Life That Thrives on Arsenic? Not So Fast

NGC 3603.

It was the talk of space scientists at the time. In 2010, a young researcher, Felisa Wolfe-Simon, published a paper in the journal Science, reporting that she and her colleagues had found bacteria in Mono Lake, Calif., that could be made to live on arsenic. Yes, arsenic - the poison.

"Not only did this microbe cope," said Wolfe-Simon, a NASA astrobiology research fellow at the U.S. Geological Survey, "but it grew and thrived. And that was amazing." The microbe was called GFAJ-1.

But now Science has published two papers saying she was wrong - that the Mono Lake bacteria weren't using arsenic compounds at all, but instead phosphorus, a very common building block of living things.

"We conclude that GFAJ-1 is an arsenate-resistant, but still a phosphate-dependent bacterium," wrote Tobias Erb and several fellow microbiologists in Zurich.

Wolfe-Simon's paper drew international attention because - if correct - it potentially broadened the definition of life as we know it, including life on other planets. Might there be arsenic-based life on Mars, or among the moons of Jupiter, that space probes were missing? Could arsenic be in the DNA of alien cells? Living things, for all their complexity, are based on six elements: oxygen, carbon, hydrogen, nitrogen, phosphorus and sulfur. Arsenic has chemical similarities to phosphorus, but it's toxic.

So the original Wolfe-Simon paper was explosive. But so was the response. Rosie Redfield of the University of British Columbia in Canada quickly answered with a blog post: "Basically, it doesn't present ANY convincing evidence that arsenic has been incorporated into DNA (or any other biological molecule)."

Redfield was a co-author of one of the new papers. She and colleagues at Princeton University analyzed the work of Wolfe-Simon's team, and found it wanting. "Mass spectrometry showed that this DNA contains only trace amounts of free arsenate and no detectable covalently bound arsenate," they concluded.

Wolfe-Simon, in an email to ABC News, said, "There is nothing in the data of these new papers that contradicts our published data, which is also consistent with our current results. Our work continues to build upon our finding of extreme resistance to arsenate toxicity and the unexpected uptake of arsenate in the GFAJ-1 cells in the absence of added phosphate."

In other words, the search for life as we know it, for now, is back to where it was.