This paper presents a research article that investigates the conflicts between different levels of biological organization-specifically, how plasmids (extrachromosomal, self-replicating genetic elements) experience competition both within their host cell (within-cell) and between different host cells (between-cell). The authors use a novel experimental system involving synthetic plasmid dimers, which can be split to initiate balanced within-cell competition, and microfluidic devices (mother machines) to isolate and measure these intracellular dynamics. Key findings show that plasmid transcriptional activity imposes a within-cell fitness cost, favoring gene loss, while regulatory mechanisms like hemimethylation can prolong the coexistence of competing plasmids, and the translational strength of genes on the plasmid modulates the interplay between within- and between-cell selection, impacting how efficiently beneficial traits (like antibiotic resistance) fix in the bacterial population. These results highlight the complex, non-trivial evolutionary dynamics that govern the spread of plasmids, including those carrying antibiotic resistance genes.

References:

• Rossine F, Sanchez C, Eaton D, et al. Intracellular competition shapes plasmid population dynamics[J]. bioRxiv, 2025.