Self-organisation and persistence of antibiotic resistance in evolving plasmid communities

ABSTRACT A key source of genetic variation of microbial populations are plasmids: extrachromosomal genetic elements that replicate autonomously and can be highly mobile between individual cells. Diverse plasmids were found in environmental samples and bacterial populations. Here we explore the mechanisms that help to preserve this gene pool as a fundamental basis for bacterial adaptation. An individual-based model of the plasmidome is presented and used to investigate how intra- and intercellular competition between diverse plasmid types affects the evolution of plasmid communities. It indicates the relative importance of stochastic and deterministic drivers of plasmid persistence both under neutral conditions and when the environment selects for specific plasmid-encoded traits such as antibiotic resistance for a certain period of time. We found that evolving plasmid communities exhibit a cyclical dynamics that contributes to the maintenance of plasmid diversity and the persistence of costly plasmid-mediated antibiotic resistance after stopped abiotic selection.