Essential gene acquisition destabilizes plasmid inheritance

Extra-chromosomal genetic elements are important drivers of evolutionary transformations and ecological adaptations in prokaryotes with their evolutionary success often depending on their utility to the host. Examples are plasmids encoding antibiotic resistance genes, which are known to proliferate in the presence of antibiotics. Plasmids carrying an essential host function are recognized as permanent residents in their host. Essential plasmids have been reported in several taxa where they often encode essential metabolic functions. Essential genes are rarely encoded on plasmids; evolving essential plasmids in Escherichia coli we find that essential gene acquisition can lead to plasmid extinction. Our results suggest that essential plasmid emergence leads to a dose effect caused by gene redundancy. The detrimental effect of essential gene acquisition on plasmid inheritance constitutes a barrier for plasmid-mediated lateral gene transfer and supplies a mechanistic understanding for the rarity of essential genes in extra-chromosomal genetic elements.