Positive selection and compensatory adaptation interact to stabilize non-transmissible plasmids.

Area of Science:

• Bacterial genetics
• Evolutionary biology
• Microbial genomics

Background:

• Plasmids drive bacterial evolution but their long-term persistence is poorly understood due to carriage costs.
• Classical models emphasize horizontal transfer for plasmid maintenance, yet many plasmids are non-transmissible.
• Understanding non-transmissible plasmid persistence is crucial for bacterial evolution and antibiotic resistance studies.

Purpose of the Study:

• To investigate the maintenance mechanisms of a costly, non-transmissible plasmid (pNUK73) in Pseudomonas aeruginosa.
• To determine the roles of compensatory adaptation and selection in plasmid stability.
• To elucidate how these factors interact to ensure plasmid persistence.

Main Methods:

• Mathematical modeling of plasmid dynamics.
• Experimental evolution of Pseudomonas aeruginosa populations carrying pNUK73.
• Analysis of plasmid stability and bacterial adaptation.

Main Results:

• Compensatory adaptation significantly reduces the cost of plasmid carriage, enhancing plasmid stability.
• Positive selection for plasmid-encoded antibiotic resistance is essential to counteract segregational loss.
• Compensatory adaptation and positive selection act synergistically to maintain non-transmissible plasmids.

Conclusions:

• Non-transmissible plasmids can persist through a combination of bacterial adaptation and selection.
• This study offers novel insights into plasmid maintenance strategies in bacterial populations.
• The findings explain the long-term persistence of antibiotic resistance even after antibiotic withdrawal.