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Evolved plasmid-host interactions reduce plasmid interference cost.

ABSTRACT: Antibiotic selection drives adaptation of antibiotic resistance plasmids to new bacterial hosts, but the molecular mechanisms are still poorly understood. We previously showed that a broad-host-range plasmid was poorly maintained in Shewanella oneidensis, but rapidly adapted through mutations in the replication initiation gene trfA1. Here we examined if these mutations reduced the fitness cost of TrfA1, and whether this was due to changes in interaction with the host's DNA helicase DnaB. The strains expressing evolved TrfA1 variants showed a higher growth rate than those expressing ancestral TrfA1. The evolved TrfA1 variants showed a lower affinity to the helicase than ancestral TrfA1 and were no longer able to activate the helicase at the oriV without host DnaA. Moreover, persistence of the ancestral plasmid was increased upon overexpression of DnaB. Finally, the evolved TrfA1 variants generated higher plasmid copy numbers than ancestral TrfA1. The findings suggest that ancestral plasmid instability can at least partly be explained by titration of DnaB by TrfA1. Thus under antibiotic selection resistance plasmids can adapt to a novel bacterial host through partial loss of function mutations that simultaneously increase plasmid copy number and decrease unfavorably high affinity to one of the hosts' essential proteins.

SUBMITTER: Yano H

PROVIDER: S-EPMC5024541 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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Evolved plasmid-host interactions reduce plasmid interference cost.

Yano Hirokazu H Wegrzyn Katarznya K Loftie-Eaton Wesley W Johnson Jenny J Deckert Gail E GE Rogers Linda M LM Konieczny Igor I Top Eva M EM

Molecular microbiology 20160615 5

Antibiotic selection drives adaptation of antibiotic resistance plasmids to new bacterial hosts, but the molecular mechanisms are still poorly understood. We previously showed that a broad-host-range plasmid was poorly maintained in Shewanella oneidensis, but rapidly adapted through mutations in the replication initiation gene trfA1. Here we examined if these mutations reduced the fitness cost of TrfA1, and whether this was due to changes in interaction with the host's DNA helicase DnaB. The str ...[more]

PMID: 27121483

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Project description:UnlabelledPromiscuous plasmids replicate in a wide range of bacteria and therefore play a key role in the dissemination of various host-beneficial traits, including antibiotic resistance. Despite the medical relevance, little is known about the evolutionary dynamics through which drug resistance plasmids adapt to new hosts and thereby persist in the absence of antibiotics. We previously showed that the incompatibility group P-1 (IncP-1) minireplicon pMS0506 drastically improved its stability in novel host Shewanella oneidensis MR-1 after 1,000 generations under antibiotic selection for the plasmid. The only mutations found were those affecting the N terminus of the plasmid replication initiation protein TrfA1. Our aim in this study was to gain insight into the dynamics of plasmid evolution. Changes in stability and genotype frequencies of pMS0506 were monitored in evolving populations of MR-1 (pMS0506). Genotypes were determined by sequencing trfA1 amplicons from individual clones and by 454 pyrosequencing of whole plasmids from entire populations. Stability of pMS0506 drastically improved by generation 200. Many evolved plasmid genotypes with point mutations as well as in-frame and frameshift deletions and duplications in trfA1 were observed in all lineages with both sequencing methods. Strikingly, multiple genotypes were simultaneously present at high frequencies (>10%) in each population. Their relative abundances changed over time, but after 1,000 generations only one or two genotypes dominated the populations. This suggests that hosts with different plasmid genotypes were competing with each other, thus affecting the evolutionary trajectory. Plasmids can thus rapidly improve their stability, and clonal interference plays a significant role in plasmid-host adaptation dynamics.ImportancePromiscuous plasmids play an important role in the spread of antibiotic resistance and many other traits between closely and distantly related bacteria. However, little is known about the dynamics by which these broad-host-range antibiotic resistance plasmids adapt to novel bacteria and thereby become more persistent, even in the absence of antibiotics. In this study, we show that after no more than 200 generations of growth in the presence of antibiotics, a plasmid that was initially poorly maintained in a novel bacterial host evolved to become drastically more persistent in the absence of antibiotics. In each of the evolving populations, an unexpectedly large number of bacterial variants arose with distinct mutations in the plasmid's replication initiation protein. Our results suggest that clonal interference, characterized by competition between variant clones in a population, plays a major role in the evolution of the persistence of drug resistance.

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Evolved plasmid-host interactions reduce plasmid interference cost.

Publications

Evolved plasmid-host interactions reduce plasmid interference cost.

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