globe-spanning underground bacterial networks

NatGeo | Though the calling card of the horseshoe-shaped Cave of Crystals may be its massive mineral formations, some of its biggest surprises are literally microscopic.

In 2008 a team of scientists, including New Mexico Tech's Boston, investigated the cave and found microbial life living in tiny air pockets in the crystals.

In December 2009 Boston returned to the cave with another team. From pools of water that hadn't been present during her first trip, the scientists collected bacteria as well as viruses that prey on the bacteria—something that was suspected but had not been confirmed on the first expedition.

Viruses, after all, are among the "primary predators of bacteria," explained Danielle Winget, a biologist at the University of British Columbia, in the new documentary.

Sure enough, the team found as many as 200 million viruses in a single drop of Cave of Crystals water.

But the virus finding was perhaps not the expedition's most surprising microbial discovery. Analysis of bacterial DNA from the Cave of Crystals showed that the tiny life-forms are related to microbes living in other extreme environments around the world, including caves in South Africa and Australia as well as hydrothermal vents (video).

"We're picking up these patterns of similarities in places that are geographically widely separated," Boston said.

That similarity and separation adds up to a mystery, according to Curtis Suttle, a biologist at University of British Columbia and a member of the 2009 Cave of Crystals expedition.

"We don't really understand how it is that the organisms in a hydrothermal vent in Greece or a deep gold mine in South Africa are related to organisms that we find in a subsurface cave" at Naica, Suttle said.

"It's hard to imagine some kind of underground [network] connecting South Africa with Mexico."

Alien Underworlds

As mind-boggling as the idea of a possibly globe-spanning, underground bacterial network may be, some scientists see potential links between the Cave of Crystals and even farther-flung hot spots—for example, extreme environments on Mars and other worlds.

Though Martian geology might be more static overall than Earth's, "there may be residual pockets of geothermal activity that could provide a zone where water could be liquid and where chemically reduced gases from below can percolate up and act as a nutrient source," as in the Cave of Crystals, Boston said.

(See "Mars Has Cave Networks, New Photos Suggest.")

Poirier, the Ontario astrophysicist, agreed.

"For Mars, our best bet of finding life is to look underground," Poirier said. "So there are a lot of parallels between humans exploring subterranean caves looking for microbes and Martian exploration in the future."

If the caves on Mars are anything like the caverns beneath Naica mountain, she said, future Martian explorers will have to be trained to ignore the strange sights surrounding them.

"When you're in the caves, you're overwhelmed by the [harsh] conditions, but you're also overwhelmed by the beauty, and it's really hard to maintain your focus," she said.

Even if scalding water submerges that beauty tomorrow, Boston said, the caves' scientific potential should live on, thanks to the multitude of samples already collected.

"My usual rule of thumb is for every hour you spend in the field, you spend at least a thousand hours on analysis," Boston said. "So we've got our hands full."