Phil Nye, The Science Guy blogs at the Planetary Society website about NASA's announcement of microbes that can substitute arsenic for phosphorus:
If you or I ingest arsenic, well... it doesn't go so well. If you are, on the other hand, a certain species of bacterium from Mono Lake, California, ingesting this seemingly toxic metal is simple enough. You would have a way to use arsenic in the place of phosphorus -- not just in some chemical reactions, but in your very DNA, the instructions for living. Felisa Wolfe-Simon, a NASA Astrobiology Research Fellow, and her colleagues have found that a bacterium from the Halomonadace ae family of proteobacteria is able to completely swap arsenic for phosphorus.
Note that arsenic is immediately below phosphorus on the Periodic Table of the Elements. Perhaps you remember the silicon-based creature called horta in the original Star Trek series. The idea was that silicon is right below carbon in the periodic table; they are in the same chemical period. While swapping silicon for carbon is probably not a possibility, this is the same concept -- except that it's science, not science fiction. Arsenic is highly toxic to living things like us, but, chemically, it behaves in a similar way to phosphate.
Who knows what other organisms are right under our noses that have perhaps taken it yet another step? They might not even use DNA at all. They could be an entirely different type of life. If these arsenic-lovers can be discovered in such a well-researched lake, who knows what else is out there, on our world or somewhere far, far away? This kind of research is an adventure. It helps us appreciate the remarkable nature of life on Earth. It helps us know our place in space. We at the Planetary Society will keep searching and encourage people everywhere to support this kind of research.
Phil Plait, The Bad Astronomer anticipated the NASA announcement. He updated his post after this afternoon's press conference:
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). 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.
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.
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