Transmission electron micrograph shows a strain of the arsenic-eating bacterium called GFAJ-1.
Credit: Credit: Science/AAAS.
Scientists haven't yet found E.T., but the discovery of an Earth microbe that thrives on arsenic should greatly broaden the search for life beyond Earth, NASA announced today (Dec. 2).
In a much-anticipated press conference, NASA announced that the bacterium GFAJ-1, found in a briny California lake, doesn't just tolerate arsenic ? it can incorporate the poisonous stuff into its DNA and other vital molecules in place of the usual phosphorus.
"We've cracked open the door to what's possible for life elsewhere in the universe," said study lead author Felisa Wolfe-Simon, NASA astrobiology research fellow at the U.S. Geological Survey in Menlo Park, Calif. "What else might we find? What else might we want to look for?"
NASA sent out alerts for the conference on Monday (Nov. 29), setting the Internet abuzz with speculation and rumors that life beyond Earth had been found, perhaps on Titan, Saturn's largest moon. The actual discovery ? which is very much terrestrial ? falls short of those expectations, dashing the hopes of some who may have let their imaginations run wild.
"I'm sorry if they're disappointed," Mary Voytek, director of NASA's astrobiology program, told reporters today. "But this is a huge deal. This is a phenomenal finding."
Science fact looks like fiction
Scientists had regarded phosphorus as one of six key ingredients ? along with carbon, hydrogen, nitrogen, oxygen and sulfur ? that all life on Earth needs to survive.
So finding a microbe that substitutes arsenic for phosphorus is like coming face to face with the fictional Horta beast from the science-fiction TV show "Star Trek," one of the scientists said. The Horta was based on silicon rather than carbon.
"In our mind, this is the equivalent," Voytek said. "It will fundamentally change the way we define life, and perhaps the way we look for it."
Search for extraterrestrial life
In particular, scientists hunting for life on Titan, Mars and other bodies throughout the solar system and beyond should open their minds, according to researchers. For if some life-forms on Earth are doing something so radically different, who knows what alien life might look like? [The Weirdest Life on Earth]
"The implication is that we still don't know everything there is to know about what may make a habitable environment," said astrobiologist Pamela Conrad of NASA's Goddard Space Flight Center in Greenbelt, Md. "It opens up our perspective."
The discovery also stresses that researchers shouldn't focus narrowly on looking for signatures of certain molecules, Conrad added. Rather, they should assess a variety of variables at any particular site.
As an example, arsenic may be a more likely life ingredient than phosphorus in certain environments, such as Titan, researchers said. Titan is so cold ? temperatures average minus 290 degrees Fahrenheit (minus 179 degrees Celsius) ? that stable molecules like phosphate might not be reactive enough to help generate or sustain life.
Phosphate, a molecule composed of phosphorus and oxygen, is a key ingredient in the DNA of "normal" life. In the weird bacterium, the much more unstable arsenate apparently can take its place.
On Titan, "you might well want to have the increased reactivity of arsenate," said biochemist Steven Benner of the Foundation for Applied Molecular Evolution in Gainesville, Fla., during the press conference.
Benner made the skeptic's case against the new discovery, saying he thinks arsenate is likely too unstable to have been truly incorporated into the bacterium's DNA.
A second genesis?
The arsenic-munching bacterium can utilize phosphorus as well as arsenic. In fact, it grows faster when given phosphorus. So it's probably just extremely adaptable, not a life-form so fundamentally different as to belong to an entirely separate tree of life, researchers said.
But such organisms may be out there, waiting to be found. If such a "shadow biosphere" exists ? if life has truly evolved more than once on Earth ? that implies that life isn't so special, that it can take root fairly easily. So the odds of life existing elsewhere in the universe would shoot up.
That's just speculation ? for now. The study does open scientists' eyes to new possibilities, suggesting that life can assume more various forms ? and live in a wider variety of places ? than previously thought, researchers said.
So it's important to make sure life-hunting
probes are flexible ? able to explore many different environments and to look
for many different molecules, researchers said. That way, future probes could
reduce the chances of overlooking evidence of alien life simply because it
appears in a form that is completely unexpected.
"You would hate to go somewhere and not find it," Conrad said.
- Arsenic-Eating Bacteria Open New Possibilities for Alien Life
- Extremophiles: World's Weirdest Life, California's Mono Lake
- How Does Arsenic Kill?
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