We propose to employ EMSL's state-of-the-art metabolomics capabilities to gain a predictive understanding of how compartmentalized metabolic reactions are coordinated across carbon and energy exchanges in microbial communities. We seek to quantitatively determine and predict the flux of metabolites through microbes connected by carbon exchange. To accomplish this, we will constrain our investigation to model microbial consortia composed of cross-feeding heterotrophic bacteria that can be cultivated on defined media, have sequence/annotated genomes and pre-constructed genome-scale metabolic network models. This study will employ an integrative theoretical and experimentation approaches to capitalize upon our team's expertise in advanced microbial co-cultivation, metabolic modelling in combination with EMSL's emerging expertise in 13C Metabolic Flux Analysis. This proposed collaboration with EMSL will enable a broader team scientists, working under a Scientific Focus Area (PNNL's FSFA) sponsored by DOE Office of Science, to learn fundamental biological principles of microbial interaction that control carbon transformation at the community scale. With EMSL's help, we expect the success of this project to be highly impactful as it aims to make a considerable advancement over the current state of this science by integrating 13C-labled metabolic flux analysis and community scale metabolic simulations to quantify and predict the flux of carbon through interacting species in a microbial community.