A year and a half ago, NASA announced that one of its scientists, Felisa Wolfe-Simon, had found a bacterium that could use arsenic instead of phosphorus in its DNA. This revelation, published in Science, had enormous implications for our understanding of what's necessary for life---we've always thought phosphorus was essential and arsenic poisonous, and having that disproven might mean life could exist in environments where it had been thought impossible. Almost immediately, though, scientists and science journalists began to pick apart this paper. DISCOVER blogger Carl Zimmer rounded up the case against in a Slate article shortly after the paper's publication. Ever since, he's kept track of the story's evolution---including experiments posted by microbiologist Rosie Redfield on her blog that provided evidence against the claim---here on his blog. All the way along, Wolfe-Simons refused to comment on Redfield's experiments, saying she would wait until they were published by a peer-reviewed journal. Now, Redfield's paper and one other paper finding no evidence of arsenic life have been published by Science, the same journal that published the original claim. The researchers found no evidence of arsenic being used in the bacterium's DNA. The authors note that it can survive at very low concentrations of phosphorus and can handle concentrations of arsenic an order of magnitude higher than other cells, which is neat, but not evidence that it can actually use arsenic--chemical tests showed that there was no arsenic in the bacterium's DNA. Wolfe-Simons, now open to talking about the work, said something very peculiar in corresponding with Alan Boyle of MSN: "There is nothing in the data of these new papers that contradicts our published data." It's hard to see how she can think that; however, she and her collaborators appear to be alone in that conviction. For more, check out Carl's live-blog of Redfield's talk about the work at a recent conference.