The Early Worm Gets the Bacteria Infection.

The idea of having a bacterial infection of the skin makes most people queasy. But for the giant tubeworms living in inhospitable conditions near hydrothermal vents deep in the ocean, it's the only way to survive.

When the larvae of these tubeworms are born, they are bacteria free and have a full digestive system. They can swim and eat like most other youth. But as they age and settle in the bottom of the ocean near a volcanic vent their mouths disappear and their stomachs shrinks away.

Before this happens, sulfur-eating bacteria infect the larvae through their skin. By the time the tubeworm settles down they have grown an organ, the trophosome, to house the symbiotic bacteria and they rely completely on the bacteria to metabolize the sulfurous liquid around them for nutrition.

"It is an absolutely obligate symbiosis for the worm," said Charles Fisher, professor of biology at Penn State. "If the larvae do not get the right symbiont, they die."

The researchers found that once the bacteria get into the larvae, further infection is prevented.

"The symbiont, and only the symbiont, is capable of invading the skin of the tubeworm larvae," said Monika Bright of the University of Vienna. "It migrates through several layers of tissue towards the interior of the host, and into the future trophosome. Once the trophosome is established, infection ceases, and no further infection appears to be possible at later stages."

--Sara Goudarzi

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Credit: Andrea D. Nussbaumer, Charles R. Fisher and Monika Bright