Absence of Detectable Arsenate in DNA from Arsenate-Grown GFAJ-1 Cells
Resisting Arsenic The discovery of a bacterium living in the extreme conditions of Mono Lake, California, created a major controversy because it was claimed to be able to grow solely on arsenic and could substitute arsenate for phosphate in its key macromolecules, including DNA. Working with the same Halomonas spp. bacterium, known as GFAJ-1, and ultrapure reagents, Erb et al. (p. 467) found that the bacterium needed a low level of phosphate (1.6 µM) to grow at all. Rather than significant specific arsenic incorporation, when the organism was grown in 40 mM arsenic, its nucleic acids acquired a trace of arsenic. Similarly, Reaves et al. (p. 470) found that GFAJ-1 could not grow in the absence of phosphate and, moreover, that its growth was not stimulated by the addition of arsenate, although a trace amount of arsenic was also detected in DNA. Thus, GFAJ-1 shows no particular facility to substitute arsenic for phosphate, when phosphate is limiting, but it can tolerate high concentrations of the poison while efficiently scavenging phosphate. Claims of arsenic substitution for phosphorus in the biomolecules of a Mono Lake bacterium are not independently reproduced. A strain of Halomonas bacteria, GFAJ-1, has been claimed to be able to use arsenate as a nutrient when phosphate is limiting and to specifically incorporate arsenic into its DNA in place of phosphorus. However, we have found that arsenate does not contribute to growth of GFAJ-1 when phosphate is limiting and that DNA purified from cells grown with limiting phosphate and abundant arsenate does not exhibit the spontaneous hydrolysis expected of arsenate ester bonds. Furthermore, mass spectrometry showed that this DNA contains only trace amounts of free arsenate and no detectable covalently bound arsenate.