Arsenic-loving bacteria probably a mistake

Remember a few years back when NASA announced the discovery of a new form of life, a bacteria that was able to incorporate arsenic into its cell components, instead of phosphorus, as is somewhat more Earth-life like? This was a very significant and exciting discovery because it allowed for a broader spectrum of possible life forms that might evolve in outer space, which, for a lot of scientists (and sci-fi loving nerds), is a HOLY SHIT YES kind of possibility. I mean, think about it - arsenic is a poison, and this microbe thrives and reproduces using this toxin, instead of a basic chemical constituent like phosphorus. Massively cool, right?
GFAJ-1, an exciting new life-form.
Well, turns out NASA was probably wrong. In two new papers published in the journal Science the authors (Reaves et al. and Erb et al.) show that the bacteria can’t use arsenic for growth, but, in fact, depends on phosphorus. It is, however, very resistant to arsenic (more than other arsenate resistant strains) and "is able to grow in the presence of very high arsenate and limiting phosphate concentrations" (Erb et al.). Furthermore, its core metabolism is "based on phosphorylated metabolites, even when cells are grown at high concentrations of arsenate and low concentrations of phosphate" (Erb et al.). For more details refer to the original articles. You will have to register to read them in full, but the registration is free and the benefits great (like getting the access to all of Science's publications back to 1997), so there's really no reason not to do it.

So, that's a bit disappointing, isn't it? Well, yes and no. It is disappointing because it means no arsenic munching aliens probably exist. What is great about this story, however, is that, even though this was supposed to be a huge and revolutionary discovery, scientists tried to falsify it and apparently managed to do so (read more about the importance of trying to falsify scientific theories here). This is a great example of how science works - no matter how exciting the theory might be, and how important its conclusions, it is still expected to sustain lots and lots of nit-picking and then some more experimenting before earning the right to be considered valid. It shows how, in science, there is no such thing as 'dogma', and every discovery can be re-tested at any point in time and, if shown wrong, discarded as such. It doesn't mean that science is wrong, it means it always corrects itself, learns on its mistakes and grows to be more reliant and to make less mistakes. When these happen again, however, scientists will again reveal them, give a detailed description of them, and then correct them. That's the strength of the scientific method - even mistakes are accepted as necessary, and not as something to be ashamed or afraid of.

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