NASA's real news: bacterium on Earth that lives off arsenic!

The entire universe in blog form
Dec. 2 2010 11:12 AM

NASA's real news: bacterium on Earth that lives off arsenic!

[UPDATE (Dec. 7): The research outlined below is under very heavy fire from other biologists. I've written a follow-up post about it.]

[Update (13:30 MT Dec. 2): I misunderstood a part of this research dealing with arsenic when I read the journal paper, which was made more clear during the press conference. I have corrected the relevant text below, and struck through the old text. Hope this doesn't confuse anyone, and sorry about that!]

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  


NASA scientists announced today an incredible find: a form of microbe that apparently evolved the ability to use otherwise toxic arsenic in their biochemistry!

First off, just to be straight and to dispel the rumors: this is not aliens on Titan, or Mars, or anywhere else. This bizarre life form was found right here on good ol' Earth. And don't be disappointed: this is still pretty cool news.

Here are the critters in question:


Note the scale; a typical human hair is 100 times thicker than these beasties.

DM blogger Ed Yong of Not Exactly Rocket Science has written an in-depth and detailed account of all this as well. Highly recommended!

The bacteria (technically, the strain GFAJ-1 of Halomonadaceae) was found in Mono Lake, an extremely alkaline and salty lake in California near the Nevada border. And I do mean salty and alkaline: it has about twice the salt of ocean water, and has the incredible pH of 10 (neutral water has a pH of 7, and the pH scale is logarithmic; this means the lake water has the same alkaline strength as commercial antacids). Worse yet, the lake has a high concentration of arsenic, a deadly poison to many forms of life (including us). This makes the water toxic for most living creatures as we know them; for example there are no fish in the lake. However, there are algae, shrimp, and other such flora and fauna.

... including these new microbes. Dr. Felise Wolfe-Simon found them in the mud around the lake, and discovered that not only do they happily live with the arsenic that when subjected to high levels of arsenic in their environment, they actually incorporated it into their biochemistry!

Life like us uses a handful of basic elements in the majority of its biochemistry: carbon, hydrogen, oxygen, and nitrogen for the most part. But phosphorus is also a critical element in two major ways: it's used as the backbone of the long, spiral-shaped DNA and RNA molecules (think of it as the winding support structure for a spiral staircase and you'll get the picture), and it's part of the energy transport mechanism for cells in the form of ATP (adenosine triphosphate). Without it, our cells would literally not be able to reproduce, and we'd be dead anyway if it were gone. There are many other ways phosphorus is used as well, including in cell membranes, bones, and so on. It's a key element for all forms of life.

Oh, pardon me: all known forms of life up until now. In many ways phosphorus is chemically similar to arsenic (the latter is right below the former in the table of elements, a clear sign of chemical companionship). In fact, in very small amounts (and I mean like 50 parts per billion) arsenic may be important for life, but in larger amounts it's incredibly toxic -- there's a terrifying litany of such attributes.

But these microbes in Mono Lake, at some point in their evolution, decided that if you can't lick 'em, join 'em. They have somehow been able to utilize arsenic in the lake, using it instead of phosphorus in their biochemistry. To determine this, Dr. Wolfe-Simon took samples of the microbes, adding more and more arsenic while decreasing the amount of phosphorus in their environment to essentially zero. This would kill almost everything known to man, yet these little critters thrived. Even weirder, the bacteria were able to survive when either the phosphorus or the arsenic was reduced, but not both. So somehow, it's able to use both of these elements as needed to survive.

Amazingly, using radioisotope-tagged molecules containing arsenic, they were able to find that the microbes incorporated the arsenic into their very DNA! It's hard to stress how shocking this is; as I understand it, saying something like that to a microbiologist without evidence would've had them slowly backing away from you and looking for weapons or an escape route.

That is seriously freaky. So what does this mean in the scale of things?

For one thing, it means that life, as Jeff Goldblum so eloquently stated in "Jurassic Park", will find a way. It's not clear at all how these bacteria were able to figure out how to utilize arsenic, but it's not hard to imagine that understanding this will have all sorts of implications for biology, and perhaps even medicine.

And for another, it means that we need to be a little more open-minded when it comes to looking for life on other worlds. If a strain of bacterium this truly and awesomely bizarre can be right here under our noses -- in California, for frak's sake! -- then what the heck will we find on other planets?



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