In 2010, NASA called a press conference to make one of the biggest announcements in scientific history: researchers had discovered an unusually hardy bacterium that could not only tolerate exposure to arsenic, but actually incorporate the poisonous element into its DNA. The team's findings, if correct, would have gone against some of the most widely accepted principles in science, marking a paradigm shift in the fields of biology and evolution.
Now, a year and a half later, two other teams have published findings that refute the arsenic findings outright.
The original "arseniclife" findings were published in the journal Science in 2010, by a team of researchers funded by NASA and led by Felisa Wolfe-Simon. The paper, which you can access here, reported that Wolfe-Simon and her colleagues had found a strain of bacterium in California's Mono Lake — pictured up top — capable of replacing the phosphorous in its DNA with arsenic. Phosphorus is considered one of the six essential building blocks of life, the others being oxygen, carbon, hydrogen, nitrogen and sulfur. The discovery of an organism that could eschew phosphorous in favor of another element (let alone arsenic, which is usually poisonous) would have redefined our concept of what life is, and what kinds of life are possible.
But the study's methods and conclusions — which many believed to be flimsy and insufficient — quickly triggered a torrent of criticism from scientists around the globe. Among these objectors, few proved to be as tenacious as microbiologist Rosie Redfield. For the last 19 months, Redfield has approached the arseniclife debate as an exercise in open science, cataloguing her efforts to reproduce the findings of Wolfe-Simon and her colleagues publicly on her blog. Now, Redfield's findings are reported in one of two new studies (also published in Science) that reveal GFAJ-1, while certainly bizarre, is no arsenic-swapper:
"GFAJ-1 cells growing in Mono Lake face the challenge of discriminating an essential [phosphate-containing salt] from a highly abundant but toxic [arsenic-containing mimic]," report Redfield and her colleagues. These circumstances aren't unique to bacteria living in Mono Lake, by the way. Plenty of other microorganisms face similar challenges, including "those growing in environments with scarce potassium and plentiful ammonia."
The researchers continue:
Organisms typically adapt to such conditions not by incorporating the mimic in place of the essential salt but by enriching for the salt at multiple stages... The end result is that the fundamental biopolymers conserved across all forms of life remain, in terms of chemical backbone, invariant
Tobias Erb, lead author of the second study, draws similar conclusions, noting that GFAJ-1, while arsenate-resistant, is "still a phosphate-dependent bacterium."
Taken together, the research papers refute the controversial claims published in Science just 19 months ago. "Contrary to an original report, the new research clearly shows that the bacterium, GFAJ-1, cannot substitute arsenic for phosphorus to survive," the magazine explained in a statement.
"[GFAJ-1 is] a well-adapted extremophile that lives in a high-arsenic environment," and "is likely adept at scavenging phosphate under harsh conditions, which would help to explain why it can grow even when arsenic is present within the cells."
When asked to comment, Wolfe-Simon told the AFP that the data in the newly published papers "are consistent with our original paper" and that new data is forthcoming.
"A great thing about science," she explained, "is that the ability to do rigorous tests with controls provides an increasingly accurate knowledge of life and the universe that is extremely useful.