A Living Desert Underground

UA scientists have discovered diverse communities of bacteria, fungi and archaea on the surface of Kartchner stalactites that live off of nutrients from the cave drip water and contribute to the growth of the cave formations through calcite precipitation. (Photo: Bob Casavant/Arizona State Park Service)
UA scientists have discovered diverse communities of bacteria, fungi and archaea on the surface of Kartchner stalactites that live off of nutrients from the cave drip water and contribute to the growth of the cave formations through calcite precipitation. (Photo: Bob Casavant/Arizona State Park Service)

Hidden underneath the hilly grasslands studded with ocotillos and mesquite trees in southeastern Arizona lies a world shrouded in perpetual darkness: Kartchner Caverns, a limestone cave system renowned for its untouched cave formations, sculpted over millennia by groundwater dissolving the bedrock and carving out underground rooms, and passages that attract tourists from all over the world.
 
Beyond the reaches of sunlight and seemingly devoid of life, the caves are in fact teeming with an unexpected diversity of microorganisms that rival microbial communities on the earth's surface, according to a new study led by University of Arizona researchers that has been published in the journal of the International Society for Microbial Ecology. The discovery not only expands our understanding of how microbes manage to colonize every niche on the planet but also could lead to applications ranging from environmental cleanup solutions to drug development.
 
"We discovered all the major players that make up a typical ecosystem," said Julie Neilson, an associate research scientist in the UA's College of Agriculture and Life Sciences. "From producers to consumers, they're all there, just not visible to the naked eye."
 
In a long-standing collaboration between Kartchner Caverns State Park and the UA, Neilson and her co-workers have spent years exploring the underground world and its inhabitants. For their latest study, they swabbed stalactites and other cave formations for DNA analysis. Based on the genes they found in their samples, they reconstructed the bacteria and archaea - single-celled microorganisms that lack a cell nucleus - living in the cave. Kept secret for 14 years after its discovery in 1974 by two UA graduate students who were hiking in the Whetstone Mountains just south of Benson, Ariz., Kartchner Caverns has been protected from human impact so that scientists can study the fragile environment and organisms inside the cave.
 
"We didn't expect to find such a thriving ecosystem feasting on the scraps dripping in from the world above," Neilson said. "What is most interesting is that what we found mirrors the desert above: an extreme environment starved for nutrients, yet flourishing with organisms that have adapted in very unique ways to this type of habitat."
 
Unlike their counterparts on the surface, cave microbes can't harness the energy in sunlight to build organic matter from carbon dioxide in the atmosphere. This process, known as photosynthesis, forms the basis of all life on Earth.
 
In the absence of light, bacteria live off water runoff dripping into the cave through cracks in the overlying rock and harvest the energy locked in compounds leaching out from decaying organic matter in the soils above and minerals dissolved within the rock fissures, Neilson and her team discovered.
 
"Kartchner is unique because it is a cave in a desert ecosystem," Neilson explained. "It's not like the caves in temperate areas such as in Kentucky or West Virginia, where the surface has forests, rivers and soil with thick organic layers, providing abundant organic carbon. Kartchner has about a thousand times less carbon coming in with the drip water."

Read the rest of this November 19 UANews article at the link below.

For more information about a new educational kiosk designed by CALS faculty for the Kartchner Caverns Discovery Center, please read Cave Microbes Exhibit Now Open at Kartchner Caverns.

Date released: 
Nov 22 2013
Contact: 
Julie Neilson