The walls are alive

Deep in a cave, scientists glimpse a strange new biology

BY CHARLES PETIT

For centuries and perhaps millenniums, a sulfurous cave near the small town of Tapijulapa in southern Mexico's state of Tabasco has been regarded by locals as the home of powerful spirits. Fertility rituals are still conducted there, the largely Mayan people feasting on tiny fish that thrive in milky-white waters flowing through the cavern's passages and out its entry.

Now it appears that the folklore is echoed eerily by scientific fact. Earlier this month, a 22-person expedition donned breathing masks for protection from acid fumes and ventured a mile deep inside the cavern, Cueva de Villa Luz, or Cave of the Lighted House, about 80 miles south of the Gulf of Mexico on the edge of the Chiapas highlands. It returned with an extraordinary confirmation that the walls of the limestone cavern are genuinely alive--lined, in many places, with a layer of microbial mucus as much as half an inch thick.

The researchers, nearly all from the United States, found the dark, damp world occupied by a profusion of larger creatures, too--close relatives of surface organisms. But anchoring it all are immense colonies of yet-to-be-identified microbes. The single-celled creatures appear to be expressions of a skein of life that continues, in the pores of near solid rock, down many miles. And its bizarre microbes, like other samples of life recently found in places traditionally thought to be too hostile for any organism, may give clues to how to find life on other planets.

Microbes have been found in other caves but not in such profusion. Most geology textbooks say nonbiological processes form limestone caves. Weak carbonic acid--created as rainwater reacts with carbon dioxide in the air and minerals--the story goes, has slowly etched vast, natural hollows. More recently, earth scientists have begun to suspect that living sculptors--microbes--made those immense chambers, acid drop by acid drop.

Proof for that new theory has been hard to come by, though. In most caves, the bacteria that did the job would have died long ago. Some vaguely microbial forms have been found in North America's deepest cave, Lechuguilla, in New Mexico's Carlsbad Caverns National Park: Its nearly 1,600-foot labyrinths contain strange, fossilized structures that resemble looped string cheese and may be microbial in origin. In Villa Luz, on the other hand, "we see the same things, but they are still alive," says Louise Hose, the expedition leader and a professor of geology at little (650-student) Westminster College in Fulton, Mo. Hose has been an avid speleologist, or caver, for 20 years. Reports that not only is Villa Luz teeming with life but its microorganisms drip sulfuric acid drew her like a magnet. In the cave, she says, she was seeing Lechuguilla as it may have been millions of years ago.

"Snot-tites"? The cave's microorganisms form viscous colonies that hang like slender, pale, glistening stalactites from ceilings and overhangs. The proper term for such things is microbial veil; the researchers dubbed them snot-tites. The walls crawl with spiders and other invertebrates adapted to the foul fumes. Near the entry and in fresh-air pockets, four kinds of bats, including vampires, hang overhead and flutter about, dropping guano that squirms with maggots. A lot of the travel inside the cave is through waist-deep water, on the bottom of which is black sulfurous mud a foot deep, overlain by inches of living slime. The small fish swim everywhere, in an abundance not seen in other caves. One of the explorers, Penelope Boston, a microbiologist at Complex Systems Research Inc., a Boulder, Colo., company that does government contract research, says she emerged from Villa Luz feeling almost as though she had not entered Earth but left it. "I have always been in love with space exploration," Boston says, "and this is the closest I am going to get."

While organic material falls in from above, the cave's primary food chain starts with the immense colonies of unusual microbes. They represent scores of species, most of them new to science. Cut off from sunlight, they cannot photosynthesize. The energy that fuels the bacteria derives from hydrogen sulfide and other inorganic chemicals rising from deeper below. The drizzle of pure sulfuric acid is just one product of the microbes' stygian metabolism. "The cave is a spectacular example of an ecosystem driven not by light but by inorganic chemistry," says Norman Pace, a University of California microbiologist who plans to study many of the organisms the researchers found. "It is an interface of two worlds, the one on the surface that uses oxygen and eats organics, and the stuff down below."

The cave discovery also comes as evidence mounts that Earth's crust is shot through with microbes to great depths. In 1992, Cornell University astronomer Thomas Gold wrote a paper titled "The Deep, Hot Biosphere," which served as a spur for much of today's deep biology search. In it, he estimated that if all life inside the Earth were hauled to the surface from as much as 3 miles down, it might form a layer 5 feet thick. It would weigh more than all the life now on the surface. And that subsurface and barely explored world, scientists like Pace believe, is the main stage for the planet's biodiversity. Genes of some of these extremophiles, as scientists call microorganisms living in extreme environments, suggest they represent dozens of kingdoms of life. Outwardly similar through a microscope, at the molecular level they are as different from one another as animals are from plants or fungi. They may contain enzymes or other biological products with medical or other uses beyond the ability of chemists to invent on their own.

Government backing for such research includes a new "LExEn" program, for Life in Extreme Environments, which the National Science Foundation set up to pave the way for a search for life on other planets. So far, it has granted money for researchers to examine organisms found in Antarctic ice, in boiling hot springs, in vents on the seabed, in rock drilled from volcanic formations more than 10,000 feet deep, and in the utter dark of caves such as Villa Luz. Scientists don't know what life on other planets is like, but they can practice looking for it by first seeing how cleverly life hides on Earth.

It will take months to years, and more expeditions, to begin understanding how the cave's many organisms interact and their exact relationships to life elsewhere. Hose expects to return in April, at the time of the next fertility ceremony. And, she adds, the cave yielded benefits to more than speleology and the science of microbial veils. After the last trip, "we all noticed that our complexions were clearer," Hose says. The air inside apparently acts like a beauty parlor acid peel.