Molecular analysis based on 16S rRNA sequences shows GFAJ-1 to be closely related to other moderate halophile ("salt-loving") bacteria of the family Halomonadaceae. Although the authors produced a cladogram in which the strain is nested among members of Halomonas, including H. alkaliphila and H. venusta, they did not explicitly assign the strain to that genus. Many bacteria are known to be able to tolerate high levels of arsenic, and to have a proclivity to take it up into their cells. However, GFAJ-1 was controversially proposed to go a step further; when starved of phosphorus, it was proposed to instead incorporate arsenic into its metabolites and macromolecules and continue growing.
The sequence of the genome of the bacterium GFAJ-1 is now posted in GenBank.