New Study Contradicts Controversial Arsenic Finding

New Study Contradicts Controversial Arsenic Finding

Last week, one of the main critics of a NASA-funded study that claimed the discovery of a life-form that could thrive on arsenic, announced results that contradict the original conclusions, dealing the latest blow to the controversial finding.

In December 2010, a team led by NASA astrobiology research fellow Felisa Wolfe-Simon announced that a microbe dubbed GFAJ-1 could thrive in the presence of arsenic, incorporating the toxic substance in its DNA in the place of phosphorous, one of the six elements of life. The results were made public in a NASA press conference that drew attention to the finding’s implications on the agency’s quest for life in other parts of the universe.

Yet many scientists were not convinced. Ensuing debate prompted sharp criticisms, several of which were published in Science as technical comments along with the print version of the article on June 3, 2011. Many of the comments centered on a concern that phosphorous contamination could account for the bacteria’s growth – not the level of arsenic.

This is what Rosemary Redfield, a microbiologist at the University of British Columbia in Vancouver, Canada, set out to investigate.

In a posting last week on, an electronic preprint archive, Redfield announced her results after looking at the two main arguments of the paper: that the bacterium had managed to grow in low phosphorous and high arsenic conditions, and that arsenic had been incorporated into the organism’s DNA.  Consistent with criticisms faulting contamination in the original study, Redfield found that the bacterium’s growth could be accounted for as a result of trace levels of phosphorous. Measuring samples with and without added arsenic, but with the same level of phosphorous, Redfield found growth rates equivalent to those described in the original study.

A collaboration with Leonid Kruglyak from Princeton University allowed Redfield to analyze the bacterium’s DNA in high-arsenic conditions. “The results showed that there is no detectable arsenic in the DNA,” she told CBS News.  Although this suggests that more sensitive measurements could potentially detect the presence of arsenic, Redfield’s first result counters the original study’s main claim: that the bacterium could grow on arsenic alone.

In a ScienceInsider article covering the story, Redfield says: “We can do fancier analyses that push the limits of detection down, but I think the burden of proof is back on the authors. They are going to have to provide some better data than they did in their paper,” she said.

ScienceInsider reported that Wolfe-Simon and her colleagues declined to comment on the new study until it is published. They added, however, that they only suggested arsenic was in the DNA and that the key point of the paper was that the microbe was able to use the toxin to grow. The article quotes John Tainer, a biochemist who recently joined Wolfe-Simon’s team, in saying: “What this is about is refuting an extreme interpretation of the paper.” This is a shift in the team’s original position, as discussed in the 2010 press conference, that when measuring the arsenic concentration in the organism, they found it to be behaving as phosphorous would: as the backbone of the DNA.

Redfield has submitted her findings to Science for publication.

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