David
Perlman
Chronicle Science Editor
Special
organisms adapt to super-hot environments Scientists
are exploring a strange new world of mountain ranges deep beneath the oceans,
where erupting volcanoes harbor astounding varieties of life forms never seen
before -- microbes in varied species by the thousands and animal species in the
hundreds.
In those "biodiversity hot spots," as one researcher calls them,
the scientists see fresh clues to the workings of evolution, perhaps to the origins
of earthly life, and even a future of practical progress in quests for new drugs.
Called deep-sea hydrothermal vents, those volcanoes were discovered barely
25 ago, and by now more than 100 such vents have been at least partially explored.
No one knows how many more there are, nor what they will reveal in countless unknown
species of marine creatures.
Yesterday, at the annual meeting of the American
Association for the Advancement of Science in San Francisco, a group of researchers
in biology, genetics and chemistry described their most recent explorations and
what they have found in what is still an infant science.
At each vent
along 25,000 miles of mid-ocean ridges in the Atlantic and the Pacific, the erupting
volcanoes swiftly build tall rock chimneys whose throats spew sea water heated
to 700 degrees or more -- twice the temperature at which a chicken bakes.
Around
those chimneys, sulfur-eating microbes combine only with oxygen and carbon dioxide
to feed far larger creatures like red-tipped tube worms that have neither mouth
nor gut nor anus but live entirely on colonies of the microbes that dwell inside
them. Tiny shrimp, mussels and clams feed on huge clouds of microbial cells that
swirl around the hot basalt chimneys like wisps of fog around the summit of Twin
Peaks.
Many of those microbes are not bacteria at all, but belong to the
most primitive of all life forms -- a new class known as archaea, that were discovered
at a hydrothermal vent site by scientists aboard a deep-sea submergence vehicle
called Alvin off the coast of Baja California in 1982. They may well be descendants
of the first living things to emerge on Earth nearly 4 billion years ago, said
Cindy Lee Van Dover of the College of William and Mary in Williamsburg, Va.
"We
really don't know yet what's growing inside those chimneys," said Van Dover, who
is the only woman ever to pilot the deep submersible Alvin on dives to the hydrothermal
vents. She is leading an expedition to an unexplored vent in the Indian Ocean
this spring, after having dived to volcanic vents on both the mid-Atlantic Ridge
and along the East Pacific Rise off the coast of Mexico.
Each vent site
Van Dover has explored is like a separate island, and her colleagues have found
distinctive creatures on each that have emerged there alone, offering an evolutionary
puzzle much like species on earth that diverge with isolation and alter their
forms to cope with differing environments. "They are truly microbial gardens,"
she said.
Hydrothermal vents are created when two huge slabs of the earth's
crust, known as tectonic plates, split apart in the mid-ocean and molten magma
from beneath the crust wells up onto the sea floor. Given a few million years,
those vents and chimneys of volcanic basalt become mountain ridges thousands of
miles long.
Marine Biologist Stephen Craig Cary of the University of Delaware
has collected many species of heat-loving microbes, and at least one worm around
a smoking volcanic chimney that is truly unique. It thrives where the water temperature
is at least 183 degrees -- "the most heat tolerant of any organism, " Cary said.
A tiny creature less than than three inches long, Cary's "Pompeii worm"
looks like a fuzzy caterpillar, but its coat of fuzz is actually a colony of four
varied and slimy species of thin rod-shaped bacteria. Sea water flushes through
the heads of the Pompeii worms at 57 degrees -- cold enough for swimmers to shun
Lake Tahoe or San Francisco Bay -- and through their tails at 222 degrees, 10
degrees above boiling water, Cary found. "We don't know how they do this," he
said in wonderment.
Cary also analyzes the genes that confer such remarkable
heat tolerance on the Pompeii worm, and on other heat-loving organisms around
hydrothermal vents as well. He finds that their bodies possess unique sets of
heat-tolerant enzymes that make them extremely interesting to pharmaceutical companies
seeking to develop new drugs that can exploit high temperatures. Soary's laboratory
is already working with one firm that sees a profitable potential in deciphering
the worm's unique genome, he said. |
