Dubbed the “worm from hell,” Halicephalobus mephisto is one of four species of nematodes recently discovered by researchers more than 2.2 miles beneath the surface of the earth in South African gold mines. Multi-cellular organisms have never been detected at such depths before.
The study, led by Ghent U. biologist Gaetan Borgonie and Princeton U. geology professor Tullis Onstott, published its findings early last month and has since received extensive international news coverage.
Prior to this discovery, scientists widely believed that only single-celled organisms, like bacteria, populated the inhospitable deep subsurface areas of the planet. However, decades of research on nematodes, a diverse family of multi-cellular roundworms, convinced Borgonie otherwise.
“I had a good idea that they could survive with any amount of environmental stress,” Borgonie explained. “Nematodes are very robust.”
In collaboration with Onstott, who had already established geological research in the world’s deepest mines in South Africa, Borgonie brought together colleagues to help search for the worms in deep fracture water samples extracted from the mines.
“We knew that there are worms in deep sea vents due to unusual symbiotic relationships. What if these creatures were also in deep fracture water?,” Onstott said.
The research produced four species of nematodes, each collected from a separate borehole. Not only do these worms live solely on bacteria and reproduce asexually, but they also endure very low oxygen levels, high temperatures and immense pressure.
The discovery of these subsurface multi-cellular organisms holds interesting implications for scientists’ understanding of evolution and the search for extraterrestrial life.
One of the species, H. mephisto, had never been seen before. Although the species is not morphologically exceptional, Borgonie noted that “it is one of the smallest nematodes. Generally free-living nematodes are approximately 30 percent bigger.”
According to Onstott, the species also has certain genetic differences that he hopes to further explore, as the presence, lack or mutation of various genes may provide insight into H. mephisto’s ability to withstand extreme environmental conditions.
Although they do not know how, Onstott and Borgonie said they assumed that both the worms and the bacteria found their way miles beneath the earth’s surface a long time ago. It is unlikely that they always existed at such depths.
“We don’t know how long they have been underground,” Onstott added. “Trying to get a constraint on that is very hard.”
In addition, nematodes may not be the only multi-cellular organisms living that deep.
“I was a little surprised to only find nematodes. Perhaps our samples were too small and insufficiently abundant to see if there is a complete biosystem down there,” Borgonie said.
Onstott, who also teaches a course on the emerging field of astrobiology, GEO 255/AST 255/EEB 255/CHM 255: Life in the Universe, believes that the discovery gives further hope to the search for life on other planets in our solar system, such as Mars.
“If you were to drill down a kilometer into the surface of Mars, you might expect to find something similar. It is not beyond the realm of possibility, given enough space, water and bacteria,” he said.
NASA is set to launch its third Mars rover, Curiosity, in late November to continue experiments that test whether the Martian landscape is capable of supporting microbial life. Onstott said he believes that additional research on the interaction between the nematodes and their subsurface abodes may yield new information that will aid NASA’s mission to locate extraterrestrial biomarkers.
Neither Onstott nor Borgonie anticipated the media attention the study has received over the last month from around the world, they said.
“I had absolutely no idea that something so small would become so big,” Onstott noted.
“Ever since it was published, I have had an interview every week. I have never seen a reaction like this before,” Borgonie said, “This is the best I have ever done and likely to ever do.”
But he added with a chuckle, “We did choose the name ‘mephisto’ [a pseudo-Greek word alluding to the Devil], and it is kind of catchy for the press.”