Every living thing on the planet has to contend with bacteria. To many viruses, they are prey. To other bacteria, they are competitors. To animals and plants, they can be the cause of devastating diseases or beneficial partners that provide everything from nutrition to immunity to light. They have been around for some 3 billion years, and they are everywhere. So, it makes sense that a gene which allows its owners to deal with bacteria might find a home throughout the entire tree of life.

That’s what Jason Metcalf and colleagues from Vanderbilt University have now discovered. They tracked a gene called GH25-muramidase, which makes an enzyme that can break apart a bacterium’s outer wall. It’s common in bacteria, which