As You Like It

An arsenic-eating bacterium showcases some of modern science's greatest strengths, but also some key weaknesses.

What a week to be a bacterium, or to have friends who are bacteria.

It all started with this press release: "NASA will hold a news conference at 2 p.m. EST on Thursday, Dec. 2, to discuss an astrobiology finding that will impact the search for evidence of extraterrestrial life. Astrobiology is the study of the origin, evolution, distribution, and future of life in the universe."

Astrobiology research covers a lot of different topics, and if you think about it, NASA’s definition doesn't preclude looking into life right here on our very own planet. But I think people who are not so familiar with the field can be forgiven for reading those lines, first taking “astrobiology” to mean “visitors with green skin," and then seeing the search for evidence of extraterrestrial life as confirmation of this belief. And so, in the days between Monday (when the press conference was announced) and Thursday (the press conference day), there was some intense speculation about what NASA had actually discovered.

Cue Thursday, and word starts to spread beforehand that we're not dealing with off-planet life after all. Instead, it's a newly discovered bacterium (GFAJ-1, henceforth “Gufajwon”) from Mono Lake in California, which the authors of the study (warning: paywall) claim is not only able to survive at high arsenic concentrations, like many bugs we already know about, but is able to replace one of life's favourite elements, phosphorous, with nasty, nasty arsenic, in all sorts of important places including in its genome.

Because the genome is made of DNA, and DNA is a polymer with four different constituents, it's handy to write genomic sequences as strings of A, C, G, and T, but there's a lot of repeating structure needed to hold the whole thing together. In particular, each letter needs to be attached to the next with a phosphate bond, so in fact it would be more precise to write a DNA strand as “ApGpGpCpA.” What we're talking about, then, is an organism that prefers to build “ApGpGpCpA,” but can change to “AasGasGasCasA,” and if it has to, it guesses. That's still pretty exciting, especially since arsenic-based DNA should typically fall apart in minutes.

This is a very interesting discovery, and worth telling the world about. The great thing about Google News is that you can easily get pages and pages of headlines that aim to communicate the significance of this work to the general public. Sadly, some of these missed the mark by a co(s)mically wide margin. For example:

“NASA Discovers Arsenic-Based Life Form.” Not exactly. An arsenic-based life form would prefer arsenic to phosphorous, possibly to the point of having no use whatsoever for phosphorous. But the paper clearly shows – and the authors are upfront about this – that feeding Gufajwon an exclusive diet of arsenic yields the microbial equivalent of that in Super Size Me: a big, bloated, insufferable bacterium that is desperately trying to find a place for all this junk you keep feeding it. Variants on the “arsenic-based” theme (“thrives on arsenic,” “could totally demolish a big bag of arsenic right now,” etc.) are equally inaccurate.

“Are Aliens Among Us?” Yes, this bacterium is American; no, a birth certificate will not be forthcoming.