In this interview, Prof. James Versalovic says that, as for the Human Genome Project, we’re only witnessing the first steps of gut microbiota research. In the course of the past few years, the scientific question has evolved from “what bacteria live with us?” to “what do they do?”, a key element when trying to define the gut microbiota as a multi-cellular microbial organ, which together with the other human organs make up the human body.