It's not as spectacularly different as I first thought, apparently it only incorporates arsenic into its DNA when phosphorous is hard to come by.
Guardian science.
That is a pretty big 'only'.
It is a momentous paper (I've just read it). However, the data presented is just one strand of the puzzle. They provide evidence that if you purify the genomic DNA from the bacterium you get a) an anomalously high As:C ratio and low P:C ratio to what you would expect and b) X-ray edge diffraction techniques indicate that the As is in valence state (V) and probably bound as C-O -As(=0)2-O-C which would be a direct equivalent of the phosphorous in DNA.
So it looks very much like it but the evidence is not conclusive - strongly suggestive, yes, but not conclusive.
What is interesting is the chemistry. As is a direct analogue of P but is far more reactive, hence molecules are less stable. Also, the way they are assembled may be dependent on quantum effects in the enzyme mechanisms, which will be affected by the change in electron shell structure between As and P.
I can imagine that very soon we will have the complete DNA sequence of the organism and be able to start reconstructing the machinery
in vitro to assess this chemical conjuring capability.
In other words 'Fairly normal bug but it has learned how to tolerate Arsenic'. I think we will find many more, especially with trace elements if we look hard enough in the right places.
Should keep the coffee room conversation going tomorrow though.
