S eeing “nitrification” and “Archaea” in the title of the paper in PNAS by Alonso-Sáez et al. (1) will not surprise anyone following the story about the role of these microbes in an important pathway of the nitrogen cycle. What will puzzle, if not surprise, everyone is the other key word, “urea.” That nitrogenous compound never comes up in discussions of nitrification and Archaea, and even othe...
