In microbial populations, conjugative plasmids are pivotal in fostering genetic diversity and evolution. These extrachromosomal DNA entities, prevalent in bacteria and related microorganisms, are known to confer antibiotic resistance. However, their acquisition can entail immediate and long-term fitness costs for their hosts. While the persistent fitness costs are well-documented, our understanding of the transient, immediate costs incurred upon plasmid acquisition remains limited. This research endeavor led by Allison Lopatkin, Assistant Professor of Chemical Engineering at the University of Rochester, focuses on unveiling the physiological consequences and population-level implications of plasmid acquisition.

To address this knowledge gap, the study scrutinized the growth dynamics of individual bacterial colonies immediately following plasmid acquisition, encompassing a diverse array of conditions, plasmid types, selection environments, and clinical strains. Intriguingly, the findings defy conventional wisdom, revealing that plasmid acquisition costs are predominantly driven by changes in lag time rather than growth rate. Remarkably, for costly plasmids, colonies displaying extended lag times exhibit accelerated recovery growth rates, suggesting an unexpected evolutionary tradeoff. This phenomenon has profound ecological repercussions, wherein intermediate-cost plasmids outcompete their low and high-cost counterparts, showcasing the complexity of plasmid cost dynamics.

This study uncovers a counterintuitive aspect of plasmid-mediated gene transfer, shedding light on the intricate interplay between lag time and growth rate. Such insights deepen our comprehension of plasmid acquisition and have implications for predicting the ecological outcomes and devising intervention strategies in bacterial populations undergoing conjugation. By unraveling the underlying factors governing plasmid costs, this research contributes to combating antibiotic resistance and harnessing plasmids as tools for various applications, from environmental remediation to microbial community engineering. Furthermore, ongoing investigations into the genetic and environmental determinants of horizontal gene transfer aim to enhance our ability to foresee high-risk gene transfer events and develop innovative control and treatment strategies.

The study’s findings were published in Nature Communications.

References

• Ahmad, M., Prensky, H., Balestrieri, J., ElNaggar, S., Gomez-Simmonds, A., Uhlemann, A.-C., Traxler, B., Singh, A., & Lopatkin, A. J. (2023). Tradeoff between lag time and growth rate drives the plasmid acquisition cost. Nature Communications, 14(1), 2343. https://doi.org/10.1038/s41467-023-38022-6
• University of Rochester. (2023, September 14). Scientists uncover surprising twist in the ways bacteria spread antibiotic-resistant genes. Phys.Org. https://phys.org/news/2023-09-scientists-uncover-ways-bacteria-antibiotic-resistant.html