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Science

‘Arsenic life’ doesn’t live on arsenic after all, further search finds

Los Angeles Times

In a long awaited but hardly unanticipated development, two teams of scientists reported Sunday that a strange bacterium called GFAJ-1, once reported to use arsenic instead of phosphorus in its cellular machinery, requires phosphorus to grow after all — just like every other organism on Earth.

The microbe “is still a phosphate-dependent bacterium,” one of the research teams wrote in the journal Science.

The two groups’ research papers may put to rest a debate that began in December 2010 when a group of scientists, including a NASA-affiliated researcher named Felisa Wolfe-Simon, announced a jaw-dropping discovery that a strange bacterium they had discovered in California’s Mono Lake seemed to use arsenic in its cellular machinery instead of phosphorus.

That report, also published in Science, was trumpeted in the run-up to a NASA news conference as “an astrobiology finding that will impact the search for evidence of extraterrestrial life.” On the Internet, speculation circulated that the space agency had discovered aliens.

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Although little green men weren’t in the offing, the scientists’ purported discovery was considered a stunner. All life on Earth is believed to rely primarily on six elements: carbon, oxygen, hydrogen, nitrogen, phosphorus and sulfur. Finding a bacterium that substituted arsenic, which is usually poisonous, for its phosphorus might have provided scientists who ponder alien forms of life beyond Earth a new kind of life to study -- and perhaps even seek out -- on distant worlds.

But within days, outside scientists, including University of British Columbia biologist Rosie Redfield, began to question Wolfe-Simon’s results, pointing out problems in the experiment’s methods and conclusions. (Click here for further analysis from The Times.) In May 2011, Science published a collection of comments on the work, including as a response from Wolfe-Simon and her co-authors. Scientists on all sides of the debate said they would try to replicate the original results.

The research papers released Sunday, available to Science subscribers here and here, are among the fruits of that effort. Both challenged Wolfe-Simon’s conclusions, reporting that although GFAJ-1 tolerated the arsenic in its environment remarkably well, the bug did not depend on arsenic to grow.

“GFAJ-1 does not break the long-held rules of life, contrary to how Wolfe-Simon had interpreted her group’s data,” wrote Science editors in a statement accompanying the articles.

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Whether Sunday’s publications mark the end of the arsenic-life story remains to be seen. Redfield has said she’s finished working with the bacterium. The other research team wrote in its paper, and the Science editors agreed, that the molecular basis of GFAJ-1’s ability to survive in an arsenic-rich environment might merit further study.

As of 11:45 Pacific time on Sunday night, Wolfe-Simon’s website and Twitter feed made no mention of the matter. In an email exchange reported by MSNBC science writer Alan Boyle, however, Wolfe-Simon indicated that she would continue defending her work on GFAJ-1.

“There is nothing in the data of these new papers that contradicts our published data,” she wrote.


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