Scientists have identified a new species of microscopic worms living in the ground below South African mines, isolated from fracture water gushing up from miles below the Earth's surface. It is the first multicellular organism to be found at such depths.
The discovery of the tiny nematode (named Halicephalobus mesphisto after Mephistopheles, a literary nickname for the Devil), published in this week's issue of Nature, challenges the assumption that deep subsurface ecosystems cannot support multicellular life and may have implications in the search for life on other planets.
"Up until this time, all these [deep subsurface] systems were thought to be prokaryotic," said Jim Fredrickson, a biologist at the Pacific Northwest National Laboratory who was not involved in the research. The paper makes "a very compelling argument" that such environments could also house more complex organisms, he added.
Scientists have often assumed that deep subsurface environments, miles below the surface, cannot support multicellular life because of the pressure, hot temperatures, and lack of oxygen and space. But after identifying nematodes in deep caverns in Mexico, Gaetan Borgonie, a nematode expert at Ghent University in Belgium, reached out to Tullis Onstott at Princeton University about searching for nematodes at Onstott's field site in the deep mines of South Africa. Nematodes, Borgonie hypothesized, might be able to live in extreme deep environments because of their ability to enter a "survival" mode and live for extended periods of time without oxygen.
The more he learned about nematodes, the more Onstott began to believe that nematodes could live at extreme depths. "That changed my perspective," said Onstott. "If there's just enough oxygen down there, these nematodes could function."
The researchers sampled fracture water, which flows up from deep cracks in the Earth's crust, that was expelled from high pressure valves at six sites within the mines. In the water, which turned out to be some 5,000 years old, they found half-a-millimeter-long nematodes. The nematodes turned out to be a new species, which the team named after Mephistopheles, a reference to Devil from the Faust legend in medieval literature.
The team then spent two years doing various control experiments to verify that the worms were not a result of surface contamination from the formation of the mines or the mining process. They tested the water used to dig the mine and soil samples from around the mine, and isolated no nematodes.
The data suggest that nematodes could be found in other deep subsurface settings, said Onstott. In addition, scientists may expand our search for life on Mars and other planets to include multicellular organisms in subsurface habitats, he adds.
Still, notes Fredrickson, the researchers only found the nematodes in a handful of samples, so it would be important to confirm that multicellular life is an important part of a deep subsurface ecosystem at additional sites. "It remains to be seen whether or not this is really a common organism in such environments," said Fredrickson.
G. Borgonie, et al., "Nematoda from the terrestrial deep subsurface of South Africa," Nature, 474:79-82, 2011.