Increased copy number couples the evolution of plasmid horizontal transmission and plasmid-encoded antibiotic resistance

Abstract

Conjugative plasmids are mobile elements that spread horizontally between bacterial hosts and often confer adaptive phenotypes, including antimicrobial resistance (AMR). Theory suggests that opportunities for horizontal transmission favor plasmids with higher transfer rates, whereas selection for plasmid carriage favors less-mobile plasmids. However, little is known about the mechanisms leading to variation in transmission rates in natural plasmids or the resultant effects on their bacterial host. We investigated the evolution of AMR plasmids confronted with different immigration rates of susceptible hosts. Plasmid RP4 did not evolve in response to the manipulations, but plasmid R1 rapidly evolved up to 1,000-fold increased transfer rates in the presence of susceptible hosts. Most evolved plasmids also conferred on their hosts the ability to grow at high concentrations of antibiotics. This was because plasmids evolved greater copy numbers as a function of mutations in the copA gene controlling plasmid replication, causing both higher transfer rates and AMR. Reciprocally, plasmids with increased conjugation rates also evolved when selecting for high levels of AMR, despite the absence of susceptible hosts. Such correlated selection between plasmid transfer and AMR could increase the spread of AMR within populations and communities.

Tailoring CRISPR-Cas Immunity for the Degradation of Antibiotic Resistance Genes

“…As most of the ARGs are plasmid-borne (1,26), we focused on and evaluated VADER for eliminating ARGs on plasmids. We chose pBR322 as the target plasmid with a tetA gene conferring tetracycline resistance (Tet R ) and a bla gene conferring ampicillin resistance (Amp R ) (Figure 1C) .…”

“…Normally, mobilizable plasmids, such as RP4-2 and RK2, are low-copy plasmids with less than 10 copies in a cell. 30,33 As VADER managed to degrade ARG carried by a plasmid with a copy number up to 700, it shows sufficient capability for degradation of plasmid-borne ARGs. Furthermore, we tested whether tetA was actually degraded.…”

“…Then the following plasmids were generated in a streamlined method by inverse PCR with pEL01 as a template and programmable primer pairs to replace the spacer (Figure 1B). As most of the ARGs are plasmid-borne (1,26), we focused on and evaluated VADER for eliminating ARGs on plasmids. We chose pBR322 as the target plasmid with a tetA gene conferring tetracycline resistance (Tet R ) and a bla gene conferring ampicillin resistance (Amp R ) (Figure 1C).…”

Plasmid co-infection: linking biological mechanisms to ecological and evolutionary dynamics

“…Replication and partitioning systems impact a number of other model parameters indirectly, since they lead to a lower copy number of each plasmid variant in the co-infected cell. This can decrease the probability of successful conjugation ( q i ) [ 56 ] and plasmid cost ( ρ AB , γ AB ), compared to co-infection with compatible plasmids.…”

Introduction: the secret lives of microbial mobile genetic elements

“…The resulting pressures may not align with those acting on other regions of the genome, and can instead favour adaptations that can generate intragenomic conflicts [ 7 ]. For example, traits that promote selfish MGE transmission to other cells can impose a burden on the current host [ 8 , 9 ]. The evolutionary prospects of an autonomous MGE are thus not confined by the borders of the cell, and instead incorporate transmission across hosts and genetic backgrounds.…”