Anupama Khare "Systems-level investigation of multi-species bacterial interactions" Abstract: Microorganisms typically exist in multispecies communities, where species present in close proximity interact with each other. Such interactions affect the fitness and survival of the interacting species, but the mechanisms underlying such interactions, and potential adaptive pathways, remain largely uncharacterized. Most previous studies of multispecies systems have focused on the effect of a specific molecule or pathway of interest on exogenous species. Here, I utilized an unbiased genome-scale approach to identify and characterize multifaceted competition in a model two-species system containing Pseudomonas aeruginosa and Escherichia coli. I discovered both forms of ecological competition in the antagonism of E. coli by P. aeruginosa – sequestration of iron led to exploitative competition, while phenazine exposure engendered interference competition. I also identified adaptive evolutionary trajectories of E. coli that increase resistance to P. aeruginosa toxins using laboratory evolution studies, observing parallel molecular evolution and adaptive convergence at the gene-level. My study thus reveals the molecular complexity of a simple two-species interaction, and is an important first-step in the application of systems biology to detailed molecular dissection of interactions within native multispecies systems.