Plasmid-free cheater cells commonly evolve during laboratory growth

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Antibiotics are crucial for clinical use and laboratory plasmid selection.
• Antibiotic resistance mechanisms can act as public goods, benefiting neighboring cells.
• The impact of these cooperative mechanisms on plasmid stability in lab settings is unclear.

Approach:

• Investigated plasmid curing in surface-grown bacteria using beta-lactamase, aminoglycoside phosphotransferase, and tetracycline antiporter resistance.
• Compared plasmid maintenance in liquid versus surface growth conditions under antibiotic selection.
• Assessed the generation of heterogeneous cell populations due to plasmid loss.

Key Points:

• Plasmid-encoded beta-lactamases significantly increase plasmid curing in surface-grown bacteria.
• Aminoglycoside phosphotransferase and tetracycline antiporter mechanisms also contribute to plasmid loss.
• Liquid growth offers more robust plasmid maintenance than surface growth, but plasmid loss still occurs.

Conclusions:

• Antibiotic resistance mechanisms can lead to unintended plasmid loss in laboratory settings.
• This plasmid loss generates mixed populations of resistant and susceptible cells, complicating experimental results.
• Researchers must consider plasmid stability when using antibiotic selection for plasmid maintenance.