Bacteria that produce manganese (Mn) oxides are extraordinarily skilled engineers of nanomaterials that contribute significantly to global biogeochemical cycles. However, mineralization mediated by these organisms is poorly understood because enzymes involved in these processes are largely uncharacterized. A recent study revealed for the first time the structure of Mnx—a bacterial enzyme complex responsible for Mn biomineralization—and the Mn oxide nanoparticles it produces.