US Studies Show Germs Help Species Evolve

WASHINGTON - The germs that help cattle eat grass and gorillas gorge on leaves may have been the secret weapon that let mammals populate the planet, researchers reported on Thursday.

Two separate teams of researchers reported on the bacteria living in and on the bodies of humans and other animals, and found they are surprisingly well-adapted to their hosts -- so well that they may have helped different species evolve.

"We have evolved together with our bacteria," Dr. Julie Segre of the National Human Genome Research Institute said in a telephone interview.

Both teams looked at the DNA of the bacteria, as opposed to trying to painstakingly grow them in lab dishes. They said this method helped them find species missed by older techniques.

Not only have the microbes evolved with us, but perhaps animals that have made good use of bacteria have been able to evolve further, one team of US researchers said.

In another study, Segre's team found more than 130 different species living on the skin, many that no one knew were there before.

"I thought it was amazing that there were a million bacteria per square centimeter. The bacterial cells outnumber us," said Segre, whose study is published in the journal Genome Research.

Jeffrey Gordon of Washington University in St. Louis and colleagues looked at the droppings of 60 different species of mammals and found meat-eaters, plant-eaters and omnivores such as humans each have their own unique set of gut bacteria.

Writing in the journal Science, they said the ability of mammals to acquire new symbiotic bacteria in their digestive systems may have helped so many different species evolve.

"This could account for the spectacular success of mammals and herbivores in particular," they wrote.

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Animals, and especially mammals, make use of bacteria to help digest their food. Gordon's team found that herbivores had the most diverse species of bacteria in their faeces -- a not surprising finding given that the bugs are needed to break down the tough cellulose found in grasses and other plants.

Carnivores had the fewest number of different species and omnivores fell in the middle. Human poop bacteria looked much like that of other omnivores, they said.

Members of the same species living in the wild and in zoos had similar gut bacteria. And a strict vegetarian human had similar bacterial residents to the meat-eating people.

A team at The Institute for Genomic Research in Maryland found in 2006 found that the number of bacteria in the human gut outnumber the cells in our bodies, and proposed that many be classified as true symbionts with Homo sapiens.

Segre's team took samples from the insides of the elbows -- a place known to be prone to eczema, a flaking skin disorder. Psoriasis, another skin disease, is found on the outside of the elbow and she believes bacterial and fungal populations may play a role.

Learning how to manipulate bacteria may hold the secret to treating these diseases, Segre said. Bacteria that break down the sebaceous output of tiny skin glands help turn the waxy substance into natural moisturizer and learning more about how they do this could form the basis of an entire new beauty industry.

"I think we do really need to change the language about thinking about bacteria as pathogenic," Segre said. "We should appreciate bacteria as helping our health."

(Editing by Cynthia Osterman)

Story by Maggie Fox

Story Date: 23/5/2008

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