Two new studies add to the mounting evidence refuting the controversial claim that NASA-funded scientists had isolated a bacterium that could thrive on arsenic.

In a December 2010 paper, 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.

But in two papers published online in Science last Sunday, the findings are once more refuted. In the first study, a team from the Swiss Federal Institute of Technology in Zurich concludes that the bacteria “lacked the ability to grow in phosphorus-depleted…arsenate-containing medium,” and concludes that GFAJ-1 is “an arsenate-resistant, but still a phosphate-dependent bacterium.” In the second paper, a team from Princeton University finds that the toxin did not contribute to growth in the bacterium and was unable to find detectable traces of the substance in its DNA.

These findings echo the conclusions reached by a researcher last February, which found that trace levels of phosphorous were the cause of the reported growth in the original study.

According to a BBC article covering the story, Science has not retracted the original article, but accompanied the recent studies with the following statement:

“In conclusion, the new research shows that GFJA-1 does not break the long-held rules of life, contrary to how Wolfe-Simon had interpreted her group’s data. The scientific process is a naturally self-correcting one, as scientists attempt to replicate published results.” (Editor’s Note: One must be a subscriber to Science to read the journal’s actual statement.)

Michael New, who works for NASA’s planetary science division, issued a statement saying that the new papers “challenge some of the conclusions” of the 2010 announcement, but neither “invalidates” the original “observations of a remarkable micro-organism that can survive in a highly phosphate-poor and arsenic-rich environment toxic to many other micro-organisms. What has emerged … is an as yet incomplete picture of GFAJ-1 that clearly calls for additional research.”