The discovery of a previously unknown lifeform in California that lives on arsenic is prompting astrobiologists to broaden their hunt for alien life.
The new bacterium - GFAJ-1, part of the class Gammaproteobacteria, which also includes E.coli - was discovered in samples taken from Mono Lake. The lake is naturally high in arsenic because of its location near the volcanic hotspot of Yosemite National Park.
A NASA-funded team went looking for exotic life in the Mono Lake after they hypothesised last year that arsenic, extremely poisonous to virtually all life on Earth, could fulfill the biochemical role usually performed by phosphorus.
"We not only hypothesized that biochemical systems analogous to those known today could utilize arsenate in the equivalent biological role as phosphate, but also that such organisms could have evolved on the ancient Earth and might persist in unusual environments today," said Felisa Wolfe-Simon, the lead author of a study appearing in the journal Science Express.
Phosphates are vital to life on Earth, forming the backbone of DNA, for example. Arsenic is so toxic precisely because, being located directly below phosphorus in the periodic table, its chemical behaviour is similar: it is able to disrupt basic processes.
Astrobiologists have worked on an assumption that alien life, if it exists, is probably dependent on phosphorus too, as well as carbon, hydrogen, nitrogen, oxygen, and sulfur. The NASA team today said that view should be reconsidered in light of their find.
"This organism has dual capability. It can grow with either phosphorus or arsenic," said Professor Paul Davies of Arizona State University.
"That makes it very peculiar, though it falls short of being some form of truly 'alien' life belonging to a different tree of life with a separate origin.
"However, GFAJ-1 may be a pointer to even weirder organisms. The holy grail would be a microbe that contained no phosphorus at all."
Professor Ariel Anbar, also of Arizona State, said: "One of the guiding principles in the search for life on other planets, and of our astrobiology program, is that we should 'follow the elements'."
"[This] study teaches us that we ought to think harder about which elements to follow."
As well as greatly increasing the number of planets where life could conceivably exist, the discovery opens fundamental questions about the potential capabilities of undiscovered Earthbound organisms. ®