The backbone of standard DNA (the blue spiral ribbon-like structure in this drawing) contains an alternating chain of linked phosphate and sugar molecules. Strong evidence indicates that in GFAJ-1 the phosphate is replaced by arsenate.
Today, NASA scientists reported the discovery of a bacterium that can grow by using arsenic instead of phosphorus, most notably for making nucleic acids, in an article in the journal Science (Science DOI: 10.1126/ science.1197258).
The organism in question is a bacterium, GFAJ-1, cultured by Wolfe-Simon from sediments she and her colleagues collected along the shore of Mono Lake, California. Mono Lake is hypersaline and highly alkaline. It also has one of the highest natural concentrations of arsenic in the world.
Image of GFAJ-1 grown on arsenic. Image Credit: Jodi Switzer Blum
GFAJ-1 is apparently most closely related to the salt-loving bacteria in the genus Halomonas. Many of these bacteria are known to be able to tolerate high levels of arsenic. But unlike its relatives, when starved of phosphorus, GFAJ-1 can instead incorporate arsenic into its DNA and continue growing as though nothing remarkable had happened.
Image of GFAJ-1 grown on phosphorus. Image Credit: Jodi Switzer Blum
Paul Davies, the director of BEYOND: Center for Fundamental Concepts in Science at Arizona State University in Tempe, Arizona, said:
It is the first time in the history of biology that there’s been anything found that can use one of the different elements in the basic structure. . . . [Wolfe-Simon’s finding] can only reinforce people’s belief that life can exist under a much wider range of environments than hitherto believed. . . . [The discovery of GFAF-1 is] the beginning of what promises to be a whole new field of microbiology.
Professor Olsen @ Large 
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