Three years ago, Hazel Barton, a biologist from Northern Kentucky University, traveled to southern Venezuela to star in an Animal Planet documentary entitled "The Real Lost World." While there, she visited Mount Roraima, the largest of the flat-topped South American tepuis. Tucked into the summit is a 10.4-km long, crystal cavern of pink and amber quartzite.
"Roraima Sur Cave is the longest quartzite cave in the world," says Barton. Most caves form in limestone, which dissolves easily in the slightly acidic ground water that leaches from microbe-rich soils. But that process doesn't explain how Roraima Sur was carved out of quartzite, which is highly resistant to chemical deterioration. The walls of the cave crumbled in her hands, and chambers were loaded with opal "soda straws," a geological novelty found nowhere else in the world. "I went in there and was like, 'Holy crap, look at all these microbes!'" says Barton. Could they be responsible for the cave's formation?
One icy February morning inside the biology building at Northern Kentucky, Barton makes time to meet me between a National Science Foundation-sponsored training course in Antarctica and a trip to Hungary. In her office, a stuffed bat hangs from the ceiling. A bumper sticker on the door reads: "Sure, I crawled out from a rock. I'm a caver."
I trail behind the 36-year-old redhead as she races down three flights of stairs for a coffee and then rushes back up. The conversation swiftly moves from the mountains of New Zealand to a 200-km long cave in the backcountry of New Mexico. Barton started caving when she was 14 years old. Since then, she estimates that she's visited between 500 and 1,000 different caves, often more than 50 in a single year.
For a while at least, she tried to keep her biological interests and her caving interests apart. But that all changed when she did a postdoc with Norman Pace at the University of Colorado, Boulder. "He pointed out that I could do microbiology in places other people couldn't go."
Barton and Pace decided to do a quick study of microbes on the wall of Fairy Cave in Glenwood Springs, Colorado. "We thought it would be simple, but it turned out to have a phenomenal amount of diversity." Their molecular phylogenetic analysis indicated that there were 38 unique organisms affiliated with the Proteobacteria, Actinobacteria, and Cytophagales. But none of her sequences corresponded closely with known sequences in other caves or on the surface. Barton mined the sequence data to speculate on how so many species were surviving in such a low-energy environment. The bacteria seemed to be either digesting rocks and fixing airborne gases, or scouring for the tiniest traces of organic nutrients ( Geomicrobiol J, 21:11-20, 2004).
Since 2004, Barton has focused on understanding speleogenesis (the creation of caves), and in particular how microbes are responsible for the complex architecture that has been previously attributed to geological processes. It took two years for Barton to get the permits and funding to return to Roraima Sur on a full-scale expedition.
Barton reaches into a cabinet and pulls out a crumbling piece of quartzite from that trip. Quartzite can dissolve in acids only if the pH drops below 2.0, which is into the range of lemon juice or stomach acid. On the other hand, the pH has to rise just above 8.5, into the range of seawater and baking soda, before it is alkaline enough to dissolve the rock. Indeed, her group has found that ammonia has been accumulating in the quartzite, and measurements indicate that moisture in the cave is alkaline. The remaining question is whether or not microbes are indeed spewing out the ammonia and chewing into the quartz - a biological first.
In an airtight chamber, Barton is trying to culture bacteria from the cave, but she's not raising them on agar plates. "We're trying to force them to take nitrogen from the atmosphere, to see if they can do it and how well they do it," she says. Other culture plates offer the Roraima microbes just nitrate, which they should be able to convert to ammonia. "The idea is that you have these organisms that pull nitrogen in, and that drives the whole system in the cave."