Science News - July 2, 2011

3. 6 kilometers

Maximum depth of nematode DNA detected

1. 3 kilometers

Deepest worm found in South African mine

450 meters

Previous depth record for complex life

Alive and well, deeper underground
than any other life has gone before
Worms in South African mines extend limits of habitability

“If it can work its way through the
fractures and keep on picking up good-
ies, it doesn’t really care about how deep
it is,” says Onstott. “Given enough time,
these organisms will get there.”
Nematodes can live with hardly any
oxygen; the limiting factor to their sur-
vival in the deep is probably the high
temperatures found there, Borgonie
says. In lab cultures H. mephisto survived
temperatures up to 41° Celsius.

But R. John Parkes, a deep-biosphere expert at Cardiff University in Wales, questions whether drilling boreholes for the mines altered the subsurface environment somehow, perhaps by introducing more oxygen or otherwise providing an artificial environment in which nematodes could thrive.

In a few months Borgonie will return to South Africa to hunt for new nematodes in mine water that he has been collecting and filtering for two years— far longer than the 24-hour samples he reports on in the new study.

Karsten Pedersen, a microbiologist at the University of Gothenburg in Sweden, says he is convinced by the hard work the team did to rule out the possibility of surface contamination. Pedersen has found yeast up to 450 meters deep in Swedish granite, the previous record holder for complex subterranean life, but hasn’t yet looked for nematodes there. More research is needed, he says, to confirm whether the South African deep worms are a rarity or the rule. s

By Alexandra Witze

Tiny worms appear to live in rock fractures up to 3. 6 kilometers underground, researchers have reported, far deeper than anyone has encountered complex organisms before. The discovery of nematode worms in three South African gold mines underscores the fact that Earth’s biosphere reaches well into subterranean realms. It also suggests that habitable environments may exist buried way down on other planets, such as Mars.

Worm specialist Gaetan Borgonie and his colleagues present their findings, which include a new nematode species named after Faust’s devil Mephistopheles, in the June 2 Nature. Nematodes are an incredibly diverse group encompassing numerous intestinal parasites and the widely studied laboratory roundworm C. elegans.

Over the last few decades, researchers have found plenty of bacteria and other single-celled creatures thriving deep underground. But “to actually go out and start looking for multicellular organisms is such a game changer. Nobody in their right mind would think they were down there,” says team member Tullis Onstott, a geomicrobiologist at Princeton University.

But Borgonie, of the University of Ghent in Belgium, thought there just might be enough food, water, oxygen and other nematode necessities to keep worms alive deep in Hades’ realm. So he traveled to South Africa to collect water and soil samples from six boreholes.

In the deepest, 3. 6 kilometers down at the Tau Tona gold mine, Borgonie found traces of nematode DNA in water oozing from rock fractures. Much shallower, 900 meters down the Driefontein gold mine, he found actual nematodes of

The discovery of the worm Halicephalobus mephisto 1. 3 kilometers deep in a South African mine suggests that complex life can thrive deeper in the Earth than scientists had suspected.

two known surface species. And at the middle depths, 1. 3 kilometers down in the Beatrix gold mine, he uncovered an odd-looking, living female nematode.

Back in the laboratory, Borgonie laid
that worm under a microscope. “It was
like an intensive care unit — I was looking
at it every hour,” he says. “The only thing
I wanted it to do was lay an egg.”
It did. Eight of them. Borgonie had
the start of a worm dynasty. About half
a millimeter long, the nematodes are
different enough from other species to
warrant their own name: Halicephalobus
mephisto.

To make sure the worms weren’t accidentally brought down by mine workers, the researchers ran a series of painstaking tests. The studies showed that the water in which the nematodes live is at least several thousand years old.

Before that, Borgonie says, ancestors of the newly found worms probably lived on the surface. Over generations they presumably slithered down, munching bacteria along the way.

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