Scientist Smackdown: Experts Challenge Story of Arsenic-Loving Bacteria

By Andrew Moseman | December 7, 2010 4:19 pm

5-monoFirst came the extraterrestrial speculation. Then came the actual answer. Then came the backlash.

NASA’s big astrobiology news last week had nothing to do with E.T., of course—the team behind a study in Science announced the find of a kind of bacteria that appear to thrive in arsenic and can even use it in place of phosphorus in the backbone of its DNA double helix. But after the big announcement finally happened and squelched the more imaginative rumors, scientists started asking some hard questions about the study online.

Over at Slate, DISCOVER blogger Carl Zimmer rounded up expert critiques from biologists, and many didn’t hold back.

Almost unanimously, they think the NASA scientists have failed to make their case. “It would be really cool if such a bug existed,” said San Diego State University’s Forest Rohwer, a microbiologist who looks for new species of bacteria and viruses in coral reefs. But, he added, “none of the arguments are very convincing on their own.” That was about as positive as the critics could get. “This paper should not have been published,” said Shelley Copley of the University of Colorado. [Slate]

What went wrong? The critics don’t allege that the team led by Ronald Oremland is definitely incorrect on all counts; rather, most charge that the data does not prove the extraordinary claim of arsenic replacing phosphorus in the DNA.

In a guest post on the blog We, Beasties, Harvard’s Alex Bradley lays out some of the reasons:

  1. If the bacteria truly had DNA with an arsenic backbone, the arsenic would have hydrolyzed and broken down into smaller chunks when the researchers had the sample in water. It didn’t, which Bradley argues is evidence of plain old phosphorus.
  2. The phosphate concentration in the bug’s home, Mono Lake, is extremely high, meaning there’d be no selective pressure to change to arsenic.
  3. The researchers admit there was a tiny amount of phosphorus in the sample medium—2 or 3 micromolar. But Bradely argues that this small total is enough; bacteria are terribly efficient and could’ve used that amount in their DNA rather than arsenic.
  4. In conclusion, he says, “There’s a simple experiment that could resolve this debate: analyze the nucleotides directly. Show a mass spectrum of DNA sequences demonstrating that nucleotides contain arsenate instead of phosphate. This is a very simple experiment, and would be quite convincing – but it has not been performed.”

What say the study’s scientists to all this? At first, nothing—Oremland and coauthor Felisa Wolfe-Simon declared that such scientific discussions should take place in peer-reviewed literature, and refused to step into the blogosphere fracas to address any criticism. But then this afternoon, Oremland gave a rather quirky lecture on the findings at NASA headquarters  in Washington, D.C., and took questions afterward.

Oremland didn’t respond directly to all the stones hurled his way, but his talk did address a few. Regarding the phosphorus in the sample, he called it a “smidgen” and said, “It’s not enough to sustain growth. It’s very clear.” And the team didn’t do experiments like the mass spectrum because, quite simply, he said they didn’t have that much money and they wanted to get the results out there.

Indeed, Oremland’s overriding message to the critics was: We don’t mind if you question our work, that’s the way science works. And if you want to try to disprove us, go ahead—the bacteria will be made available free to researchers.

DISCOVER’s previous coverage of the Great Arsenic Announcement:
The Loom: Of Arsenic And Aliens
Bad Astronomy: NASA’s Real News: Bacteria on Earth That Lives Off Arsenic
Bad Astronomy: Snowballing Speculation Over a NASA Press Conference
Not Exactly Rocket Science: Mono Lake Bacteria Build Their DNA Using Arsenic (And No, This Isn’t About Aliens)
Gene Expression: The Alien Embargo, And Other Follies

Image: Henry Bortman

CATEGORIZED UNDER: Living World, Top Posts
  • http://clubneko.net nick

    Part of the reason folks are so hasty to jump on the critical bandwagon is that if this discovery is true, the discoverer’s names go down in history and everyone else is forgotten about. :) Also, this is likely a Nobel-prize worthy discovery, if it should prove true.

  • Think-Hank

    True that. Also, if the discovery had come from a 50-year-old male scientist, you wouldn’t be seeing this level of attack… but no, it was a lovely young lady with a pierced nose. Don’t kid yourselves about age discrimination and chauvinism — both are alive and well in the Good Ole Boy science communities.

  • scribbler

    Wouldn’t it be prudent to await the mass spec tests?

  • sciencekid

    NASA stopped being relevant along time ago.
    This is just piss poor research. Mass spectrometry is an unbelievably simple experiment, that doesn’t cost much at relative to a lot of research techniques. Such an extraordinary claim should have had some extraordinary evidence.Yet the experiment was so badly designed on so many levels, and lacks basic things like mass spec, or some other form of validation.

    Also this is being so heavily attacked because a lot of scientists hate flashy crap. Especially academic scientists, its just part of the culture to cut thru bulls***. I’ve seen world renown scientists get far worse criticism on their research, because they were trying to pull some shoddy experiments. Also Science , the journal, is like the holy grail for a lot of labs and researchers. So to see a shoddy piece of garbage get in , due to favoritism, is absolutely infuriating , I guess.

    [Moderator's note: edited the cuss word.]

  • Bob

    Why would you want the ‘results”out there, if you knew you didn’t have the money to do a proper job? Why didn’t you state that when delivering the results?

    Fame seekers should go into the entertainment business and leave science to those who do their homework.

  • Patrick

    This should be ironed out when they actually complete their research (meaning mass spectrometry of the DNA), although I, too am curious as to why they didn’t do it in the first place… we were isolating DNA and doing mass spec on all sorts of biological materials in my poorly-funded community college O. Chem class…

  • Gdawg

    #4 is close to correct, #1 and 2 way off base. It is puzzling why the authors didn’t conduct more conclusive analyses. They should have known better. There are even simpler ways than ms to prove the As or P content of DNA and the ratio of both to total nucleotide content. Expense is minor. The authors also utterly failed to acknowledge well known examples of As incorporation into a variety of biomolecules, e.g., lipids and sugars, under natural conditions as opposed to the highly artificial conditions of the reported growth experiments. The authors also failed to note that some plants hyper-accumulate As in vacuoles… which notably occurred in the +As incubations of the isolate. The bottom line is that there is no reason to expect that As is important in structural or informational macromolecules on Earth, and given the much larger cosmological abundance of P over As, no reason to expect that stony planets elsewhere in the universe are compositionally much different than Earth either.

  • J-sci

    All the criticism and shock of this work has less to do with the actual methods and claims and more to do with the quality of the peer review process used by Science Magazine and it’s editorial staff. Everyone agrees that this paper should not have gone out to press in its present form. Had this paper have been reviewed by a single competent biochemist, then the direct MS issue of DNA would have been brought up and the appropriate controls conducted. Extraordinary claims deserved extraordinary evidence. We can only conclude that a) the reviewers were derelict in their duties as subject matter experts, b) this paper was not reviewed by subject matter experts (highly possible in the exobiology field), or c) it was reviewed by subject matter experts, these issues were brought up to the editor, but the editorial staff chose to publish anyway to draw press attention and increase circulation. There is a reason why both Science and Nature have such high retraction rates.
    We should all hold judgement until someone performs the task of trying and detect nucleotide arsenate esters. If this turns out to be bunk, then the paper should be retracted. This should have been done in the first place though.

  • Photo_Guy

    Hey, do you have a source for that photo of Mono Lake you used for this? It looks mysteriously, amazingly, but perhaps coincidentally identical to one of my own.

  • http://blogs.discovermagazine.com/80beats/ Eliza Strickland

    @ Photo_Guy: It’s one of the photos that the journal Science released to the press for free use. The image’s copyright is “2010 Henry Bortman.”

    – Eliza, DISCOVER online news editor

  • http://wycieczki-szkolne.internet24h.mazowsze.pl/a/wedding-photography-essex,47765 wedding photography essex

    I have not checked in here for some time since I thought it was getting boring, but the last several posts are good quality so I guess I will add you back to my everyday bloglist. You deserve it friend :)

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