What makes understanding the ecology and evolution of microbes such a unique challenge is the fact that, while the life of microbes unfold at scales of a few micrometers, their impact on ecosystems can be perceived at the scale of meters or kilometers. Our inability to map ecosystem-level processes to the micro-scale interactions that take place in microbial communities is one of the main obstacles hindering the development of mechanistic models that allow us to interpret microbial diversity and predict community dynamics. The overarching goal of this research project is to understand how the biotic interactions between microbes at the scale of micrometers impact microbial community structure and dynamics. By reconstructing the spatial structure and the interaction networks of microbial populations colonizing particles of a few tens of microns in diameter in aquatic environments, the proposed research will build mechanistic models that will serve to i) clarify the structure-function mapping of microbial ‘species’ in the environment, ii) understand microbial community assembly at the relevant physical scales iii) model how perturbations in the environment lead to micro-scale shifts in community structure and iv) elucidate how biotic interactions influence genome evolution in microbial communities. The results of this project will fill a fundamental gap in microbial sciences, allowing us to connect micro-scale population and community interactions to the global diversity and function of microbial communities.