Abstract
Many plants and animals, including humans, host diverse communities of microbes that provide many benefits. A key challenge in understanding microbiomes is that the species composition often differs among individuals, which can thwart generalization. Here, we argue that the key to identifying general principles for microbiome science lies in microbial metabolism. In the human microbiome and in other systems, every microbial species must find ways to harvest nutrients to thrive. The available nutrients in a microbiome interact with microbial metabolism to define which species have the potential to persist in a host. The resulting nutrient competition shapes other mechanisms, including bacterial warfare and cross-feeding, to define microbiome composition and properties. We discuss impacts on ecological stability, colonization resistance, nutrient provision for the host, and evolution. A focus on the metabolic ecology of microbiomes offers a powerful way to understand and engineer microbiomes in health, agriculture, and the environment.