Antibiotics Interfere with the Evolution of Plasmid Stability.

Area of Science:

• Bacterial genetics
• Evolutionary biology
• Molecular microbiology

Background:

• Extra-chromosomal genetic elements, such as plasmids, significantly influence bacterial evolution.
• Plasmid-encoded genes, like antibiotic resistance, are maintained under positive selection.
• Plasmid carriage can impose a metabolic burden, potentially leading to plasmid loss without selection.

Purpose of the Study:

• To investigate how positive selection impacts the evolution of plasmid stability.
• To understand the transition of plasmids into stably inherited genetic elements.
• To determine if plasmid-mediated advantages affect long-term plasmid evolutionary success.

Main Methods:

• Evolving plasmids in Escherichia coli under varying selection pressures (antibiotics vs. no antibiotics).
• Analyzing plasmid amplification and stability.
• Surveying naturally occurring Escherichia plasmids.

Main Results:

• Positive selection for plasmid-encoded genes, specifically antibiotic resistance, led to plasmid amplification and instability.
• Suboptimal plasmid stability solutions were maintained under positive selection, hindering long-term persistence.
• Antibiotic resistance genes are infrequently found on small plasmids in Escherichia.

Conclusions:

• Positive selection for plasmid-borne traits can interfere with the evolution of plasmid stability.
• Plasmid-mediated benefits may paradoxically reduce a plasmid's evolutionary success.
• Understanding plasmids as autonomous evolving entities is crucial for their evolutionary studies.