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Two Harvard Biologists Find Animal With Bacteria-Free Gut

By Jennifer H. Arlen

Two Harvard biologists have found a genus of marine animals which has no bacteria in its digestive tract.

Paul J. Boyle, a graduate student in the Faculty, and Ralph Mitchell, professor of Applied Micro-Biology, discovered the phenomenon in Mitchell's laboratory at the Harvard Laboratory of Microbiological Ecology.

Boyle said he knows of no other animals that have a bacteria-free gut as a normal condition.

Couldn't Be

Boyle and Mitchell thought they had made a mistake when they originally discovered the phenomenon last summer. They were convinced all animals have micro-organisms in their digestive tracts, Boyle said.

"Essentially what we know is that the animal ingests bacteria and has no bacteria in its gut, so it must have a system for killing bacteria", Boyle added.


The animals are small marine wood-borer isopod crustaceans called Limnoria spp. There is one species of terrestial wood-borer crustaceans which also has a bacteria-free digestive tract.

The animals, sometimes called gribbles, produce a chemical that kills bacteria more powerfully than any other animal-made substance. They use the chemical to destroy all the microorganisms in the wood they eat.

The animals cause a fair amount of damage to wood in coastal zones, Boyle said.

"If we understand how the animal keeps its gut bacteria-free we may be able to interrupt that system and make the animal sick," he said, adding, "It might give us the ability to control its wood-boring activities."

They are studying the interactions between micro-organisms and marine invertebrates in order to find non-toxic means to control marine organisms which damage boats and docks, Boyle said.

Gut Feeling

The animal may have important implications for the Medical area because researchers need animals with bacteria-free guts in order to study colonization of digestive tracts by micro-organisms.

Mitchell and Boyle submitted a paper to the journal "Science," which will be published in June.

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