Comment on "A bacterium that can grow by using arsenic instead of phosphorus".

Wolfe-Simon et al. (Research Articles, 3 June 2011, p. 1163; published online 2 December 2010) reported that bacterium GFAJ-1 can grow by using arsenic instead of phosphorus. However, the presence of contaminating phosphate in the growth medium, as well as the omission of important DNA purification steps, cast doubt on the authors' conclusion that arsenic can substitute for phosphorus in the nucleic acids of this organism.