STEVE INSKEEP, Host:
A new discovery by NASA could mean that someday we might find life in places we had never thought to look, both on Earth and on other planets. The discovery is a bacterium that does what no organism is supposed to be able to do. It may be able to do without one of the elements considered essential for life. Instead of that element, it uses a deadly poison - arsenic. NPR's Jon Hamilton tells us more.
JON HAMILTON: The discovery comes from a young astrobiologist at NASA who likes to find exceptions to rules. Felisa Wolfe-Simon says she was fascinated by crustaceans because they don't use iron to carry oxygen around their bodies the way most species do. Instead, they substitute copper. And Wolfe-Simon thought this sort of chemical substitution might go even further.
D: What about the main building blocks of life - carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur? Can we substitute any of those? And the dogma is no.
HAMILTON: That's because all known forms of life need those six elements. But Wolfe-Simon started thinking about phosphorus and the element just below it on the periodic table - arsenic.
D: Arsenic is toxic because it looks like phosphorus. So your cells and my cells and microbial cells can't tell the difference.
HAMILTON: Until they try to actually use arsenic, and die. Still, she thought, evolution has produced an incredibly wide range of organisms, including ones that thrive on substances that are usually poisonous.
D: So I wondered, could it be possible here on Earth that we might actually be able to find something? So we hedged our bets and we went to an arsenic-rich environment where the natural experiment may have been set up.
HAMILTON: The arsenic-rich environment she picked was Mono Lake in California. It's a very odd lake - very salty, full of arsenic. And yet it's teeming with life, including lots of microscopic organisms in the muddy lake bed.
D: We went out to Mono Lake and gathered some mud. Put that mud in a broth or a liquid, where I've added a lot of arsenic and no phosphorus.
HAMILTON: The idea was that only an organism that could live on arsenic would survive. She says in retrospect the experiment was pretty bold.
D: As a young scientist I thought, well, why not do this? The chances of it working are low. But if it works, it's very profound. So I took a sample and microscopically examined the sample of these test tubes, and sure enough, there were fast-swimming little bugs in there.
HAMILTON: NASA officials lost no time hailing the result at a press conference in Washington. Mary Voytek directs the agency's astrobiology program.
D: This is a phenomenal finding. We are talking about taking the fundamental building blocks of life and replacing one of them with another compound.
HAMILTON: And that has implications for NASA's ongoing search for signs of life elsewhere in the universe. Pamela Conrad, an astrobiologist at NASA's Goddard Space Flight Center, says it could even affect the agency's work on Mars.
D: So for example, on Mars Science Laboratory, if you had an environment that appeared to be rich in arsenic or some unanticipated metal, and you also had a finding of organic molecules, you could begin to put a picture together about what the environmental chemistry might portend.
HAMILTON: Jon Hamilton, NPR News.
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