In December of last year, NASA Astrobiology Program Postdoctoral Fellow Felisa Wolfe-Simon and collaborators published a paper online in Science Express describing a bacterium that substitutes arsenic for phosphorus to sustain its growth when in arsenic-rich, phosphorus-depleted medium. Their data showed evidence for arsenate in macromolecules that normally contain phosphate, most notably nucleic acids and proteins. In response to considerable feedback, Science Express has published eight technical comments and a response from Wolfe-Simon and her collaborators. The final version of the original paper will appear in the June 3 print issue of Science. Wolfe-Simon’s research is supported by NASA’s Exo/Evo Program and the NAI.