Tucked beneath the desert in southern Arizona is Kartchner Caverns, a maze of remote, largely uninhabited underground passages and caverns that are cloaked in perpetual darkness. But this seemingly desolate cave system actually plays host to a surprisingly diverse array of microbes that survive underground despite the extreme dearth of light and nutrients, according to a new study.
A team of researchers led by scientists at the University of Arizona in Tucson discovered communities of microorganisms that live in the limestone caves of Kartchner Caverns State Park. These microbial ecosystems thrive by teasing out the limited nutrients in water runoff that drips into the cave through cracks in the cave's rocky exterior, the researchers said.
The unexpected discovery, published online Sept. 12 in the journal of the International Society for Microbial Ecology, could help scientists understand how bacteria, fungi and other microbes survive in extreme environments. (Extreme Life on Earth: 8 Bizarre Creatures)
"We didn't expect to find such a thriving ecosystem feasting on the scraps dripping in from the world above," Julie Neilson, an associate research scientist in the University of Arizona's College of Agriculture and Life Sciences, said in a statement. "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."
Living in darkness, the underground microbes are unable to carry out photosynthesis— the process that plants and other organisms use to convert sunlight into energy. Still, the types of microorganisms found in Kartchner Caverns shared similarities to the more familiar types found on the Earth's surface, the researchers said.
"We discovered all the major players that make up a typical ecosystem," Neilson explained. "From producers to consumers, they're all there, just not visible to the naked eye."
Even without such biodiversity, simply living off the water dripping into Kartchner Caverns is an impressive feat, as there is a shortage of organic carbon — one of the building blocks of life on Earth — within the cave.
"Kartchner is unique because it is a cave in a desert ecosystem," Neilson said. "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."
These cave-dwelling microorganisms cultivate what little nutrients and energy are locked in the water molecules from decaying organic matter in the soil above ground, or from minerals dissolved in the rock fissures, the researchers said. The microbes have adapted means of using the chemical compounds present in the cave — in some cases, even eating rock to get energy from compounds such as manganese or pyrite, Neilson said. (7 Theories on the Origin of Life)