Abstract
Microorganisms commonly live in diverse communities where changes in composition can be critical for health, industry and the environment. Yet, what enables one strain to competitively replace another in these complex conditions remains poorly understood. Here we develop a mathematical model to determine general principles of strain displacement. Our modelling reveals that weak resource competition enables successful invasion while strong interference competition, for example, via antimicrobial production, enables successful displacement. We verify these predictions using in vitro assays with genetically engineered Escherichia coli. We then apply our principles to displace multidrug-resistant clinical isolates using strains that are equipped with a potent bacteriocin. Finally, we perform experiments with diverse human gut symbionts, which reveal that displacement relies on low resource competition not only between competing strains but also with the broader community, that is, limited nutrient blocking. These general rules for ecological success in microbial communities could be applied for targeted displacement of bacteria.