Caves provide one of the most constant of environments; the temperature and humidity remain the same. But in some caves, hydrogen sulfide combines with oxygen to produce sulfuric acid. Some bacteria add their own acid as a waste product. To protect themselves, bacteria produce their own microenvironment within the slimy biofilm.

"It acts as a place for them to conduct their own little chemistry labs, so to speak, regardless of what is going on outside of the film," says Boston, a microbiologist at New Mexico Tech, in Socorro. "We protect ourselves (sometimes ineffectually) against the byproducts of our metabolism, everything from simple waste products like feces to the toxic substances resulting from our industrial efforts," Boston says. "In essence, the bacteria are doing the same thing."

Building snottites

While that acid-producing bacteria appear to etch away the limestone of caveshelping to produce the soft, crumbly stone cavers call punk rocksome cave bacteria create crystals, actually producing new rock, much like dripping water deposits limestone stalactites. If the colony is growing on the underside of a ledge or on a roof, they build a slimy projection the team calls a snottite.

The mineral portion of a snottite carries a bacterial signature in its crystal formation, so a snottite sample from Mars, say, could be distinguished from a small stalactite.

Walls dripping with slime may seem like a scene from a horror movie to some, but not to Northup. Vast colonies of bacteria coat the walls of some Hawaiian lava tubes, Northup says. "Theyre really cool because when you shine your light on them at certain times of the year it looks like somebody has silvered the walls. Its just breathtakingly gorgeous. Its so thick, I saw where people had written their names in the slime."

Finding new species

Other caves, such as Lechuguilla in New Mexicothe deepest cave in the continental United States and a favorite of the slime teammay appear nearly devoid of life, Northup says.

"In a cave like Lechuguilla, if you didnt know from microscopy that there were microbes there, you would never guess it. The only place you see them is a place called Pink-Dot Pool, where there are actually colonies of bacteria floating. Whether thats a matter of contamination or not, we dont know," Northup says.

Nonetheless, both bacteria and archaea call Lechuguilla home, many using gasses as sources of energy: hydrogen sulfide, carbon monoxide and formaldehyde, for example.

Northup extracts and sequences DNA from bacteria in the several caves the team studies. In some cases, the bacteria represent new species. But even in the age of desktop DNA analysis, if the researchers want to learn how the bacteria eke out a living, they still need to grow them in the lab not always an easy chore.

"DNA analysis provides no information on the metabolism, physiology, ecology, biochemistry, or geomicrobiology of a strain, Boston says. "It cannot reveal the amazing chemical and mineralogical talents of organisms. Only growing them in the laboratory and hoping to induce them to perform feats of bacterial derring-do reveal those processes."

So Boston cooks up new recipes for growing the bacteria in the lab, all the while maintaining the constant temperature and humidity of the original cave. The process should begin, the team found, even before they bring the bacteria out of the cave. Larry Mallory, of Biomes, Inc., a pharmaceutical company formed to search for novel drugs made by cave microbes, discovered that starting the bacterial culture in the cave produces better yields of difficult-to-grow species.

"The results are consistently better by using their natural cave environment as their first incubator," Boston says.

In Lechuguilla, the team has kept bacteria growing in cultures in the cave for almost a year. Furthermore, they have begun growing bacteria on faux cave rock, and even glass slides, hoping to bring out even richer bacterial samples.

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