The OMM12 model after ten years: what did we learn about the gut microbiome from a defined microbial community?

Over the past decade, the Oligo-Mouse-Microbiota (OMM 12 ) has emerged as a cornerstone model for mechanistic studies of the gut microbiome. As a rationally designed, defined microbial community, OMM 12 reduces the complexity of the native microbiota while preserving key ecological and functional traits of the murine gut ecosystem. Comprising twelve culturable, genome-sequenced, and phenotypically characterized strains of murine origin, the model enables reproducible and stable colonization across hosts and experimental settings. Initially developed to study colonization resistance, OMM 12 has since been widely applied across diverse fields, including microbial ecology, immunology, and computational biology, providing fundamental insights into host–microbe and microbe–microbe interactions. Its broad adoption has been supported by the development of a rich experimental and computational toolbox, including strain-resolved sequencing, metabolomics, and metabolic modeling approaches. Here, we review a decade of OMM 12 research, highlighting its design principles, methodological advances, and key scientific discoveries, and we additionally provide an overview of available resources, including a newly established website (daisybio.ls.tum.de/omm12/) that consolidates tools, protocols, and datasets to facilitate community use. Together, this review underscores the continued importance of OMM 12 as a versatile platform for causal and quantitative microbiome research.