Wednesday, July 11, 2012

Controversy over Arsenic-Loving Bacteria comes down to Data Interpretation

Mono Lake, California, home to the controversial, arsenic-tolerant
bacteria known as GFAJ-1.  Image Courtesy Flickr User anaurath (CC)

A little over a year ago, we ran a blog post about a provocative paper in the journal Science called "A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus." Or more accurately, we ran a blog post about the heated discussion and, yes, controversy surrounding the paper.

The researchers' findings were startling because they pointed to a life form--a bacterium called GFAJ-1--that, according to the authors' interpretation of the data, did not need phosphorus to survive. In fact, the authors, led by NASA astrobiology fellow Felisa Wolfe-Simon, posited that the bacteria were replacing the phosphorus in their DNA with the normally-toxic metal arsenic.

The implications were huge. If the results were reproduced by other researchers, our understanding of what makes life possible, on Earth and potentially on other planets, would need serious revision. As soon as the paper appeared online, debate raged in the scientific community. When the paper went to press a couple of months later, it was published alongside eight "technical comments" voicing concerns about the paper's conclusions as well as a rebuttal from the researchers.

Fast forward to this Monday--July 8, 2012.

Two new papers on GFAJ-1 have been published in the online version of Science, both of which suggest that the conclusions drawn in the original study were wrong. The second round of researchers--led by Tobias Erb at the Institute of Microbiology, ETH in Zurich and Marshall Louis Reaves at Princeton--took a closer look at the situation.  They grew the same bacteria (provided by the original authors) in arsenic-rich and phosphorus-depleted conditions. For the most part, their results were similar to the original study--the bacteria did indeed continue to grow in these adverse conditions, and they did find arsenic in its cells.

But when they examined the bacteria's DNA and cellular byproducts more closely, they came to different conclusions than Wolfe-Simon's team had. The new results and their revised interpretation of the data indicate that GFAJ-1 bacteria is very resistant to arsenic (a feat in and of itself), but that it does not incorporate the metal into its genetic material and that it still needs a small amount of phosphorus to survive.

So what happened?  Was the first study "bad science?"  Did the system of peer review fail?  Does this mean that we've wasted our time studying and reading about GFAJ-1?

On the contrary.  This is the process of science. This is how our understanding of the natural world grows and evolves.

In a press statement released with the new papers, the editors of Science summed it up this way:
The scientific process is a naturally self-correcting one, as scientists attempt to replicate published results. Science is pleased to publish additional information on GFAJ-1, an extraordinarily resistant organism that should be of interest for further study, particularly related to arsenic-tolerance mechanisms.


Compare the Headlines:
New York Times Story "Microbe Finds Arsenic Tasty; Redefines Life," Dec. 2, 2010

New York Times Story "Studies Rebut Finding That Arsenic May Support Life" July 8, 2012

Compare the Papers:
The Original Science Paper, "A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus" Dec. 2, 2010

The Technical Comments and Rebuttal from the authors, May 27th 2011

The New Science Papers, July 8, 2012
"GFAJ-1 Is an Arsenate-Resistant, Phosphate-Dependent Organism"

"Absence of Detectable Arsenate in DNA from Arsenate-Grown GFAJ-1 Cells"

Note: All related papers are free to access, but you may need to register with AAAS.

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