Did NASA screw the pooch again?
If you’ve been anywhere on earth the past week (aside from living next to a hydrothermal vent without access to the internet), you have undoubtedly learned that NASA scientists have discovered a bacterium that they claim uses arsenic instead of phosphorous in its DNA.
In ordinary living things (in fact, in all known living things before this announcement), the “backbone” of DNA–the structure that holds the “bases” that make up the genetic code–consists of alternating phosphates and sugars. NASA announced that the newly discovered bacterium GFAJ-1, which was discovered in the arsenic rich Mono Lake in Yosemite National Park, uses arsenic rather than phosphorous in the backbone, which supposedly thus alternates sugars with arsenates. This claim is superficially plausible, mainly because arsenic occupies the same “column” on the periodic table, and thus bonds in many ways similar to phosphate. But more important than the plausibility was the incredible temptation to proclaim that a “new” way to construct DNA thus made life elsewhere in the universe that much more likely. (It’s not obvious to me why elsewhere in the universe it is more likely that arsenic would be available and phosphorous not, nor why alternate life form theories weren’t more plausible when they assumed a genetic code other than one depending on the long and delicate DNA molecules.)
NASA has been pushing extraterrestrial life for a long time. I hesitate to suggest an impure motive for it, mainly because you can think it up yourself. But just to give another example of a less than conclusive claim they pushed, take the Australian chert from Mars claimed by NASA scientists in the August 16, 1996 issue of Science to have microfossils, not consistent with contamination from Earth sources. While they continue to push that claim, nobody else seems much excited anymore about it, although it to was proclaimed at a live news conference and made its way across the new media and (the much smaller then) internet.
Nevertheless last week NASA scientists again called a news conference to announce this latest discovery. The paper, with a sexy roll out entitled “What Poison? Bacterium Uses Arsenic to Build DNA and Other Molecules” (abstract; article behind paywall) as well as a podcast, is in the December 3, 2010 issue of Science: Felisa Wolf-Simon, et al., “A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus” (abstract; article behind paywall). (This may not be the best place to make this observation, but why are papers by government scientists not made freely available? I’m not asking that they be deprived of all the fruit of their labors, but they are not getting paid for appearing in Science anyway. Why should we have to pay that journal for science we paid for in taxes?)
Of course, with all that hoopla, you would expect it to get all sorts of publicity. And it did. Not all scientists fail to grasp the mechanics of modern PR. So newspapers all over the world, including a special report in the New York Times–with a headline that combines both cute and pompous: “Microbe Finds Arsenic Tasty; Redefines Life“–as well as popular science magazines and science blogs all trumpeted the discovery and its shattering importance for days.
The problem is that it is looking like the claim is not well supported. Newsweek, the science part of which seems to have it out for NASA claims of this sort, has collected quotes from the naysayers in “Arsenic and New Life–Or Not” by Sharon Begley (December 8, 2010). There are some pretty scathing criticisms of the paper in that article. This appears to be the price you have to pay when you try to work PR systems outside peer-reviewed journals. I urge you to read the claims yourself, which to me appear to be quite convincing. Alexander S. Bradley, Agouron Institute Fellow at Harvard University, is quoted in the article as saying flat out:
“the claim is almost certainly wrong.” The scientists overlooked evidence that “the DNA in question actually has a phosphate—not an arsenate—backbone,” he says: an arsenate DNA backbone hydrolyzes (falls apart) in water within minutes, yet during a multi-step chemical procedure the Mono Lake DNA, despite being in water for an hour or two, the DNA backbone held up fine. “Any arsenate-DNA would have been quickly hydrolyzed in the water, breaking down into fragments of small size, [but] phosphate-DNA would not hydrolyze quickly, and large-sized fragments might be recoverable. So what size are the fragments of DNA extracted from GFAJ-1? They are large … If this DNA did not hydrolyze in water during the long extraction process, then it doesn’t have an arsenate backbone. It has a phosphate backbone. It is normal DNA.”
You can read even more scathing criticism of the research in the article. More doubts are raised in the blog of Professor Rosie Redfield and the comments thereto, which contains a very detailed explanation of their experimental methods. It’s beginning to look like that chert from Mars didn’t have any bacteria with arsenate-deoxyribonucleic acid.
Will we see any follow-up by the Times or others? Of course not. Science journalism is about making splashes, not providing a record of the state of science. Sports “journalists” provide more critical examinations of accepted wisdom than science journalists.