Heat-tolerant creatures may benefit medicine
Vol. 17, No. 18Feb. 5, 1998

Heat-tolerant creatures may benefit medicine

In a steamy underwater hell west of Costa Rica, weird deep-sea worms survive temperatures nearly hot enough to boil water-too hot for any other complex creature on Earth-and they don't care if their 'heads' are two-and-a-half times cooler than their 'tails,' a UD researcher reported in today's issue of Nature.

The study, directed by Craig S. Cary, marine studies, is believed to be the first report of a "eukaryotic metazoan" or higher-order life form capable of surviving sustained, long-term exposure to temperatures up to 176 degrees Fahrenheit (80 degrees Celsius).

Camped on each Pompeii worm's back, hairy-looking bacterial hitchhikers crank out enzymes that may hold the key to new protein-based catalysts for making drugs, paper, food and a host of other goods, according to Cary, lead author of the Nature paper, with Tim Shank of the Institute of Marine and Coastal Sciences at Rutgers State University of New Jersey and Jeff Stein of Diversa Corp., San Diego.

"Because the Pompeii worm survives such a broad temperature gradient, so too must its bacterial partners," Cary said. "These bacteria may harbor unique eurythermal enzymes, capable of operating over a wide range of temperatures." In addition to their thermal versatility, he noted, eurythermal enzymes can be stored for longer periods of time, compared to conventional enzymes, and they can operate in organic solvents.

Cary's latest findings on Alvinella pompejana (the Pompeii worm) should boost the global search for new "extremophiles"-organisms tough enough to thrive in hot, corrosive, high-pressure environments. The applications for these organisms seem endless. Taq polymerase, for example, an extremophile enzyme discovered in hot springs at Yellowstone National Park, now allows researchers to amplify and analyze tiny bits of the genetic coding material, DNA (deoxyribonucleic acid). Heat-loving enzymes also help dislodge oil inside wells, convert cornstarch to sugar and support a host of other industrial processes by speeding biological and chemical reactions. Because doctors routinely prescribe enzymes such as the clot-buster, streptokinase, Cary said eurythermal enzymes may prove useful for pharmaceutical production, too.

Certain simple, "prokaryotic" organisms grow at temperatures above 235.4 degrees F (113°C), Cary said, but such high heat kills eukaryotes. "The nuclear and mitochondrial membranes in more complex organisms were thought to be their Achilles heel," he explained. "When those membranes melt, it's curtains for the eukaryote."

For most complex organisms, he added, "131 degrees Fahrenheit [55°C] has been the upper limit." The Sahara Desert ant, Cataglyphis, was long hailed as the most heat-hardy creature on Earth, capable of foraging for brief periods under a blazing midday sun, when temperatures soar to 131 degrees F. Then, French researchers reported spotting a Pompeii worm in water nearly twice as hot (221°F/105°C). But, Cary said, that exposure was fleeting, and the worm was outside its natural environment-the long, hot tubes it calls home.

To penetrate worm condos beneath the eastern Pacific Ocean, Cary's team used a specially designed device featuring a titanium probe that's six inches long but only three-quarters of a centimeter in diameter. Dubbed "the Mosquito," the probe was deployed by the deep-submergence vehicle Alvin during trips to the Axial Summit Caldera, west of Mexico and south of Baja, Calif.

At this site along the East Pacific Rise, the Earth's crustal plates are moving apart, creating hydrothermal vents and geysers that spew a hot, toxic brew of hydrogen sulfide and heavy metals into the sea. Here, the 4-inch-long Pompeii worm, covered with fuzzy bacteria, builds its home. Cary and his colleagues took Alvin close to worm tubes, and the pilot carefully manipulated the Mosquito into a Pompeii worm's 'front door'- an opening just 2 centimeters wide. At a depth of 6 centimeters inside the tube, the probe measured the temperature every 2 minutes, for up to three days. The team also measured the temperature at tube openings.

"The worm's gills, sticking out of the tube, are in water averaging 72 degrees Fahrenheit [22°C], while its posterior end is parked in water that's 176 degrees Fahrenheit [80°C]," Cary said. These readings, Cary said, are unprecedented. "No organism on the planet exists routinely for such a prolonged period of time in such an extreme thermal environment," he added.

How can the worms stand it? Clearly, Cary said, the tubes don't block much heat, and interior temperatures remain constant, so they're not being flushed by cooler water. In fact, water adjacent to the tube is much hotter, and therefore can't draw heat away from the worms. "It may be that these bacteria are insulating the worms in some way," Cary said. "We don't know yet if this is true, but our data shows that the bacteria thrive at high heat. If the bacteria can stand it, there's good reason to believe that their enzymes can, too."

-Ginger Pinholster
Photo by Robert Cohen