Tuesday, December 7, 2010

Arsenic-Based Life? Just Add Water.

Barely a week after announcing the discovery of a bacteria from California’s Mono Lake a group of NASA-funded and –associated scientists insist incorporate arsenic compounds, rather than phosphorous compounds, into their DNA and other cell structures – thus broadening our view of conditions conducive to life – others in the field are shaking their fingers at the science.

Read it here at Slate.com.

To sum up: The scientists Slate spoke to don’t deny that arsenic-based life could exist, they merely challenge what they call sloppy methodology in the NASA experiments that don’t take into account that arsenic is much more prone than phosphorous to dissolve in water – leaving arsenic-based DNA in tatters, rather than the chunks the scientists identified – along with the fact that some of the salts fed to the bacteria were “contaminated” with phosphorous, thus not eliminating the possibility that the bugs merely “eked out” an existence on the available phosphorous rather than substituting the arsenic.

I don’t pretend to understand the intricacies of the science, but I’ve always loved a good flim-flam story, especially when those accused of the flim-flammery retreat rather than address the criticism. Rosie Redfield, a microbiology researcher at the University of British Columbia and one of the experts quoted by Slate does what I assume is an admirable job of taking apart NASA’s research here. Another explanation of the phosphorous/arsenic in water trick can be found here, written by Harvard microbiologist Alex Bradley (I found this one a bit more accessible to my layman brain).

What I appreciate about the approach the critics are taking is that they’re not saying, “Oh no. Arsenic-based life can’ exist.” Because they’re scientists, they want to look at the evidence before they reach any conclusions. What they are saying is that the methodology used in the NASA paper doesn’t prove that these Mono Lake bacteria are arsenic-based life forms. Bradley sums it up pretty well by saying that even in the absence of esoteric biochemical processes which could keep arsenic-based DNA from dissolving in water:
In the absence of biochemistry, pure chemistry takes over: any arsenate-DNA would have been quickly hydrolyzed in the water, breaking down into fragments of small size. Alternatively, phosphate-DNA would not hydrolyze quickly, and large-sized fragments might be recoverable.
Slate’s story is worth reading for the explanation of the science, as well as to see how quick some scientists are to announce Earth-shattering news and then equally as quick to hide behind peer-review procedurals when their science is called into question. Carl Zimmer, writing for slate, quotes Jonathan Eisen of UC-Davis as saying:
If they say they will not address the responses except in journals, that is absurd. They carried out science by press release and press conference. Whether they were right or not in their claims, they are now hypocritical if they say that the only response should be in the scientific literature.
It does seem odd to me to use the penny press to announce your news, then scurry behind the peer-review structure when the critics come out – and you knew the critics would come. So I’ll be watching this with much interest.

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