NASA's arsenic microbe science slammed
A recent high-profile astrobiology discovery led by a NASA scientist is being called into question by a B.C. microbiologist, who says the science was sloppy.
"I don't know whether the authors are just bad scientists or whether they're unscrupulously pushing NASA's 'There's life in outer space!' agenda," wrote University of British Columbia Prof. Rosie Redfield on her blog about the study, which was published Dec. 2 in Science.
Rosie Redfield is one of a number of scientists in different fields who have publicly criticized the arsenic microbe study since it was published online on Dec. 2.
Alex Bradley, a biogeochemist, posted his own review of the work on the science blog We, Beasties, writing that a "subtle but critical piece of evidence has been overlooked." Bradley cited Steve Benner, a distinguished fellow at the Foundation for Applied Molecular Evolution in Gainesville, Fla., who said during a NASA news conference that DNA-like arsenic compounds are very unstable and tend to break down within minutes when exposed to water.
Consequently, arsenic-based DNA should break down into small pieces during its chemical analysis, Bradley said.
The fact that the DNA fragments isolated in the recent study were very large demonstrates that they were normal DNA made with phosphorus, not arsenic, he added.
In a blog post over the weekend, Redfield described the study led by astrobiologist Felisa Wolfe-Simon as "lots of flim-flam, but very little reliable information."
Wolfe-Simon and her colleagues reported that a microbe found in California can use arsenic — an element that is usually toxic to living things — instead of phosphorus to make chemical building blocks of life such as DNA, proteins and fats. The bacteria were grown in an environment with very high arsenic and almost no phosphorus.
The discovery was hailed as "something different than life as we knew it." NASA scientists said it opened the possibility of finding life in parts of the universe that might otherwise be considered uninhabitable.
Redfield dissected Wolfe-Simon's molecular biology and microbiology methods and results in detail on her blog, RRResearch, garnering tens of thousands of hits and dozens of comments from other scientists.
One of the key findings of the NASA study was that the microbe's DNA was partly made of arsenic instead of phosphorus, based on chemical analyses.
Cleanliness, calculations criticized
But Redfield disagreed, writing that the paper "doesn't present ANY convincing evidence that arsenic has been incorporated into DNA (or any other biological molecule).
In an interview Monday, Redfield said the methods used by the researchers were so crude that any arsenic they detected was likely from contamination. There is no indication that the researchers purified the DNA to remove arsenic that might have been sticking to the outside of the DNA or the gel the DNA was embedded in, she added. Normally, purifying the DNA is a standard step, Redfield said: "It's a kit, it costs $2, it takes 10 minutes."
She also questioned why the researchers analyzed the DNA while it was still in the gel, making the results more difficult to interpret: "No molecular biologist would ever do that."
Redfield also disagreed with the paper's conclusion that the bacteria had to rely on arsenic to build molecules such as DNA because there wasn't enough phosphate (a form of phosphorus) available in the samples with the lowest levels. Her arithmetic showed that in fact, there was enough phosphate to account for the amount of bacteria that grew.
"That shocked me," she said.
Redfield added that there was actually very little arsenic in the DNA of bacteria grown in an environment high in arsenic and low in phosphorus. In fact, the amount was only twice that of the cells grown without arsenic: "That's a level of difference that could be easily explained by very minor contamination."
Debate shouldn't be in media: NASA
When NASA spokesman Dwayne Brown was asked about public criticisms of the paper in the blogosphere, he noted that the article was peer-reviewed and published in one of the most prestigious scientific journals. He added that Wolfe-Simon will not be responding to individual criticisms, as the agency doesn't feel it is appropriate to debate the science using the media and bloggers. Instead, it believes that should be done in scientific publications.
Redfield said the reason she posted the review on her blog is partly because scientific publications such as Science — and the debates therein — are typically behind a paywall and inaccessible to the public.
"I blog openly…to bring this stuff more into the open where everybody can see it," she said.
However, encouraged by some of the commenters on her blog, Redfield is drafting a shorter version of the post to submit to Science, which the authors of the original paper will have a chance to respond to.
Redfield acknowledged that the original paper was peer reviewed, but said that fact was "a puzzle." She suggested that perhaps the reviewers may not have had an expertise in microbiology. Another possibility is that the reviewers raised some concerns, but the editors of Science didn't think they were serious or were "motivated by the coup of getting this very high-profile article."
But she said ultimately, no one can know what actually happened during the review process: "All we can do is judge what has been published."