Web edition: December 7, 2010
The news that NASA scientists coerced a microbe to incorporate a form of arsenic into its cells in the place of phosphorus made a big splash December 2, sending waves far beyond the shores of Mono Lake.
Speculation about the findings raged even before the paper came out. NASA’s cryptic press release, sent out a few days earlier, stated that the new findings would “impact the search for evidence of extraterrestrial life.”
Then the paper, in Science, was released. It revealed that researchers had found a microbe in California’s Mono Lake and cultured it in the lab. They starved the critter of phosphate, a chemical building block that is found in DNA and is also a crucial player in the metabolism of all living things. Instead of phosphate, the team force-fed the bacterium a form of arsenic. Various detection and analytical techniques suggested that the critter started using arsenate as a building block in phosphate’s place.
Two waves of discussion ensued: one lambasted much of the media’s coverage, another lambasting the findings themselves. On December 3, microbiologist Rosie Redfield of the University of British Columbia took the Science paper apart in her blog.
Redfield’s detailed critique concludes: “Bottom line: Lots of flim-flam, but very little reliable information.… There’s a difference between controls done to genuinely test your hypothesis and those done when you just want to show that your hypothesis is true. The authors have done some of the latter, but not the former.”
Other scientists also piped in. At We Beasties, guest blogger Alex Bradley, a Harvard scientist who studies the chemical and molecular evolution of life, raised concerns similar to Redfield’s. And science writer Carl Zimmer, blogging at Slate, stated that of the dozen scientists he reached out to, “almost unanimously, they think the NASA scientists have failed to make their case.”
The main criticism stems from the lack of conclusive evidence about where any arsenate that the microbes took in actually ended up. And the research team didn’t do (or didn’t report) on controls or experiments that would have made the results more watertight.
Nonetheless, most scientists don’t dismiss the notion that such a microbe could be out there. A 2007 National Academies of Sciences report calls for research on arsenic-based life, a mandate based on studies done long before the current work.
Fortunately, the story doesn’t end here. As noted by one reader on Zimmer’s blog:
“This is why I love science (and why I work as a researcher). When someone publishes a paper (good, bad or in between), other scientists from all over the world pick up on it and then if they don't believe the hype ... they set about trying to reproduce the study.…”
Stay tuned. Those experiments, and new ones, will certainly follow.
R. Ehrenberg. Bacterium grows with arsenic. Science News Online. December 2, 2010. Available online: