Link is to one of two (here’s the other) articles just published refuting the original study claiming that a newly isolated organism was replacing phosphodiester bonds with arsenodiesters in the backbone of DNA. The result isn’t much of a surprise to begin with when you consider that (a) Getting rid of all phosphorous in growth media is practically impossible, so there will likely always be trace amounts. (b) Simple chemistry suggested that this should never happen. Phosphodiester bonds are in DNA because they are stable; arsenodiester bonds, on the other hand, are not. This would have required ways of stabilizing these bonds, which would have required a large expenditure of energy from the cells; something they could not afford in the nutrient-depleted environments from which they were isolated and in which they were grown. (c) The authors of the original paper did a good job of proving that the organism was resistant to Arsenate and that it could survive with little Phosphate, but the actual claim didn’t match the data. There were several experiments that were clearly left off which would be able to prove their case beyond a shadow of a doubt, but they didn’t do them. This is what would be expected if work were rushed to press before it’s ready because of potential headlines or if experiments didn’t give the appropriate results and were ignored (I don’t remember seeing any evidence of the latter, so I would assume the former rather than accuse anyone of impropriety).
Today’s articles basically present data to prove what a large number of people assumed was the case right from the beginning: There wasn’t arsenic-based life isolated. There is, however, an organism which can survive with reasonably high levels of arsenate present which can also manage to scrounge quite low levels of phosphate to survive. It’s impressive, but it’s not something that would usually make people call news conferences.