The human intestinal microbiota is a complex and dynamic consortium of microbes that is crucial for human health and disease prevention. Our lab has been studying the abundant bacterial members of this ecosystem to understand how they interact with each other both cooperatively and antagonistically to form these health-promoting communities. We use basic microbiological, genetic, biochemical, and gnotobiotic mouse analyses, combined with genomic, metagenomic and computational analyses to understand these complex interactions. We have discovered numerous classes of new antimicrobial proteins that these bacteria use to compete in their ecosystem, and we are studying their mechanisms of action, ecological properties, and how we may translate these molecules for human health benefits. Another focus of the lab is the evolution of microbes in the human gut and how genetic elements horizontally transferred between bacterial species personalize each individual’s gut microbiota and the phenotypes and community benefits conferred by these shared genetic elements.