Earth's Hottest "Bods" May Belong to Worms

John Roach
for National Geographic News
December 8, 2004
Perhaps the most heat-tolerant complex organisms on Earth, Pompeii worms (Alvinella pompejana) thrive along hydrothermal vents found deep in the Pacific Ocean.

Wrapped in fleecelike mantles of bacteria, the worms live in papery tubes, which they burrow into the sides of deep-sea geysers. The hydrothermal vents spew a toxic brew of boiling water, sulfur, and metal compounds.

Scientists say the water temperature at the base of the tubes is 176 degrees Fahrenheit (80 degrees Celsius). Only single-celled bacteria are known to survive hotter temperatures.

"How the worm tolerates these temperatures is still unknown," said Craig Cary, a marine biologist at the University of Delaware in Lewes, who is leading his sixth trip to the East Pacific Rise, an underwater volcanic mountain chain about 1,200 miles (2,000 kilometers) west of Costa Rica, to study the creatures.

Pompeii Worm

A team of French scientists first discovered the Pompeii worm at hydrothermal vents in the Galapagos Islands in the early 1980s.

Since then, scientists have labored to understand how the four-inch-long (ten-centimeter-long) worms thrive in their extreme environment.

Not only do they survive the scalding temperatures and toxic chemicals spewed by hydrothermal vents, but the worms also live in total darkness and under the crushing pressure of the deep ocean.

In 1998 Cary and colleagues published findings on the temperature of the Pompeii worm's tube in the science journal Nature.

Water at the tube bottom is a scalding 176 degrees Fahrenheit (80 degrees Celsius), while the worm's head, which sticks out of the tube, rests in water at a tepid 72 degrees Fahrenheit (22 degrees Celsius).

Prior to the discovery, few, if any, scientists believed complex organisms could survive such extreme environmental temperatures, Cary noted. He cautioned, however, that he and his colleagues only measured the temperature inside the tube, not the worm itself.

The finding raises the question of how the worm survives such extreme heat.

James Childress, a marine biologist at the University of California, Santa Barbara, has extensively studied hydrothermal vent systems. He said, "I believe the Pompeii worm probably survives by avoiding the very high temperatures [that] are found in its environment."

The worms are covered in a hairy, gray fleece composed of bacteria. The bacteria feed on mucus secreted by glands on the worms' backs. Cary said the fleece may function for the worms like a firefighter's heat blanket.

"Maybe the worm uses the fleece to help shield it from the intermittent blasts of hot water that it experiences in the tube. Or maybe they feed directly on their crop [of bacteria]," he said. "Right now, we really do not know. But the environment is so harsh that it is probable that [the bacteria] help the worm cope."

The bacteria have long been the main interest of Cary and his research colleagues. The scientists believe the organisms may harbor enzymes useful for cleaning up oil wells, processing new drugs, and speeding up chemical reactions used in industry.

"Metagenomic" Survey

To understand how the bacteria and the Pompeii worm work together to function in this extreme environment, Cary and his colleagues are conducting what they call a metagenomic survey of the microbial community.

"Basically, we decided that rather than try to look at each member of the community individually, we would look at all of them at once using the same genomic tools used to look at the human genome," Cary said.

The Human Genome Project was an international research effort completed in 2003 to map and sequence all the human genes.

Cary and his colleagues are sequencing the DNA from the bacterial community on the Pompeii worm's back and using a computer program to generate an image of the genes the community as a whole uses to survive.

The scientists hope to then construct an array of these genes and test them at the hydrothermal vent environment.

"Our hope is that through these analyses we will be able to answer many questions about the bacteria, the worm, and their environment," Cary said.

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