Segregational Drift and the Interplay between Plasmid Copy Number and Evolvability

Area of Science:

• Microbiology
• Evolutionary Biology
• Genetics

Background:

• Plasmids are ubiquitous in prokaryotes and can transfer between cells.
• Multicopy plasmids lead to increased mutation supply but face challenges in allele segregation.
• Segregational drift, the random drift of plasmid copies during cell division, impacts plasmid evolution.

Purpose of the Study:

• To investigate the evolutionary implications of segregational drift in multicopy plasmids.
• To determine how plasmid copy number affects evolutionary rate and mutation dynamics.
• To analyze the impact of plasmid evolution on host chromosome evolution.

Main Methods:

• Experimental evolution of low- and high-copy plasmids in Escherichia coli.
• Simulations of multicopy plasmid allele evolution.
• Examination of experimentally evolved host chromosomes.

Main Results:

• The evolutionary rate of multicopy plasmids did not correlate with their copy number.
• Segregational drift increased mutation loss frequency and fixation time compared to chromosomes.
• Plasmid type significantly impacted host chromosome evolution.

Conclusions:

• Segregational drift hinders the retention and fixation of novel plasmid variants.
• Plasmid genomes can evolve slower than haploid chromosomes despite higher mutation rates.
• Plasmid copy number is a key factor in plasmid evolability due to segregational drift.