Earth Chemistry Earth Chemistry
Canadian research disproves arsenic-based DNA
By Tyler Irving
Posted September 2012
The discovery of a bacterium that can use arsenic instead of phosphorus to construct its DNA is ‘flim-flam.’ That’s according to University of British Columbia microbiologist Rosie Redfield, who this summer published what she says is the final word on the controversy that has come to be known by its Twitter hashtag, #arseniclife.
In December 2010, Felisa Wolfe-Simon and her colleagues at the NASA Astrobiology Institute and the U.S. Geological Survey published a paper in Science reporting on a new organism isolated from arsenic-rich Mono Lake in California. Called GFAJ-1, it grew on artificial media that contained high levels of arsenic and very low levels of phosphorus. Secondary ion mass spectrometry (SIMS) appeared to show arsenic associated with its DNA.
Days after the publication, Redfield posted a rebuttal on her blog. Among her many objections was the claim that there wasn’t enough phosphate for growth. “If you starve bacteria for phosphate, they can be very economical with it,” says Redfield. “My calculations suggested there was just enough phosphate to explain the amount of growth they saw.” Others joined in the fray, pointing out that the arsenate ester bonds that would be required to make arsenic-based DNA are unstable in water, with an estimated half-life of less than one second.
Despite these concerns, the original authors continued to insist that their results were valid and did not retract the paper. Redfield then decided to solicit help in trying to replicate the findings herself. In her latest paper, also published in Science, her team used stringent DNA purification protocols that weren’t followed by the original authors. The arsenic disappeared, indicating it wasn’t covalently bound to DNA. Moreover, the purified DNA was stable in water for months, something that wouldn’t be true of an arsenic-based molecule.
For Redfield, the latest publication marks the end of the story. Still, she would have preferred to see a retraction of the original paper. “When researchers publish things that are not true, they should be apologising for them,” she says. “I don’t think anybody has apologised.”
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