Bacterium uses arsenic in DNA

[asterroc]

NASA's big press release today was that a new form of DNA was discovered in a type of bacteria living in Mono Lake, California. DNA usually requires phosphorus to hold together the different "rungs" of the "ladder". On the periodic table of the elements, phosphorus falls directly above arsenic, meaning they have the same number of electrons in their outer shells, and therefore act similarly in forming molecules. This is the very reason that arsenic is well-known as a poison: it is easily incorporated into human (or animal, or plant) chemistry, it replaces the phosphorus, but it does a crappier job than phosphorus and even though it can form similar molecules they easily fall apart.

Apparently this bacterium has not only overcome that - there are many bacteria that can live in an arsenic-rich environment - but it even uses that fact. This bacterium can apparently switch between using phosphorus, and using arsenic, depending upon which is available in its environment.

NASA press release

A very slightly more technical article, including a description of tests used to determine that the arsenic is actually incorporated into the DNA.

And a couple blog posts, one from a science writer Ed Yong, one from astronomer-turned-science-writer Phil Plait.

Comments

[seekingferret.livejournal.com]

Dear lord, I hope we wouldn't have ruled out looking for life anywhere with high concentrations of arsenic before this. Just because our form of DNA can't work with arsenic doesn't mean a life form without DNA and/or with an entirely different sort of chemistry might not function in a high arsenic environment.

[zandperl.livejournal.com]

FWIW we do not currently have the technical ability to determine if any particular body has life. We need to be able to distinguish the spectrum of a planet from that of its star, and this is currently far beyond our capabilities for the vast majority of exoplanets that have been discovered, and barely beyond our capabilities for the few planets (I forget how many, but it's in the single digits) that we have been able to resolve separately from their stars. If we did have the ability, it's my understanding that we would be looking for an oxygen-rich environment and that the presence of oxygen is currently our main criterion for life. Yes I know that's limiting us to detecting plant-like life, but if we don't even know what other life forms are like, we certainly don't have any other criteria to detect them.

[seekingferret.livejournal.com]

You're limiting your 'we', as if the scientific establishment were a monolith, which is sometimes an excusable mistake. Certainly another important criteria for life, which isn't biology-dependent, is the organization of information. So some scientists are looking for signs of life using radio astronomy.

The presence of abundant Oxygen is a reasonable criterion to look for not merely because of its presence and significance to our own existences on Earth but because our knowledge of stellar chemistry tells us it's unusual to find in another star system, so we reason based on our limited experience that its presence is a good clue to investigate further. Needless to say, it's no kind of proof at all of any kind of life, and if we detected a planet rich in both oxygen and arsenic, as I said in my last post, I should hope we wouldn't have ruled it out as a candidate on the basis of its high arsenic level.

[zandperl.livejournal.com]

You're right that information organization is "platform" independent. However, that limits us to a much more narrow section of life, in that it can only detect intelligent life forms that choose to communicate using radio waves. While it is a reasonable criterion as well, I think it is even more limiting than looking for planets with oxygen. However, the criterion of radio communications is currently a lot easier for us to search using.

And yeah, I hope you're right that if we found a planet with oxygen and lots of arsenic that we didn't just drop it and stop studying it. In reality we would probably continue to study it but not expect to find life.