It appears the general public weren’t the only ones feeling let down after NASA’s press conference last week. Following last Monday's vague announcement that a major astrobiological breakthrough would be discussed on Thursday, many speculated that perhaps NASA had found evidence of extraterrestrial life.
No dice — rather, NASA announced that a group of researchers headed by astrobiologist Felisa Wolfe-Simon had discovered a microbe, GFAJ-1, capable of substituting arsenic for phosphorus in its DNA, proteins and lipids. In a post over the weekend, I explained how this microbe could change what we previously considered science fiction into scientific fact.
But in order for this sea change to occur the science supporting Wolfe-Simon's conclusions needs to be solid, and now some are suggesting it isn't.
After taking the time to review the data, which was published last week in Science (paywalled), many members of the scientific community have qualms with Wolfe-Simon’s work. Carl Zimmer runs down their criticisms over at Slate.
Some scientists take issue with the techniques used or the precision (or apparent lack thereof) with which those techniques were executed. For example, in order to prove that GFAJ-1 was capable of surviving on arsenic alone, the microbe was grown in an environment that was high in arsenic but lacked phosphorus. However, Wolfe-Simon admits that her team couldn't remove all of the phosphorus (a result of "trace impurities" in the salts that were added to the environment for the experiments).
Therefore, some scientists have suggested, perhaps GFAJ-1 wasn’t really incorporating arsenic into its biomolecules as a means to survive; maybe it was living off of scraps of phosphorous instead. These aren't the only points of skepticism: Some researchers don't think that Wolfe-Simon’s DNA purification techniques were appropriate, while others feel that certain figures in the paper are misleading.
Rather than completely disregarding the findings published in the Science article, I would much rather label them as preliminary. At first glance the article does appear a bit skimpy: It lacks sections detailing the methods or discussing the results presented. And the authors outline all of their methods and data in a short two and a half pages, and much of that discussion is spent justifying assumptions that were made during the experimental design and data analysis stages of their work. This could imply that more data needs to be gathered or different techniques should be employed in order to construct a more cohesive argument.
There is, however, one particularly compelling piece of data that supports the researchers' claims: When GFAJ-1 is cultured in an environment that lacks both arsenic and phosphorus (but which does contain trace amounts of phosphorous as a result of the aforementioned salts), its cells do not grow. This damages the argument that the trace phosphorus in the supposedly "phosphorus free" conditions is enough to sustain GFAJ-1.
Normally many more follow-up experiments would be required before this work would go to press — and I can only speculate as to how this article was published. Perhaps the editors at Science felt that the implications of the work were so groundbreaking that any available information should be published ASAP. Perhaps some of Wolfe-Simon’s competitors were also getting close to publication so the group rushed to publish the data they had. Or maybe, as the Slate article suggests, a press-starved NASA pushed to the forefront a finding that wasn't quite ready for prime time.
Whatever the reason, the concerns raised in the scientific community over this research are not cause to completely abandon the idea that an organism could be sustained by arsenic. And we'll know soon enough, because after such a strong response to the original finding, there's little doubt that multiple research groups will be inspired to take up this project and attempt to replicate Wolfe-Simon's findings. The questions at stake — What are organisms made of? What are the limits of adaptation and what does that say about the evolution of life on Earth and possibly elsewhere? — are too fundamental to leave unanswered.
Emily Staudenmaier is a Neurobiology Research Assistant and Laboratory Manager at Brandeis University. She has a B.A. in Molecular Biology from Kenyon College.