In an Unlikely Place, Life Has Been Percolating

First there was the microbe that scientists called "The Bold Traveler," found living in lightless solitude more than two miles down a South African gold mine. Nothing alive had ever been found in rock fractures at that depth before.

Then there was the "Worm From Hell," the first complex, multicellular creature (a type of worm) found living at almost equal depths in the same group of mines.

Now the researchers who made both of those discoveries have hit another jackpot: the discovery of a "veritable zoo" of multicellular creatures living in the wet rock fissures of the gold and diamond mines of the Witwaterstrand Basin of South Africa, roughly a mile below the surface.

The earlier discoveries (reports about them were published in 2008 and 2011) had already dramatically changed scientists' understanding of life in the underworld. They had also given encouragement to those convinced that microbes and maybe multi-celled creatures can survive deep below the surface of Mars and other moons and planets. The latest jackpot carries this shift in thinking further, potentially into some new realms.

"It is very crowded in some places down under," said Gaetan Borgonie of ELi, a Belgian nonprofit that studies extreme life, and of South Africa's University of the Free State in Bloemfontein.

Borgonie, lead author of a paper about the "veritable zoo," said that his discovery in 2011 of a new species of nematode at great depth had been dismissed by some as a "freak find." But now, he said, "the fact that we have found in two mines, in different water, two ecosystems with several types of invertebrates hopefully puts that notion to rest as wrong.
he called the findings, published this week in the online journal Nature Communications, "particularly good news for Martian research, because if life ever arose there, these findings suggest it may be more likely to remain alive in the subsurface," where it would be protected from radiation on the Martian surface.

Borgonie has been working with Princeton University's Tullis Onstott, who pioneered the search for extreme life in the South African mines, the deepest man-made cuts in the world.

Onstott said the number and variety of creatures - worms in particular - found so deep underground was "just startling." He said the paper makes clear that previous estimates of the amount of life (biomass) underground and under the bottom of the oceans have been too low. Those estimates have ranged from 20 to 50 percent of the total mass of life on Earth.

The subterranean zoo was collected over a two-year period from water that was determined, by carbon dating, to have rained down more than 12,000 years ago. It then made its way deep underground through rock cracks and mine fissures.

The water now flows out of boreholes that miners drilled deep into their tunnel walls long ago to check the geology and to identify potentially problematic gas and water pockets. The tiny creatures being collected now from borehole water could be the distant progeny of ancestors that arrived long ago with the water, the researchers said.

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To set up their equipment, Borgonie and his teammates had to go through quite a journey. They descended about a mile in the mine elevator and began their trek, crawling over a wall, squeezing through tight openings, wading through knee-high water, climbing more than 100 steps up a rusted and rickety ladder to a pump station perch - all while carrying heavy backpacks in punishingly hot temperatures. (The deeper you go down, the hotter it gets.)

And they did this occasionally for months on end. One of the boreholes they tapped was filtered continuously for the full two years, which allowed for the collection of so many creatures.

The zoo they collected featured many kinds of worms, fungi, protozoa and crustaceans - creatures with more complexity than bacteria and other microbes.

Often the creatures were living in biofilms, filmy collections of bacteria and other life held together in the water by secretions that encase them and hold them together. Borgonie recorded some of the borehole biofilms with an endoscope, the first video documentation of life in rocks at this depth.

"It has become increasingly apparent that deep rock fractures are excellent places for life to exist," said Frederick Colwell, a professor of microbiology and astrobiology at Oregon State University, who was not involved in this study.

"There are limits to how deep life can survive - based on temperatures, pressure, access to nutrients and oxygen," he said. "But those limits are being redefined these days."

Colwell, like the Onstott-Borgonie teams, sees no reason why deep subsurface life would exist in South Africa but not many other parts of the world, including under ocean floors.

Research into deep subsurface life has spawned some provocative theories, especially the one promoted by Swedish microbiologist Karsten Pedersen. He says the most recent findings add to his hypothesis that life on Earth began deep below ground - where conditions are extreme but stable - rather than in water on the surface, as scientists generally propose.

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"These new observations support this origin of life by expanding the range of organisms than can survive deep below the ground surface of our planet," he said. "So we know that microbial life is well adapted to live in deep aquifers of fractured rock, which are the possible birthplace of all life on our planet."

A primary hurdle the South Africa mine teams have to overcome is proving that the microbes and creatures they find have not come from the shoes or clothing of miners or through mine ventilation water. The contamination issue was resolved through extensive testing of the soil and mining water, which contains two disinfectant bleaches that would kill the life-forms that have been discovered. What's more, the water that is being filtered and tested for living things comes directly from inside the rock face.

Borgonie writes that the creatures he collected all have twins and cousins on the surface, and so are not new species or necessarily extremophiles, which are creatures that live in scalding, freezing, super-salty, high radiation and other extreme environments. They have instead adapted to life deep underground, he said. This is different from the far more ancient "Bold Traveler" bacterium, D. audaxviator, which evolved during its millions of years deep underground and has no aboveground direct relative. The "Worm From Hell" was also determined to be a new species, H. mephisto.

Another discovery by Borgonie, published in the journal Frontiers of Microbiology in August, featured nematodes inside stalactites attached to deep tunnel ceilings. The find was striking because of their chosen homes but even more because at least one of the species, M. Parvella, is known to survive only in saltwater on the surface, yet somehow lived inside stalactites with salty water deep down.

Since no saltwater ocean had existed on the surface in this region of South Africa for millions of years, Borgonie said the most puzzling question is how saltwater was present for the creatures as they descended and survived. And that raised an even more complex question: When might these saltwater-dependent creatures have arrived at their subterranean home? Perhaps it was millions of years ago, Borgonie said, making their survival at such depths all the more remarkable.

"This study shows that Earth's microscopic and near-microscopic life is amazingly versatile, with organisms including tiny animals able to thrive deep below Earth's surface," said Carl Pilcher, director of NASA's Astrobiology Institute. "The subtitle for this paper could be 'Biofilms can grow anywhere.' And that should probably be what we are thinking as we explore other planets and delve into their subsurfaces in search of habitable environments