yeah, about those arsenic-absorbing microbes…

December 8, 2010

Science writer Carl Zimmer has been talking to scientists about NASA’s study of arsenic loving microbes and what he’s been hearing isn’t good. In fact, the microbiologists asked to comment on the paper even used the term flim-flam to describe what they think of it, and at least one expert in the field is drafting an official letter to Science, the journal which published the findings. Now, we’ve already discussed the big problems in the media’s notion that scientists discovered arsenic-based life on Earth, but since I’m not a biologist, I had to wait for some input from the professionals to dig a little deeper and figure out why so many of them were very lukewarm to the supposedly big news. Turns out that the biggest problem with the study is that it really hasn’t demonstrated what it claimed, and that data presented to show that arsenic was being used in the microbes’ DNA and RNA molecules was based on very indirect inference rather than solid, demonstrable evidence.

Here’s a basic summation of the problems as the opining microbiologists see them. First, there just weren’t enough controls in the experiment to really check if the surviving bacteria weren’t adapting to use arsenic but actually scavenged phosphorous from their dead brethren. Secondly, when the bacteria were broken down to their constituent macromolecules and analyzed with a mass spectrometer, the high arsenic content was in a category of molecules that the investigators associated with DNA and RNA, but which weren’t necessarily the only things those molecules could’ve been. There’s no question that the high levels of arsenic were seeping into the microbes’ cellular machinery, but where it ended up is definitely a subject of debate since the paper’s data leaves a lot of room for uncertainty. Hopefully we’ll see another experiment on these extermophiles, one conducted with more rigor and better controls, but until then, microbiologists will be taking their complaints to the academic media, where the researchers who conducted the study said they’ll be answering their critics. I suppose that’s the proper way to do things, but at the same time, it would’ve been nice to see a lively scientific back and forth in the news rather than the typical scientists-say-blank pronouncements.

Of course one important thing to note here is that arsenic-based life, or living things that use arsenic, may still be out there and microbiologists are by no means ruling out the possibility of their existence. It’s just that the paper from NASA’s researchers doesn’t offer sufficient proof that it was actually found. We have a hypothetical framework for a number of living things with exotic chemistry, like the hydrogen-breathing and ethane-using microbes we hope live on Titan, but until we find that these strange creatures really exist in the wild, we won’t leave the realm of speculation when wondering what chemicals can sustain alien life. My experience tells me that a lot of people reading about this microbiological debate will just sigh and say "there go those scientists, always trying to deflate some new discovery," when in fact they’re just asking for more rigor and better quality data before someone announces a new kind of life to the world at large. And really, that’s why peer review is a crucial part of the scientific process. It’s intended to keep hype in check and make sure that big claims come with solid data to back them. Though in this case, it seems that the prestige of the space agency might have outweighed the objections of the reviewers, if any of them were microbiologists…

[ illustration by Hau Si Yuan Julian ]

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  • Paul

    While the “OMFG aliens!!11!” hype before the announcement was ridiculous, I think the criticism of the research has been just pathetic.

    For example, one of the main critics, Norman Pace (U. Colorado) berated Wolfe-Simon for not ruling out the bugs extracting phosphorus from the growth medium, not the arsenic. Ignoring that she did exactly that in the original paper, using bacteria in growth medium alone as a control for the in-phosphorus and in-arsenic tests.

    Felisa Wolfe-Simon:“In the Science paper, we show data from one experiment of many replicated experiments that demonstrates no growth of cells in media without added arsenate or phosphate (Figure 1). These data clearly demonstrate that strain GFAJ-1 was unable to utilize the 3┬ÁM P to support further growth in the absence of arsenate.”

    Meanwhile, the critic, Pace, was asked if he’d allow/encourage his students to replicate the work he has been so vocally critical of. Response, “Of course not. There’s no point, it’s stupid.”

    One of these people is doing science, the other is being just a dick.