the seaweed-eating microbes in Japanese people's DNA had an evolutionary advantage over other microbes.

However, people who eat sushi in modern times will probably not evolve a similar microbe.

The researchers said that 'lateral' gene transfer occurred more frequently when people ate seaweed that came directly from the ocean.

Sonnenberg said that the seaweed people eat on sushi today was much more sterile than ocean seaweed, and that gene transfer was something that could have occurred 100 or 1,000 years ago.

So, while a more sterile environment dramatically reduces foodborne illness, one of the unintended consequences of people's cleanliness could be that a poverty of microbiota slows the evolution of the human digestive tract, in addition to making us more susceptible to disease.

For the study, the researchers sequenced the genes of a microbe found on some decomposing seaweed, then searched an international gene-sequencing database for the same set of genes.

Study co-author Mirjam Czjzek, a group leader in the marine plants and biomolecules department at the French National Center for Scientific Research, said that gut microbiota were shaped by our nutrition, and by what energy we took up from our nutrition.

She said that stomach microbes were clearly an important public health issue. The human body may contain up to 100 trillion microbial cells.

Sonnenberg said that the number of microbial cells in the human body was definitely more than the number of cells that belonged specifically to the human body, and that humans had co-evolved with microbiota.

He said that people, as a whole, were more microbial than they were human.

Most of the human body's microbiota are bacteria living inside the large bowel, while others are fungi.

Archaea, another single-celled lifeform, make up a third class of the body's microbiota.

Sonnenberg said that the relationship between human beings and the microbiota that live inside their bodies was mutually benefical for both.

He said that human beings provided microbiota with a safe place to live, and that, in addition to causing food to decompose, the microbiota fended off viruses and bacteria so that people did not get sick.

 

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