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NASA's secret is finally out: Researchers say they've forced microbes from a gnarly California lake to become arsenic-gobbling aliens. It may not be as thrilling as discovering life on Titan, but the claim is so radical that some chemists aren't yet ready to believe it.
If the claim holds up, it would lend weight to the idea that life as we know it isn't the only way life could develop. Organisms with truly alien biochemistry could conceivably arise on a faraway exoplanet, or on the Saturnian moon Titan, or even here on Earth.
"Our findings are a reminder that life as we know it could be much more flexible than we generally assume or can imagine," Felisa Wolfe-Simon, an astrobiology researcher at the U.S. Geological Survey, said in a statement from Arizona State University announcing the results. Wolfe-Simon is the lead author of a paper reporting the findings, which was published online today by the journal Science.
Four years ago, while studying at ASU, Wolfe-Simon proposed that some organisms in extreme environments might be adapted to use arsenic in place of phosphorus. Phosphorus is one of the elements essential to life's chemistry -- in addition to carbon, hydrogen, nitrogen, oxygen and sulfur. Arsenic, which is just below phosphorus on the periodic table, is poisonous precisely because it can take phosphorus' place in biomolecules.
"It gets in there and sort of gums up the works of our biochemical machinery," ASU's Ariel Anbar, a co-author of the Science paper, explained.
In search of arsenophiles
Wolfe-Simon theorized that some organisms could have evolved in ancient times to make use of arsenic-based compounds known as arsenates, in place of the phosphates used by virtually all the organisms we know today. Such arsenophiles might even persist in environments with elevated levels of arsenic -- environments such as the hydrothermal vents at the bottom of the ocean, or Mono Lake in California.
It turns out that that eerie-looking tourist destination, 13 miles east of Yosemite National Park, contains arsenic as well as the usual phosphorus. Wolfe-Simon and her colleagues designed an experiment to take a particular type of salt-loving bacteria called GFAJ-1 from Mono Lake's mud sediments, wean it off phosphorus, and see if it could switch its diet to arsenic.
In the paper published today, the researchers report that some of the bacteria could survive on arsenic and incorporate it into their cellular biochemistry. Instead of the usual phosphate-rich DNA, they observed arsenate-rich DNA. Heightened levels of arsenic also showed up in the cell's proteins and fats. The scientists used mass spectroscopy, radioactive labeling and X-ray fluorescence to confirm that the arsenic was really being used in the biomolecules rather than merely contaminating the cells.
If that could happen in the laboratory, why couldn't it happen naturally? ASU astrobiologist Paul Davies, another one of the paper's co-authors, has long held that "weird life" -- based on chemical building blocks unlike our own -- could exist right under our noses on Earth, or in extraterrestrial environments.
"This organism has dual capability," Davies said in today's announcement. "It can grow with either phosphorus or arsenic. That makes it very peculiar, though it falls short of being some form of truly 'alien' life belonging to a different tree of life with a separate origin. However, GFAJ-1 may be a pointer to even weirder organisms. The holy grail would be a microbe that contained no phosphorus at all."
Davies said GFAJ-1 was "surely the tip of a big iceberg" -- and Wolfe-Simon agreed.
"If something here on Earth can do something so unexpected, what else can life do that we haven't seen yet?" she asked. "Now is the time to find out."
Some bet that it's wrong
Some scientists said they were impressed by the measures that Wolfe-Simon and her colleagues took to verify their findings. "The organization of the experiments presents convincing and exhaustive results," Milva Pepi, an environmental microbiologist at the University of Siena, was quoted as saying in a Science news report.
But Steven Benner, an astrobiologist at the Foundation for Applied Molecular Evolution, told me he was unconvinced. He was invited to Washington today to lay out the skeptical view during a much-hyped news conference at NASA Headquarters. "I'm the guy they bring in to throw the wet blanket over all the enthusiasm," he joked.
He was impressed by the finding that bacteria could get by with so little phosphorus and so much arsenic, but he questioned the conclusion that the arsenic was truly taking the place of phosphorus. Benner explained that chemists have long been familiar with the properties of arsenate compounds. "We know, for example, that they fall apart in water quickly," he said. "Those structures are not going to survive in water."
In their paper, Wolfe-Simon and her colleagues say that the GFAJ-1 bacteria can apparently cope with that instability, perhaps because of intracellular mechanisms that keep water out. Benner, however, said that other scientists would have to first confirm that the arsenic is really being taken up the way the paper describes, and then figure out how the process squares with what's already known about biochemistry.
"If this result is true, we've got to go back and rewrite a lot of chemistry," Benner said.
Benner is willing to put his money where his mouth is: "I've wagered Felisa $100 that that's not arseno-DNA," he told me.
That being said, Benner acknowledged that arsenic could conceivably play a role in sustaining truly alien life. "If I'm going to go to Mars, where the temperature is lower, and water is scarcer, and arsenate esters are more stable, this is something I might look for," he observed.
Hype vs. reality
The paper published today could be regarded as the latest chapter in a discussion that's been going on for years among astrobiologists. Wolfe-Simon, Davies and Anbar telegraphed their hypothesis almost two years ago in a paper titled "Did Nature Also Choose Arsenic?" In another paper, Wolfe-Simon speculated that arsenic-based life could exist on Mars or one of the moons of Jupiter or Saturn. And in June, a different group of researchers reported results hinting at the possibility of an alternate biochemistry on Titan, one of Saturn's moons.
So when NASA announced that Wolfe-Simon and other astrobiologists were gathering in Washington today to discuss results that could "impact the search for evidence of extraterrestrial life," speculation ran rampant. Some journalists, including yours truly, could deduce what the news conference was about and read the study in advance -- but only on the condition that nothing referencing the research would be published until Science lifted its embargo. Othersfiguredout that the revelations had to do with arsenic and Mono Lake, even without getting an advance peek at the paper.
Still others took wild guesses about the subject of the news conference. Had NASA detected arsenic on Titan? Was there evidence of extraterrestrial biology at work?
"Some of the coverage has been almost comically erroneous," Ginger Pinholster, director of public programs at the American Association for the Advancement of Science, told Space.com. The AAAS is the publisher of the journal Science, and Pinholster is in charge of the operation that distributes the journal's papers in advance.
Here's a video about the research that was done up by the AAAS:
The whole idea behind the embargo system is that journalists have a chance to digest publications, ask questions and put the research in perspective before they publish their articles. The system isn't perfect -- as NASA and Science found out in August when embargoed research about a bizarre planetary system was outed on Twitter an hour before the scheduled release. And some make the argument that the system is too elitist for the Internet age.
I'm in favor of embargoes -- in part because it helps avoid precisely the kind of hype that was engendered by NASA's public announcement about the news conference. In fact, I'd argue that such announcements should be governed by the same embargo, to head off the cycle of hype and disappointment that some of you may be going through this week. There's also the advantage that you can almost immediately check the original research paper if you so choose.
The scientific search for evidence of life beyond Earth isn't as fast-paced as a science-fiction plotline -- and maybe that part of the story is as important as the news about arsenic in the old lake. But what do you think? Are you disappointed? Intrigued? Bugged by the hype, or bugged by the current system for publishing scientific research? Feel free to chime in with your comments below.
Update for 5:35 p.m. ET: This afternoon's NASA news conference served to lay out the case for (and against) arsenic-based life, and one of the high points came when Wolfe-Simon and Benner sparred over how much arsenic might have been incorporated into the bacteria's biological machinery. Here are other highlights:
- Wolfe-Simon gave a tour de force explanation of her results, including a jazzy computer-generated video showing arsenic atoms replacing phosphorus atoms in a DNA chain. We're offering the video just above. Give it a click.
- Benner brought a couple of lengths of heavy chain links to represent molecular chains, as well as a twisted-up ring of aluminum foil to represent the arsenic. The message underlying the props was that arsenic compounds would be too weak to bind molecular chains together for a long time before breaking.
- Pamela Conrad, a researcher at NASA's Goddard Space Flight Center who specializes in Martian astrobiology, said the Science result was "delightful because it makes me have to expand my notion of what environmental constitutents might enable habitability." If high levels of arsenic as well as organic molecules were found by future Mars probes -- for example, NASA's Curiosity rover, which is due for launch next year -- "you could begin to put a picture together about what the environmental chemistry might portend," Conrad said.
- The biggest OMG moment came when Mary Voytek, head of NASA's Astrobiology Program, referred to a classic "Star Trek" episode in which the Enterprise crew confronted a seemingly menacing creature called a Horta. "This is, in our mind, the equivalent of finding that Horta, which was silicon-based life, substituting carbon -- which is what we think all life forms are made of -- with silicon. Now we're talking about an organism that we think ... is replacing phosphorus with arsenic," she said. "This is a huge deal."
Science lifted its embargo on the research paper, "A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus," shortly after noon ET today. The AAAS said the embargo was lifted because "news reports disclosing the findings in the paper are now appearing online."
In addition to Wolfe-Simon, Davies and Anbar, authors include Jodi Switzer Blum, Thomas R. Kulp, Gwyneth W. Gordon, Shelley E. Hoeft, Jennifer Pett-Ridge, John F. Stoltz, Samuel M. Webb, Peter K. Weber and Ronald S. Oremland. The study was funded in part by NASA's Astrobiology Program. Wolfe-Simon, Anbar, Davies and Oremland are members of the NASA Astrobiology Institute "Follow the Elements" team at Arizona State University.