The astounding flexibility of life

This week’s big news is undoubtedly the discovery of a bacterium that can (if forced to) use arsenic in place of phosphorus.  Though it’s being hyped as “completely different from any life on Earth”, it was in fact isolated from Mono Lake; an unusual environment, certainly, but not an extraterrestrial one.  The work was, however, funded by NASA’s astrobiology division, who are interested in making sure that if we ever do find an alien life form we have a broad enough view of what life is to recognize it.   The surprise here is not that the bacterium can survive in the presence of high concentrations of arsenic — many organisms can do that — but that it appears to incorporate arsenates into the structure of nucleic acids, proteins and lipids, where phosphates would normally be.  This was not previously believed to be possible, since arsenates react much more rapidly than phosphates — up to a million times more rapidly — and this would seem to pose problems (for example) in maintaining the information content of DNA.

There’s no data yet about how this bacterium, which is dubbed GFAJ-1, manages to maintain its vital functions, or indeed how well it does it.  I’d guess that if arsenates are really being used in the structure of DNA, this might result in a very rapid mutation rate.  The authors comment that GFAJ-1 clearly prefers growing on phosphorus-containing medium to growing on arsenic alone.  Too bad; from now on, arsenic is what it’s getting.

Update: check out xkcd’s take on the news coverage on this story.

Update 2: Here’s a detailed and skeptical review of the paper, which makes some excellent points.

Update 3: Oh, dear, NASA doesn’t seem to be handling criticism well.  A shame.

Wolfe-Simon, F, Blum, JS, Kulp, TR, Gordon, GW, Hoeft, SE, Pett-Ridge, J, Stolz, JF, Webb, SM, Weber, PK, Davies, PCW, Anbar, AD, & Oremland, RS (2010). A bacterium that can grow by using arsenic instead of phosphorus Science : DOI: 10.1126/science.1197258