03/30/00 BOZEMAN -- Michael Daly occasionally gets letters from schoolchildren who find "the world’s toughest bacterium" listed in the Guinness Book of World Records.
Deinococcus radiodurans can withstand 10,000 times the amount of radiation that would kill a human, earning it monikers like "Super Bug" and "Conan the Bacterium."
"It’s just phenomenal how much radiation life can take and remain viable," said Daly, a scientist at the Uniformed Services University of the Health Sciences, a military medical school in Bethesda, MD.
Daly was one of about 20 scientists who talked about their studies of "weird life," or life in extreme environments, at a recent conference near Big Sky, MT.
Sponsored by the National Aeronautics and Space Administration, the conference will help the space agency finetune programs aimed at understanding how life began in the violent early years of the planet. Those answers may help determine whether life could exist elsewhere in the universe. The gathering was organized by the Thermal Biology Institute at Montana State University-Bozeman.
"We may be the generation to understand the origins of life," said Anne Kinney, director of NASA’s Astronomical Search for Origins and Planetary Systems Program.
Recalling how Galileo’s discovery of Jupiter’s moons altered people’s world view in the 16th century, Kinney said astrobiology--or the search for life in outer space--could have a similar impact in our day.
"It comes down to, ‘Are we the center of the universe or not’," Kinney said.
On this planet, life is not limited to the cushy places. Microbes--mostly bacteria and organisms from a domain of life called archaea--live in some of the coldest, hottest, deepest, driest, saltiest, most acidic, nutrient-poor and oxygen-deprived environments scientists have thought to look.
"It’s a burgeoning field," said John Spear of the University of Colorado. "People are literally beginning to look under the rocks."
D. radiodurans was living in swollen tins of irradiated meat when discovered in Oregon in the 1950s. Studies revealed a unique, almost bizarre, ability to repair numerous DNA double strand breaks--the most lethal kind of genetic damage--within hours.
"Its DNA is highly damaged at 1.7 million rads ," Daly said. (One thousand rads is deadly to humans.) "Its DNA is all chopped up. There are between 1,000 and 2,000 DNA fragments per cell, but they’re all fixed in about 24 hours."
Engineering D. radiodurans so it also has an appetite for toxic compounds associated with nuclear waste would create an alternative (and cheaper) cleanup method for the nation’s 3,000 nuclear waste sites, Daly said. So far such work, funded by the U.S. Department of Energy, looks promising.
The potential usefulness of "extremophiles" cropped up repeatedly during the two-day meeting. After all, an enzyme isolated from a bacterium living in a Yellowstone National Park hot spring has made possible DNA fingerprinting and a host of related genetic studies and processes.
Many at the conference want to know how well the organisms they find in the planet’s meanest places are actually doing. Do they play active parts in their ecosystems or are they just hanging out? Bacteria frozen in Antarctic lake ice "barely can handle it," said MSU ecologist John Priscu, whereas microbes in hotsprings in Yellowstone National Park appear to be fairly well adapted.
"Living a poor man’s existence"is how Florida State microbiologist Imre Friedmann described microbes clinging to the underside of stones in hot dry deserts like the Atacama in Chile. A doyen of the group, Friedmann has studied extremophiles in both hot and cold environments, including the Siberian permafrost, since the 1950s.
"But only lately have I begun to understand what makes them live and die," he told the group.
Hot, dry environments are harsher than cold ones because the limiting factor is water.
"In a super-cold environment, the limiting factor is not the cold itself but the lack of warm hours," Friedmann said. "They need some heat to keep alive."
But what makes the clock stop altogether is dehydration, said James Clegg from the University of California at Davis. That is, unless you’re a microscopic invertebrate.
The embryos of brine shrimp called artemia can almost totally dry out without dying, and then rehydrate themselves when there’s water. Nematodes and an organism called tardigrade can survive nearly 98 percent dehydration.
"They’re neither dead nor alive," said Clegg, "What makes the clock go is water."
Based on the "weird life" they’ve found on earth, many of the scientists expressed plausibility for simple organisms living in outer space.
"I would not be surprised if there’s life on Mars," said Daly. "It’s not unlikely."
The issue is how to look.
Sidebar: Life on the Edge
The limits of life on Earth are much broader than previously thought. Examples of life at extreme conditions include:
Hottest: 235.4 F--bacteria from deep sea vents
Coldest: 5 F--microalgae in Antarctic rocks
Deepest: Bacteria, two miles underground in rocks
Most acidic: Unclassified organisms growing on gypsum in caves at pH 0
Highest radiation: 5 million rads--Deinococcus radiodurans (bacteria)
Saltiest: Bacteria, 30 percent salt environment
Deepest and Highest pressure: 1200 atm--at bottom of Marianas Trench (ocean)
Farthest: Moon, Streptococcus mitus (from human source) from Surveyor III camera after three years unprotected on lunar surface
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