Garcillan-Barcia, M. d. P. | bioRxiv Science

bioRxiv2023

Fundamental parameters governing the transmission of conjugative plasmids

Because their ability to spread infectiously, conjugative plasmids represent a major route for the propagation of antibiotic resistances. In the wild, there are hundreds of different plasmids, but their distribution, prevalence and host range are extremely variable. To understand the reasons behind these ecological differences, we need to obtain precise models for plasmid transmission dynamics. Here, we show that the dynamics of plasmid transmission follow a simple ecological model known as Hollings Type II Functional Response. Plasmid transmission dynamics can be faithfully captured using two parameters: the searching rate (the pace at which a donor bacterium encounters a suitable recipient) and the handling time (the time required for a donor to transfer the plasmid). By analyzing the dynamics of different plasmid prototypes, we show that these parameters are characteristic of the plasmid transfer machinery. Quantifying the dynamics of plasmid spread may shed light on the epidemiology of antibiotic resistance genes.

microbiology↗

bioRxiv2021

Evolution of plasmid mobility: origin and fate of non-conjugative plasmids

Conjugation drives horizontal gene transfer of many adaptive traits across prokaryotes. Yet, only a fourth of the plasmids encode the functions necessary to conjugate autonomously, others being non-mobile or mobilizable by other elements. How these different plasmids evolve is poorly understood. Here, we studied plasmid evolution in terms of their gene repertoires and relaxases. We observed that gene content in plasmid varies rapidly in relation to the rate of evolution of relaxases, such that plasmids with 95% identical relaxases have on average fewer than 50% of homologs. The identification of 249 recent transitions in terms of mobility types revealed that they are associated with even greater changes in gene repertoires, possibly mediated by transposable elements that are more abundant in such plasmids. These changes include pseudogenization of the conjugation locus, exchange of replication initiators, and extensive gene loss. In some instances, the transition between mobility types also leads to the genesis of novel plasmid taxonomic units. Most of these transitions are short-lived, suggesting a source-sink dynamic, where conjugative plasmids constantly generate mobilizable and putatively non-mobilizable plasmids by gene deletion. Yet, in few cases such transitions resulted in the emergence of large clades of relaxases present only in mobilizable plasmids, suggesting successful specialization of these families in the hijacking of diverse conjugative systems. Our results shed further light on the huge plasticity of plasmids, suggest that many non-conjugative plasmids emerged recently from conjugative elements and allowed to quantify how changes in plasmid mobility shape the variation of their gene repertoires.

evolutionary biology↗