Nevermind the Arsenic

It turns out that the claims that an arsenic-based lifeform had been found were grossly exaggerated — perhaps to meet some unrealistic public expectations (to which I subscribed, I admit).

From the Philadelphia Inquirer:

Amid a flurry of criticism, a NASA-funded team on Thursday backed off the more extravagant, textbook-changing claims they’d made about a bacterium that had allegedly substituted arsenic for phosphorus in its DNA.

The original announcement, made at a NASA news conference Dec. 2, seemed to break a cardinal rule of biology that all organisms need some phosphorus to survive. NASA researchers claimed to have discovered an exotic organism in California’s Mono Lake that lived instead on arsenic, thus broadening the types of life that may exist in the universe.

On Thursday, the researchers issued a more modest claim. Instead of saying the microbes had completely substituted arsenic for phosphorus, a new statement says the arsenic replaced “a small percentage” of the phosphorus.

A number of biologists say they’ll be surprised if even this stands the test of time.

The claims “do not follow from their results,” said Simon Silver, a University of Illinois microbiologist who specializes in heavy-metal resistance in bacteria. “This conclusion is not merited from what they did and measured and I think it most likely is a mistake and should never have been claimed or published.”

The findings were published in the journal Science, which also issued the researchers’ latest statement. Most of its 16 pages were responses to critics.

At the original NASA news event, the team leader, Felisa Wolfe-Simon, had been vague about how much arsenic had substituted for phosphorus, but several times she implied that arsenic had replaced all the phosphorus in the bacterial DNA and other crucial biological molecules.

PZ Myers sums it up pretty well, too.

A good example of the need to be critical of authority, even if that authority is NASA.