April 13, 2006

Some worms like it really, really hot, study finds

By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) - A species of worm that thrives on
undersea hot-water vents prefers the hottest water possible,
choosing to live at temperatures that kill other animals,
researchers reported on Thursday.

Their unique abilities to withstand hot water shooting like
a geyser from hydrothermal openings may help the stalk-like
worms prey on bacteria that other animals cannot reach, the
researchers report in Friday's issue of the journal Science.

The tiny worms, known scientifically as Paralvinella
sulfincola, chose water heated to 122 F (50 degrees C) and made
brief forays into water as hot as 131 degrees F (55 degrees C),
Peter Girguis of Harvard University in Massachusetts and
Raymond Lee of Washington State University reported.

"To our knowledge, every other vent organism down there
dies at temperatures way below 50 and 55" Celsius, Girguis said
in a telephone interview.

The worms live on underwater vents found at depths of 1.4
miles off the Pacific coast of Washington. They are studied and
collected using submarines such as the deep-sea ALVIN
submersible, or robots.

They belong to a group known as polychaetes and build tubes
made out of mucus but can move around freely. They resemble
tiny red palm trees, with frond-like red gills.

Many different animals live on the deep undersea vents, not
merely tolerating the sulfur, heat and pressure but thriving in
it. They eat the bacteria that can live in much higher
temperatures than more complex animals.

The water pours out of the vents at temperatures far above
the boiling point but it quickly cools in the chilly sea water.
Because of the conditions, it is difficult to know precisely
which temperatures the animals can tolerate.


So Girguis and Lee set up a unique experiment.

"We wanted to see what temperatures the worms preferred and
what temperatures they could survive," Girguis said.

They built a special pressurized aquarium, with a heating
element on one end and a cooling element on the other.

This created a thermal gradient -- with water ranging in
temperature from 68 degrees F (20 degrees C) to 142 degrees F
(61 degrees C). They threw the worms in.

"What happened really kind of shocked us, which is they all
very quickly moved when we imposed the thermal gradient,"
Girguis said.

"They just picked up and went," he added. "It was like they
were having a little conference" in the hotter water.

The worms survived for as long as seven hours at 122
degrees F (50 degrees C), and would spend as long as 15 minutes
at 131 degrees F (55 degrees C). Water of 140 degrees F (60
degrees C) killed them.

These temperatures are far hotter than anything most
animals can survive. Other researchers have found desert fire
ants die at 131 degrees F (55 degrees C) and a hot tub, for
instance, ranges from 100 degrees F (38 degrees C) to 105
degrees F (40 degrees C).

Desert air is often hotter but water conducts heat much
more efficiently than air does.

Girguis said the experiment answered a key question about
the physiology of the worms.

The cells of complex animals all rely on structures called
mitochondria, which provide power to the cells. Mitochondria
start to break down at temperatures of 122 to 131 F (50 to 55
degrees C), Girguis said. The worms may skate on the
borderlines of this limit but do not break it.

They almost certainly have multiple other adaptations, he
said, including heat-tolerant enzymes in their cells.