PROJECT SUMMARY The gastrointestinal tract is home to trillions of microorganisms that play an essential role in early life development and the maintenance of health. Shortly after birth, newborns are rapidly colonized by this complex microbial community that possesses a rich metabolic potential. Perturbation to assembly of the microbiota can have major downstream consequences to health. However, the fundamental ecological principles and molecular processes that underlie establishment of a beneficial and stable microbial community are largely unknown. Defining the multidimensional interactions in this complex ecosystem has proven incredibly challenging and has not moved far beyond simple associations. This is in part due to the inherent complexity and interconnectedness of the microbiota and a lack of fundamental mechanistic studies at this interface. Moreover, there are limited technologies available to spatially map and study metabolic cross talk between species in the microbiota. Here, we propose a novel strategy to generate a molecular blueprint of the metabolic interactions in the assembling microbiota using an innovative pipeline that integrates advanced imaging metabolomics with comprehensive mechanistic studies. Our objective is to generate a high-resolution spatial map of metabolites during community assembly and perturbation. We will use this molecular map to systematically determine the mechanisms of metabolic cross talk between members of the microbiota and define the role of these interactions in assembly of communities. We will study colonization and deconstruct mechanisms of community assembly using simple synesthetic microbial communities, gnotobiotics, and continuous flow cultivar systems. Our goal is to provide a detailed understanding of the spatial localization and molecular mechanisms of metabolic interactions in the microbiota during early life. Furthermore, we will define the molecular determinants that confer increased fitness for early life colonizing organisms. Together, this proposal will provide a framework for understanding the fundamental mechanisms of community assembly in infants and lead to the development of novel strategies for manipulating microbial communities in early life and during microbiota-associated disease.