The organism, GFAJ-1, was cultured and discovered by Felisa Wolfe-Simon, a NASA astrobiology fellow in residence at the US Geologic Survey in Menlo Park, California. The organism was isolated and cultured beginning in 2009 from sediments she and her colleagues collected along the shore of Mono Lake, California, U.S.A. Mono Lake is hypersaline and highly alkaline. It also has one of the highest natural concentrations of arsenic in the world. The discovery was widely publicized on December 2, 2010.
On the tree of life, according to the results of 16S rRNA sequencing, the rod-shaped GFAJ-1 nestles in among other salt-loving bacteria in the family Halomonadaceae. Many of these bacteria are known to be able to tolerate high levels of arsenic, but GFAJ-1 can go a step further. When starved of phosphorus, it can instead incorporate arsenic into its DNA and continue growing. By introducing radioactive arsenic into the growth medium of some of the microbes, Wolfe-Simon learned that approximately one-tenth of the arsenic absorbed by the bacteria ended up in their nucleic acids. Within the DNA extracted from GFAJ-1 cells starved of phosphorus, arsenic bonded to oxygen and carbon in the same way phosphorus bonds to oxygen and carbon in normal DNA, and found that when cultured in arsenate solution it grew 60% as fast as it did in phosphate solution — not as well, but still robustly.
When the researchers added radio-labelled arsenate to the solution to track its distribution, they found that arsenic was present in the cellular fractions containing the bacterium's proteins, lipids and metabolites such as ATP and glucose, as well as in the nucleic acids that made up its DNA and RNA.
A critic has suggested that perhaps the trace contaminants in the growth medium used by Wolfe-Simon in her lab cultures are sufficient to supply the phosphorus needed for the cells' DNA. He thinks it's more likely that arsenic is being used elsewhere in the cells. What is needed next is to know which molecules in the cell have arsenic in them, and whether these molecules are active and functional.