The effects of ecological interactions and distinct conjugation rates on the invasion of a conjugative plasmid in bacterial communities

• Weaker competition or stronger mutualism in a community decreases plasmid invasion • The origin of the plasmid-bearing population determines plasmid invasion and spread • Model confirms role of interspecies conjugation rate differences in plasmid spread Mathematical models that are used to study the persistence and spread of antibiotic resistance plasmids usually describe conjugation within a single bacterial species or neglect ecological interactions and differences in conjugation rates between species. To increase our understanding of the role of differences between species in plasmid dynamics in a bacterial community, we extend the generalised Lotka-Volterra model with plasmid-bearing populations and density-dependent conjugation. With this model, we investigate how ecological interactions between species with distinct conjugation rates affect the invasion and spread of a conjugative plasmid in a bacterial community. We find that the possibility for plasmid invasion mediated by a species that was already present in the modelled plasmid-free communities is mainly determined by the intraspecies conjugation rate of the initially plasmid-bearing species and the fitness costs of bearing a plasmid. In contrast, the possibility for plasmid invasion mediated by a species that was not yet present in the plasmid-free community is mainly determined by ecological interspecies interactions involving the initially plasmid-bearing species. Nevertheless, decreased interspecies conjugation rates to and from the initially plasmid-bearing species reduce the spread of a plasmid through the community. In both scenarios, weaker competitive and stronger mutualistic ecological interspecies interactions reduce the spread of a plasmid through the community, limiting the creation of new plasmid-host combinations. Our results indicate that ecological interactions and differences in conjugation rates between species should be taken into account when modelling the invasion and spread of plasmids.