Felisa Wolfe-Simon and colleagues reported last week in Science, the discovery of a microbe in Mono Lake, California, USA, that uses arsenic to build its genetic material. The team used nanosecondary ion mass spectrometry (NanoSIMS) and inductively coupled plasma mass spectrometry to measure the relative concentrations of arsenic in microbial cells grown under various conditions.
The results showed similarities in the distribution of arsenic and the distribution of iron and zinc. The distribution of phosphorus did not match the distribution of the other elements, suggesting that arsenic had replaced phosphorus in the bacteria’s cellular material. X-ray studies revealed oxygen and carbon were the nearest neighbors to As, at distances that were consistent with bond lengths.
Since the report, these finding have been questioned by the scientific community. The suggestion is that, while the mass spectrometry results provide valuable data, the technique is destructive so no conclusions about the chemical environment of As can be drawn. Similarly, the extended X-ray absorption fine structure spectroscopy technique used does not provide direct proof that the arsenic is incorporated in the DNA backbone. Only X-ray crystallography or NMR of isolated molecules can conclusively prove this.
Steven Benner, Foundation for Applied Molecular Evolution, USA, notes that arsenic-based esters, necessary for DNA formation, decompose in water in minutes. He believes this would make their inclusion into DNA chemically difficult, but he acknowledges that there is currently no simple explanation for the data presented and joins the growing number of researchers calling for more rigorous characterization of the microbes.
To stimulate further discussion and aid research, Science is making the paper freely available for a two-week period and the team have agreed to provide samples of their bacterial strain for external testing.
- A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus
F. Wolfe-Simon, J. Switzer Blum, T. R. Kulp, G. W. Gordon, S. E. Hoeft et al.,
- Arsenic Bacteria Breed Backlash
Chemical & Engineering News, Accessed 9/12/2010