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."
"The cave microbes make a living off the extremely limited nutrients that are available," Neilson said. "Instead of relying on organic carbon, which is a very scarce resource in the cave, they use the energy in nitrogen-containing compounds like ammonia and nitrite to convert carbon dioxide from the air into biomass."
The researchers found evidence of cave microbes engaging in all six known pathways that organisms use to fix carbon from the atmosphere to make food and structural material.
Neilson said although the nitrogen-driven pathway is probably the most dominant in the cave, there might be others. Some microbes even eat rock to derive energy from chemical compounds such as manganese or pyrite.
|Contact: Daniel Stolte|
University of Arizona