The arsenic bacteria story has taken a new turn. First, Wolfe-Simon et al. published a paper in Science in December of last year, accompanied by much hoopla, reporting that they'd grown bacteria in a low phosphorus environment, and that the bacteria were able to incorporate arsenic in place of the missing phosphorus in their DNA. The research was funded by NASA, so much of the hoopla had to do with these results proving that extraterrestrial life was possible.
We, as many others, blogged about the story at the time, and a few times since, including here. We were skeptical, but not nearly as skeptical or vociferous as many other critics. And we were skeptical not about the biochemistry, though it seems we should have been -- our excuse is that it's not our field -- but about whether the results, if true, meant what was being claimed they meant about evolution. We thought not.
We didn't follow all the online discussion, and there was a lot of it, but perhaps the most meticulous critic was Rosie Redfield, a microbiologist at the University of British Columbia. Almost immediately upon publication of the Wolfe-Simon paper she went into much detail on her blog about what was missing, not controlled for, or misinterpreted by Wolfe-Simon et al., and she and Wolfe-Simon had a back and forth, also on her blog, addressing some of Redfield's questions. The basic issues were that there was enough phosphorus in the growth medium, even if limited, to allow bacteria to grow, and that Wolfe-Simon et al. hadn't conclusively demonstrated that arsenic in fact had been incorporated into the bacterial DNA, much less that life could exist on it alone. Redfield also questioned the purity of Wolfe-Simon's samples.
In May, Science published eight technical comments about the original paper, to which the original authors responded. Redfield was one of those eight. Wolfe-Simon offered to send samples of her GFAJ-1 bacteria to anyone who wanted to test her results, and Redfield said she might be interested.
And she was. She is now replicating the original experiments, but correcting the numerous errors she pointed out in her critiques. And, she's blogging her experience and her results as they come. So far, she has grown the bacteria in a phosphorus-deficient medium, without added arsenic, and found that they do grow, albeit slowly, apparently contradicting Wolfe-Simon et al. She has confirmed through sequencing that she's working with the same GFAJ-1 bacteria as in the original experiment. Her next step is to add arsenic to the growth medium and see if that improves growth.
Replicating -- or not -- results such as these is important practice, especially when the rigor of the original experiments is so widely questioned. This is out of our technical area, but seems to show the positive side of scientific confirmation, a core part of scientific epistemology, at its best.
Unfortunately, this kind of replication is often impossible in genetics or evolution, because we can't replicate others' samples or see evolution at work over millions of past years. Even new samples, on evolutionary grounds, cannot be assumed to be 'replicates' of other samples, because of the amount of genetic variation, environmental effects, and so on, that is inevitably involved. So the fact that the arsenic experiment can be redone so elegantly is a thing of beauty -- and envy, to geneticists.
Of course, even if Redfield demonstrates to most people's satisfaction that her bacteria do not incorporate arsenic into their DNA, that doesn't show that it couldn't happen. Nor that it hasn't happened (see our original post on this issue with respect to what it might mean if it had, as reported in 1980). Nor even, in principle at least, that it couldn't happen. Those are biochemical issues. The important issue in the context of the original spacey claims is that evolution works with what is at hand. Whether something can occur under earthly conditions, using bacteria that have 4 billion years of ancestry on this Earth and its environments, has absolutely no bearing on whether it might have occurred on some other planet.
More to the point, it has no bearing whatever on whether 'life' much less 'intelligent life' exists on other planets. NASA is pulling the wool over your eyes if you don't see that. We've posted on the life-in-space issue a couple of months ago.
So let's keep the issues separated. Can earth-like life, after 4 billion years, survive without phosphorous? Was the arsenic-life report reliable? Is there life elsewhere, and if so, what might it be like?