IncQ Satellite Plasmid Evolution

We performed experimental evolution on bacteria carrying an IncQ plasmid to understand how this type of broad-host-range plasmid is stably maintained after it is transferred to a new host cell. We found that small satellite plasmids rapidly evolved that had lost the ability to autonomously replicate and deleted a burdensome plasmid cargo gene. Coexistence of these satellite plasmids with the full-length plasmid reduced the cost of maintaining some functional copies of the new accessory gene for longer before they were lost. This mechanism that stabilizes the maintenance of newly acquired genes carried by an IncQ plasmid may contribute to their important role in the spread antibiotic resistance genes.