Antarctic Microbes Colonize under Mars-like Conditions
Dry Valley, Antarctica map.
The dry, salty valleys of western Antarctica are hostile. Mean annual temperatures rarely reach above minus 30-35 degrees Celsius (~ minus 90 Fahrenheit). Less annual rainfall than 10 mm (0.4 in) makes these glacial conditions nearer to desertified and rocky soil. Much like similar weather on Mars, dessication or deep-freezing of virtually any exposed microbes seems inevitable.
But returning from a microbe-gathering trip to what in Western Antarctica is called the Quartermain Mountains, a research consortium from 3 countries (Canada, US, and New Zealand) sampled a fascinating colony of fungi. Their new results raise the question: without tapping an obvious liquid water supply, how do such fungi make a living there? Perhaps relying on the high-salt soils to access water below its normal freezing point, these fungi give astrobiologists some new candidates for survival studies in such harsh settings.
The research team included colleagues from the Royal Military College, Toronto and York universities in Canada, science teams from Arizona and New Mexico, along with New Zealanders from the private sector (Geochemical Solutions) and the government Land and Soil Consultancy Service. They published their analysis of the Antarctic old soils (paleosols) and fungi discovery in the journal Icarus. As a potential guidepost to study dry, cold soils on Mars, the team entitled their new study, "Morphogenesis of Antarctic Paleosols: Martian Analogue."
More than 20 years ago, scientists first discovered that algae, fungi and bacteria could grow inside porous sandstone and surface pavement in the Antarctic Dry Valleys. Since the 1980’s researchers have found other active niches for diverse Antarctic biology: long-lived algal mats submerged under 10-foot-thick lake ice crust and bacteria living in hot volcanic fumaroles of Mount Erebus. But by digging 1 to 3 inches below the soil top-layer, the American and New Zealand teams seemed to have uncovered what may prove to offer some surprising survival pathways for the sub-surface fungi.
"We went to the iron-rich horizons, where we thought we’d find lots of microbes, because microbes need iron for physiological processes," William Mahaney of York University said. "And we sampled the lower-down, high-salt horizons, where we thought we would find few microorganisms. We found just the opposite."
Their new collection included long-lived colonies of insecticidal (insect-killing) fungi and a common species of Penicillium bacteria. "The strange thing is, we found several colonies of Beauveria bassiana — fungi that thrive on insects," said Mahaney. "The colonies may have been there longer than centuries, maybe millennia, maybe since the last Ice Age — I have no idea how long. So the question is, what do these well-developed colonies live on?"
Finding out how the microbes live in the harsh Dry Valley region is one job for David Malloch of the University of Toronto (who analyzed the microbes), and some guesses have already been put forward. "Many fungi are able to tolerate low temperatures, dryness, dormancy, low nutrient levels, etc.", says Malloch. "You would fully expect to find fungi and other microorganisms in the Antarctic provided some liquid water is occasionally available and some organic carbon is present for their nutrition."
But liquid water is very rare in the Dry Valley. One plausible way to adapt to the Antarctic deep-freeze is to colonize high-salt soil, because salt lowers the apparent freezing point of liquid water. "We found microbes in soil with 3,000 ppm salt concentrations," Mahaney said. "That’s so much salt, temperatures can drop to minus 56 degrees Celsius before there’s frost bite." In Antarctica particularly, such salty soil may build up from wind-blown ocean salt and the churning of soil by slow, but persistent glacial migrations.
The Ancient ‘Living’ Supercontinent
|Sandstone algae found in Antarctic rocks.
Credit: British Antarctic Society-BAS
One important question to answer is "when did these ancient microbes get their start in Antarctica, particularly if categorized as primarily insect-fungi?" To answer that, one has to revisit the shifting map of Earth, and an ancient time when Antarctica might have harbored some form of insect life. (In fact Antarctica, Australia, New Zealand, Africa, South America and India were once part of a supercontinent called Gondwana. About 100 million years ago, it broke apart, and the land masses slowly drifted into their current positions. But before that happened, Antarctica enjoyed a warm tropical climate that supported an array of remarkable animals. In fact, about 560 million years ago, Antarctica was north of the equator. Today, no known large land mammals are found anywhere in Antarctica.)
The soil uncovered by the research team dates the fungal colonies to around 10-15 million years old, when Antarctica was likely less hostile than its present day South Pole extreme. To test the age of the fungi, the scientists used a tracer of biological activity, much like carbon dating, but instead relying on another chemical isotope, beryllium-10.
"The main issue here is the age of the parent material and the soil formation," says Vic Baker of Arizona. "Carbon 14 can only be used back to about 40,000 years, whereas [beryllium] Be-10 can be used back 10 million years. Also the sample requirements of organic carbon for the C-14 method cannot be met in Antarctica."
Survival of the fittest in an unfit place
Many scientists are no longer surprised at the robust tolerances found in microbe adaptation, whether those microbes scavenge a living from dry, salty, hot or very cold landscapes. This revised view of what constitutes a tolerable biological condition on Earth, in fact, makes it somewhat surprising when sterile samples are found anywhere on Earth. Such microbes may indeed have a relative (if not absolute) survival advantage over competing lifeforms: "In soils with such a paucity of life," says Malloch, "there may be more food than eaters. [A fungal] presence there may have more to do with tolerance to the physical environment than to lack of nutrients."
If dormancy, sporulation or high-salt soil makes the fungi viable, their presence in sub-surface deep-freeze has the research team intrigued: "They (fungal colonies) were there," says Malloch. "I am convinced of that. I have no idea whatsoever what state they were in at the time the soil was collected."
For the intrepid tourist, a trip to the hyper-arid, ultra-cold climate of the Antarctic Dry Valleys comes closer to present-day Martian climate than anywhere on Earth.
Further experiments to understand how the fungi cope with such hostile environments are forthcoming. Concludes Malloch: "We don’t yet know much about the origin of these materials nor in fact do we really know much about the capabilities of the fungus. However, these questions can be answered by straight-forward experimental work. The results of such studies may further support the idea that conditions on Mars could sustain life but ultimately someone will have to go to work on the real thing."
But looking skyward for what elsewhere in the solar system might match Antarctica still offers a kind of reference point for planning strategies to sample Mars. As the authors’ analysis in the journal Icarus concludes: "We believe that our field-based investigation of parts of the Antarctic yields valuable information about soils and microbial life that may bear significantly on future manned and unmanned missions to Mars, especially since the martian surface archives an active and varied geologic history similar in many ways to that of Antarctic terrains."
Collaborators on the investigation include: William C. Mahaney of York University in Ontario, Canada; James M. Dohm and Victor R. Baker of the University of Arizona; Horton E. Newsom of the University of New Mexico; David Malloch of the University of Toronto (who analyzed the microbes); R.G.V. Hancock of the Royal Military College, Ontario, Canada; Iain Campbell of Land and Soil Consultancy Services, Stoke, New Zealand; Doug Sheppard of Geochemical Solutions, Petone, New Zealand; and Mike W. Milner of York University.