Amazing Survivors
Extremophiles are organisms capable of living in conditions that would kill other life-forms, including intense cold, heat, pressure, dehydration, acidity/alkalinity and other chemical and physical extremes. A few animals, such as frogs that freeze solid in winter, can qualify. But in large part, the world's endurance champs are microbes: bacteria and archaea.
They're at home in some of the most forbidding pockets of the planet, where scientists are studying their survival mechanisms—and probing the outermost boundaries of life.
Dry Life
Life can't exist without any water. But research is showing how shockingly little is necessary. Even in the planet's driest places—such as the Atacama high desert in Chile or the Dry Valleys in Antarctica—scientists have found that microbes can set up shop a few inches below the surface. In such circumstances, certain extremophiles have evolved novel biochemistry with functions that compensate in some respects for lack of water. Investigators are studying the DNA of these survivors to determine which genes contribute to the cells' abilities.
Other organisms found in Atacama and elsewhere can enter a seemingly lifeless, freeze-dried state, reviving only if and when some water appears. In the ultra-arid Dry Valleys, for example, researchers recently discovered that a mat of cells that had been dormant for two decades began photosynthesis within a day of exposure to liquid water. And a few marvelous microbes, tested in experiments on the space shuttle, have even survived the vacuum and radiation bombardment of empty space.
Cold Life
Lots of creatures can live in the cold. But it takes special talents for cells to survive at the South Pole, where temperatures often drop below -100° F. Yet that's where scientists found a certain kind of bacteria that can get through the polar winter and have active metabolisms in surroundings as cold as 1.4° F.
That's just one of many creatures specially adapted to extremely frigid venues. Researchers uncovered microbes in an ice core extracted from just above Lake Vostok, an ancient body of water buried thousands of feet below the Antarctic ice surface. At the other end of the Earth, extreme-tolerant organisms have shown up in the permafrost of northern Alaska.
Laboratory studies have shown that many cold-surviving life-forms (collectively known as psychrophiles) have remarkable cellular ingredients that prevent the formation of ice crystals. Others have evolved a talent for huddling together into mats called biofilms. Many can't live at all above 50° F. It's just too hot.
Acid Life
Miles below the ocean surface on the lightless seafloor, giant cracks in the Earth's crust create sites where mineral-dense water—heated to 600° F—spews forth in roiling clouds. It's as forbidding an environment as one could imagine. Yet scientists have found hosts of organisms that have learned to thrive there.
In those circumstances, of course, photosynthesis simply isn't possible. But certain kinds of single-celled archaea have developed a unique alternative called chemosynthesis: a means of converting inorganic hydrogen sulfide dissolved from rocks into food. Archaea living on or under the seafloor make up vast microbial mats and other configurations that provide the foundation for a bizarre and abundant community of towering tube worms, gigantic clams and mussels, and strange fish and crabs that can withstand the titanic pressure and utter dark.
Laboratory studies have shown that many cold-surviving life-forms (collectively known as psychrophiles) have remarkable cellular ingredients that prevent the formation of ice crystals. Others have evolved a talent for huddling together into mats called biofilms. Many can't live at all above 50° F. It's just too hot.
Vent Life
When it comes to acidity versus alkalinity, most mammals are wimps. On the pH scale, 7 is neutral. The lower the number, the more acidic; the higher, the more alkaline. Human blood has to stay between 6.8 and 7.8 to support life. But nature is replete with creatures that thrive on the extreme ends of the pH scale.
In those circumstances, of course, photosynthesis simply isn't possible. But certain kinds of single-celled archaea have developed a unique alternative called chemosynthesis: a means of converting inorganic hydrogen sulfide dissolved from rocks into food. Archaea living on or under the seafloor make up vast microbial mats and other configurations that provide the foundation for a bizarre and abundant community of towering tube worms, gigantic clams and mussels, and strange fish and crabs that can withstand the titanic pressure and utter dark.
In Yellowstone National Park, for example, researchers took water samples and found organisms fully adapted to extremely hot acidic conditions. In California, other scientists studying the contents of mine drainage revealed incredibly tiny microbes living comfortably at a pH level as low as 0.5—the equivalent of battery acid.
On the double-digit side of the scale, soda lakes in Africa with a pH around 10 (about the same as drain unclogger) support dozens of microbial species with specially evolved chemistry that keeps the pH inside the cells neutral.
Lab studies of both acidophiles and alkalophiles continue to show the remarkable—and often unexpected—range of conditions to which life can adapt.
Location
Yellowstone: 1 ft
Sea Vents on the East Pacific Ridge: 1.5 miles
Atacama Desert, Chile: 1ft
Lake Vostok, Antarctica: 2 miles
The driest parts of Chile's Atacama high desert get rain once every few decades, and are blasted with high levels of ultraviolet radiation. These and other circumstances make the Atacama an excellent terrestrial model for conditions on Mars. Yet, extreme microbial life exists a few inches below the surface. In this image, researcher Jay Quade samples the soil for key compounds.
Credit: Julio L. Betancourt, U.S. Geological Survey
Antarctica is another site in which researchers study extreme life forms adapted to survive fiercely hostile environments. Investigators with NSF's Long-Term Ecological Research program have identified a number of novel species, including microbes (shown in scanning electron microscope inset) in lake ice from the ultra-cold Dry Valleys in East Antarctica.
Credit: Peter West, National Science Foundation; courtesy of the Priscu Research Group, Montana State University at Bozeman
Antarctica's Dry Valleys contain a number of lakes that are ice-covered year-round. Although they harbor some liquid water, their conditions are drastically different from those in temperate lakes. There is almost no circulation and the water is cut off from air and light. To see what kind of microbes might survive this environment, investigators from Montana State University lowered a sediment trap.
Credit: Courtesy of the Priscu Research Group, Montana State University at Bozeman
Researchers have removed ice cores from an ice-capped body of water called Lake Vida in Antarctica's Dry Valleys. The cores contained microbes nearly 3,000 years old, with DNA that has been extremely well preserved. Once thought to be frozen down to its bottom, Lake Vida has been shown to have a small amount of liquid water that is seven times saltier than the sea, enabling it to remain liquid at -10 C.
Credit: Courtesy of the Priscu Research Group, Montana State University at Bozeman
In the middle of East Antarctica, buried two miles beneath the surface of the massive ice sheet, is an underground freshwater lake the size of Lake Ontario. Called Lake Vostok, it may contain organisms that have been completely isolated for 500,000 years. This image, taken from ice cores obtained above the lake, reveals numerous microorganisms.
Credit: Courtesy of the Priscu Research Group, Montana State University at Bozeman
The Arctic region holds its share of extreme life forms. In this image from an expedition near Greenland, researchers remove the filter head from a pump. The device was designed to pump hundreds of liters of seawater from a given depth across a set of filters with pore sizes small enough to collect aggregates of material and associated microbes (shown in inset).
Credit: Melanie Simard; Shelly Carpenter (inset)
In the 1970s, researchers discovered that seafloor vents—cracks in the Earth's crust that release superheated water and thick clouds of minerals—are home to a host of extremophile organisms. This photo shows a typical formation. The inset photo is a scanning electron microscope image of organisms (both bacteria and archaea) inhabiting the interior of the vent chimney.
Credit: University of Washington, Center for Environmental Visualization
Researchers monitor organisms in the Colorado Rockies at one of several sites in the Alpine Microbial Observatory program. Participants study the seasonal dynamics of soil microorganisms across a wide range of elevations and geography, from mountain forests at around 9000 feet to tundra and rocky cliffs at 12,000 feet.
Credit: Ken Wilson, EBIO Department, University of Colorado
For more than 40 years, Yellowstone National Park, with its remarkable range of microenvironments, has proven to be an unflagging source for extremophile organisms. This photo shows one such environment, a geothermal spring called Black Sand Basin, named for the small granules of obsidian distributed throughout the area.
Credit: Gwendolyn E. Morgan
A scientist collects samples from Obsidian Pool, a hot spring in Yellowstone National Park that has provided investigators with a broad spectrum of extremophile diversity over the years. The genetic differences among various microbes in this environment is a subject of intense study.
Credit: Jeff Walker
This sandstone-like sample from the Norris Geyser Basin in Yellowstone National Park has a surprise occupant: A number of microbes (the greenish layer) that have learned to survive in the pores of rock that is acidic enough to dissolve nails and heated by surrounding water to about 95 F. Inset luminescence image shows microbes as pink and rock as blue.
Credit: John R. Spear; Jeff Walker (inset)
Another category of extreme microbes, called "halophiles," is adapted to high-salt conditions of the sort found in ponds of the Guerrero Negro area of Baja California, shown here. A research team from the University of Colorado, using genetic identification techniques, found a variety of novel microorganisms that thrive in this locale. The inset photo shows a piece of gypsum from the brine ponds. Each color indicates the presence of a different kind of microorganism.
Credit: John R. Spear (both)
Researchers take samples from the bubbling mud around a collapsed volcano in Russia's remote Kamchatka peninsula. The site features a remarkable diversity of extremophile activity, and is studied by scientists from around the world.
Credit: Noah Whitman,
©Exploratorium, www.exploratorium.edu
Kamchatka microbial samples, sealed in blue-topped test tubes, incubate in a hot spring among hairy-looking filamentous bacteria.
Credit: Noah Whitman,
©Exploratorium, www.exploratorium.edu
Researchers take samples from the Henderson Mine in Empire, Colorado. Among the many questions to be answered in such deep underground locations is: Are particular kinds of deep-dwelling extremophiles associated with different kinds of mineral composition in the surrounding rock?
Credit: John R. Spear
Implications
Ongoing scientific study of extremophiles is redrawing the boundaries of life and dramatically extending the known range of nature's seemingly boundless ingenuity. (Click on pictures at left to see some ramifications of that research.)
Knowledge of organisms that subsist in extremes of cold, darkness, dryness and hostile chemistry has made it possible to imagine—and even search for—life on other worlds in our solar system and beyond. At the same time, discoveries about the structure, biology and chemistry of extremophiles are leading to myriad practical applications, from medicine and pharmaceuticals to agriculture, nanotechnology and engineering. And the entire field is redefining the nature of life itself: how it arises, why it persists, and how far it can possibly go.
Europa
Research on extremophiles is suddenly making science fiction look a lot less fictional. Now that scientists have learned that certain kinds of organisms can withstand extreme cold, survive very strong doses of radiation and adapt to exotic chemical environments, it appears much more plausible that life-forms of some sort could exist on other worlds.
One promising candidate is Europa, a satellite of Jupiter shown at left. About seven-tenths the mass of Earth's moon, it is covered with water ice. That surface is riddled with cracks, and may conceal a layer of liquid water. Research in Antarctica's frozen lakes and at seafloor hydrothermal vents suggests that organisms might be able to form and even flourish in the Europan environment.
Medicine
Few people would recognize an extremophile named Thermus aquaticus, which prefers to live in water about 150 F, but it's a biotech star. That bacterium, first found in a geyser pool in Yellowstone National Park, is the source of the key enzyme (Taq polymerase) that makes DNA analysis rapid and practical. Taq polymerase does not break down at the high temperatures involved in copying DNA, allowing scientists to amplify even small samples enough to use in molecular biology, genome sequencing and DNA fingerprinting, among other uses.
Another byproduct of extremophile research is a class of compounds called
antifreeze proteins (AFPs)—first identified in the study of Antarctic fish that withstand subfreezing temperatures by inhibiting ice crystallization in cells. AFPs are now used in preserving human organs for transplant, in protecting sperm for artificial insemination, in storing food, in transporting red blood cells, and in "cryosurgery," in which target tissues are frozen.
Technology
Extremophiles employ a wide range of biochemical tricks to endure tough environments, and many of those tricks have now been incorporated into commercial products and research materials. Some of the same compounds that the microbes use to protect their cells are now used in skin-care treatments and in keeping protein and cell cultures stable in the laboratory. Enzymes modeled on extremophile chemistry are employed in detergents, and researchers are testing genetically engineered radiation-tolerant microbes as a way to break down pollutants in radioactive waste.
In another application, researchers at Montana State University determined the structure of the protective coating on super-tough viruses found in boiling acid pools in Yellowstone National Park. They have artificially replicated that structure (shown at left) for use in nanotechnology, hydrogen gas production, computer chip components, and delivery of drugs for cancer treatment.
Mars
As robots creep across the arid surface of Mars (shown at left), one of their goals is to identify potential signs of life, especially in areas that once had liquid water. But new research on Earth suggests that Martian life may not necessarily be visible at the surface. Many scientists now believe that the collective mass of all living things deep under the Earth—including microbes in fluids that circulate through the planet's crust—may exceed the total biomass on the surface.
So, if evidence of life eventually shows up, as some scientists once believed it had in a Martian meteorite found in Antarctica (inset), the results may owe a great deal to extremophile hunters right here on our home planet.
Any opinions, findings, conclusions or recommendations presented in this material are only those of the presenter grantee/researcher, author, or agency employee; and do not necessarily reflect the views of the National Science Foundation.