The Evolution of Plasmid Transfer Rate in Bacteria and Its Effect on Plasmid Persistence

Abstract

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A mathematician’s guide to plasmids: an introduction to plasmid biology for modellers

“…It seems that conjugation rates can be higher in vivo than in vitro [272][273][274]. Like most -if not all -traits, the conjugation rate is itself subject to evolution [275,276]. As the conjugation rate can be controlled by the host, the recipient cell, or the plasmid, evolution of both bacteria and plasmids can change how much transfer occurs.…”

Evolution of horizontal transmission in antimicrobial resistance plasmids

“…Other plasmids present in the donor cell can also modify a focal plasmid's transfer rate by various mechanisms [99,100]. Because the donor cell pays the cost of higher transmission, direct selection acts on genes present in donors (on the chromosome as well as on any other MGE that is not transmitted together with the focal plasmid) to decrease transmission rates [24]. Yet, plasmid transmission to recipient cells then affects the fitness of these new hosts, which indirectly affects donor fitness: if donors are related to recipients, transferring beneficial plasmids -for instance AMR plasmids in the context of antibiotic treatment -increases the inclusive fitness of donor alleles [101].…”

“…One key characteristic of the life cycle of MGEs is that they can transmit within populations via two routes: vertical transmission together with host cell division, and horizontal transmission from a donor to a recipient bacterium. If horizontal transmission conferred no costs, it would evolve towards always increasing rates [24]. However, an MGE with high rates of horizontal transmission will impose a higher cost to its bacterial host, leading to reduced host growth or competitive ability.…”

“…Over evolutionary times, MGEs might thus evolve towards some optimal transmission rate that depends on the costs of transmission and the opportunities for transfer they experience. However, models have shown that evolution does not necessarily converge to a single transfer rate, but low-frequency genetic diversity in transfer rates can be stable [24]. Moreover, when host availability varies over time, plasticity mechanisms that induce transmission only when a high density of potential hosts is detected can benefit both phages [36] and plasmids [37].…”

“…Regardless, this variation will influence MGE spread and distribution in bacterial populations. A recent model showed that effects of several orders of magnitude are required for host cells to significantly alter plasmid prevalence [24]. Thus, small effects might have little consequences, but large variations in transfer ability will impact AMR plasmid prevalence.…”