849.Studies Rebut Finding That Arsenic May Support Life

How science works.

By The Associated Press, The New York Times, July 9, 2012


It was a provocative finding. Strange bacteria in a California lake thrived on something completely unexpected: arsenic. What it suggested was that a very different kind of life could exist — possibly on some other planet.

The research, supported by NASA and published by the journal Science in 2010, led to widespread speculation that life might exist elsewhere, along with sharp dissents about the finding.

Now Science has released two papers that it says repudiate the original research. They “clearly show” that the bacteria cannot use arsenic as the researchers claimed, the journal said in an accompanying statement.

The original paper, based on research led by Felisa Wolfe-Simon of NASA’s Astrobiology Institute, said bacteria found at Mono Lake in eastern California could grow by substituting arsenic for phosphorus. Phosphorus is considered essential to life; arsenic, while chemically similar, is a poison.

If the bacteria can break the rules like this, the speculation went, who knows what kinds of life may be possible beyond our planet?

But the paper has long been an object of skepticism; last year Science published a number of challenges from other scientists.

For both new papers, scientists did their own tests of the bacteria. One team, led by Rosemary Redfield of the University of British Columbia, reports that arsenic does not contribute to the growth of the bacteria. They suggest that the original results may have been skewed by an undetected contaminant in the arsenic the researchers used.

The other paper, from Swiss researchers, finds the bacteria highly resistant to the poisonous effects of arsenic but still dependent on phosphorus; in the original experiment, trace contamination with phosphorus may have allowed the bacteria to grow.

Dr. Wolfe-Simon, who is now at Lawrence Berkeley National Laboratory, said she stood by her research.

In an e-mail to The Associated Press, she wrote, “There is nothing in the data of these new papers that contradicts our published data,” and added that her team continued to build on its original finding.