Intracellular competition shapes plasmid population dynamics.

Area of Science:

• Evolutionary biology
• Microbial genetics
• Molecular evolution

Background:

• Multilevel selection drives evolution across biological scales, from organisms to intracellular elements like plasmids.
• Plasmids, self-replicating genetic elements in bacteria, are key to their evolutionary adaptability but face intra-cellular competition.
• Understanding within-cell plasmid fitness dynamics is crucial for evolutionary theory but experimentally challenging.

Purpose of the Study:

• To experimentally measure within-cell fitness of competing plasmids.
• To characterize the drift and selective dynamics governing plasmid evolution.
• To investigate the impact of gene expression and trait dominance on plasmid fixation.

Main Methods:

• Controlled splitting of synthetic plasmid dimers to establish balanced competition.
• Measurement of within-cell plasmid fitness and selective advantages.
• Analysis of plasmid co-occurrence dynamics, including methylation-based eclipsing.

Main Results:

• Incompatible plasmids co-occur longer than expected due to methylation-based eclipsing.
• Less transcriptionally active plasmids exhibit a within-cell selective advantage, favoring silent plasmids.
• A trade-off exists between cell-plasmid fitness and trait dominance, affecting invasion and fixation probabilities.

Conclusions:

• Plasmid evolution is shaped by joint dynamics at both within-cell and population levels.
• Transient within-cell selection plays a critical role in plasmid evolutionary trajectories.
• Plasmid-encoded trait dominance influences evolutionary outcomes, with more dominant traits being less likely to fix.