Main goal. We aim to understand the puzzling coexistence of antibiotic-resistant and antibiotic-sensitive species in natural soil environments, using novel quantitative experimental techniques and mathematical analysis. The ecological insights gained will be translated into novel treatment strategies for combating antibiotic resistance.Background. Microbial soil ecosystems comprise communities of species interacting through copious secretion of antibiotics and other chemicals. Defence mechanisms, i.e. resistance to antibiotics, are ubiquitous in these wild communities. However, in sharp contrast to clinical settings, resistance does not take over the population. Our hypothesis is that the ecological setting provides natural mechanisms that keep antibiotic resistance in check. We are motivated by our recent finding that specific antibiotic combinations can generate selection against resistance and that soil microbial strains produce compounds that directly target antibiotic resistant mechanisms.Approaches. We will: (1) Isolate natural bacterial species from individual grains of soil, characterize their ability to produce and resist antibiotics and identify the spatial scale for correlations between resistance and production. (2) Systematically measure interactions between species and identify interaction patterns enriched in co-existing communities derived from the same grain of soil. (3) Introducing fluorescently-labelled resistant and sensitive strains into natural soil, we will measure the fitness cost and benefit of antibiotic resistance in situ and identify natural compounds that select against resistance. (4) Test whether such “selection-inverting” compounds can slow evolution of resistance to antibiotics in continuous culture experiments.Conclusions. These findings will provide insights into the ecological processes that keep antibiotic resistance in check, and will suggest novel antimicrobial treatment strategies.