It was unlikely that GFAJ-1 of the Halomonadaceae family of Gammaproteobacteria would grip the imagination; but it did. Of course, it did because instead of the long scientific name or the cryptic GFAJ-1, it was simply called Alien Life! This, of course, caused a minor sensation. It was even covered by the non-science media. The general impression left by much of the coverage was that a new form of life was discovered that uses arsenic instead of phosphorus as one of the key elements of its biochemistry. Most people know that arsenic is a lethal poison, so this finding titillated the fascination with the counterintuitive.
I’m indulging in a bit of snark. I admit the popular media is an easy target, as is our attraction to weird things that mostly turn out to be not so weird. Or, as in this case, the actual research finding isn’t as weird as it is suggestive.
The paper published online December 2, 2010 in Science [A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus] is careful not to claim much more than finding a bacteria that “…substitutes arsenic for phosphorus to sustain its growth.” In fact, what the researchers led by Felisa Wolfe-Simon did was find a strain of bacteria that normally prefers using phosphorus but could be coaxed in the laboratory into using arsenic.
Nothing wrong with that. Scientists will learn a great deal about biochemical possibilities for life from this and follow-up experiments. However, a “new life form” it is not.
Still, the bacteria do something no other form of life so far discovered can do – substitute arsenic for phosphorus into at least some of its basic metabolism. As Derek at In the Pipeline puts it, this is no trivial shift:
Phosphorus is an extremely important element for every living thing on Earth. It’s mostly found as phosphate, and phosphate groups are found all over the place: decorating proteins, carbohydrates, and lipids, as the invariable outside of DNA helices, and as the key part of the ultimate energy currency of every living cell, ATP. Phosphate’s no bit player.
This is a good time to emphasize that (as far as we can tell) all life on Earth shares the same chemistry and the same kinds of biomolecules. Humans, frogs, fruit flies, fungi, tube worms on the ocean floor, lichens in Antarctica, and weirdo single-celled creatures living in boiling hot springs: we all have cells full of proteins, carbohydrates, lipids, and nucleic acids. We use DNA and RNA to pass on our genetic information, and the enzymes we use to manipulate them and to power our cells are all similar enough that we just have to share a common ancestor. (Either that, or life only gets going in a very specific way indeed).
[Source: In the Pipeline]
The fact that GFAJ-1 can, apparently, use the arsenic molecule (technically an arsenate) in places where life usually uses phosphorus is somewhat astonishing. As the paper points out, although arsenic comes from the same group in the periodic table of elements and shares many characteristics with phosphorus – it is deceptive, biologically. It is a bigger molecule than phosphorus and has different properties. Although it can ‘fit’ into some of the same chemical locations as phosphorus, in all animals including humans, the fit is fatal. Except for GFAJ-1.
GFAJ-1 developed in an environment at the bottom of Mono Lake (California, USA) where a relatively high concentration of arsenic is present. In the natural environment, the bacterium uses phosphorus and prefers it over arsenic. However, when the scientists removed as much phosphorus as possible from the culture in which they grew GFAJ-1 and gradually increased the arsenic concentration, the bacteria were able to substitute the arsenic for phosphorus – enough so that the bacteria continued to grow and reproduce. Subsequent experiments appear to show that the arsenic was being included into DNA and possibly other metabolic elements.
What this shows is, probably, a testimony to the adaptability of life. In a specific environment GFAJ-1 has adapted enough to accept arsenic molecules for phosphorus molecules without completely disrupting its biological processes. This does not show that GFAJ-1 started as anything other than a ‘normal’ phosphorus-using form of life. It does not show that Earth had multiple chemical origins, or that life on other planets might consist of arsenic based forms. However, the research does suggest that such a form of life could exist.
Or…maybe not. In Science, reporter Elizabeth Pennisi writes that some scientists are skeptical, seeing other explanations for the results. One possible alternative is that the bacteria are actually stuffing away the arsenic in shielded bubbles in huge amounts.
I got in touch with Steven Benner [Foundation for Applied Molecular Evolution], who also proved to be a skeptic. “I do not see any simple explanation for the reported results that is broadly consistent with other information well known to chemistry,” he says. He pointed out that phosphate compounds are incredibly durable in water, but arsenate compounds fall apart quickly. It was possible that arsenate was being stabilized by yet another molecule, but that was just speculation. Benner didn’t dismiss the experiment out of hand, though, saying that it would be straightforward to do more tests on the alleged arsenic-DNA molecules to see if that’s what they really are. “The result will have sweeping consequences,” he said.
[Source: The Loom]
As Wolfe-Simon acknowledge, there at least thirty years more work to be done just with this strain of bacteria. Its use of arsenic needs to be explored from many other angles. Nevertheless, the discovery of a form of life with this capability is a direct challenge to the previous notions of biochemistry. That alone will stimulate work that only a few years ago would not have even been contemplated.