• DOI:10.1126/science.1218455
• Corpus ID: 20229329

GFAJ-1 Is an Arsenate-Resistant, Phosphate-Dependent Organism

@article{Erb2012GFAJ1IA,
  title={GFAJ-1 Is an Arsenate-Resistant, Phosphate-Dependent Organism},
  author={Tobias J. Erb and Patrick Kiefer and Bodo Hattendorf and Detlef G{\"u}nther and Julia A. Vorholt},
  journal={Science},
  year={2012},
  volume={337},
  pages={467 - 470}
}

• T. Erb, P. Kiefer, +2 authors J. Vorholt
• Published 27 July 2012
• Biology
• Science

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. The bacterial isolate GFAJ-1 has been proposed to substitute arsenic for phosphorus to sustain growth. We have shown that GFAJ-1 is able to grow at low phosphate concentrations (1.7 μM), even in the presence of high concentrations of arsenate (40 mM), but lacks the ability to grow in phosphorus-depleted (<0.3 μM), arsenate-containing medium. High-resolution mass spectrometry analyses revealed that phosphorylated central metabolites and phosphorylated nucleic acids predominated. A few arsenylated compounds, including C6 sugar arsenates, were detected in extracts of GFAJ-1, when GFAJ-1 was incubated with arsenate, but further experiments showed they formed abiotically. Inductively coupled plasma mass spectrometry confirmed the presence of phosphorus in nucleic acid extracts, while arsenic could not be detected and was below 1 per mil relative to phosphorus. Taken together, we conclude that GFAJ-1 is an arsenate-resistant, but still a phosphate-dependent, bacterium.