
Many microbes are co-residents in our bodies, providing beneficial services in exchange for some of our resources. It’s a relationship called mutualism in which we provide a comfortable home, and they return the favor in myriad, interesting ways. Science is just beginning to scratch the surface of what the microbes in our bodies do for us. Until now, scientists have only had a murky understanding of how these relationships arise. Now Colin Dale and his colleagues at the University of Utah have an answer. It’s good news and bad news, germophobes: The bad news? Mutualistic bacteria start out by invading animal cells just like malevolent disease-causing bacteria do. The good news? Once they’re in, they calm down and play nice.



















