White Rose University Consortium logo
University of Leeds logo University of Sheffield logo York University logo

Resolving the plasmid paradox: costs and benefits of horizontal gene transfer in a community context

Kottara, Anastasia (2018) Resolving the plasmid paradox: costs and benefits of horizontal gene transfer in a community context. PhD thesis, University of Sheffield.

[img] Text
Restricted until June 2020.

Request a copy


Horizontal gene transfer (HGT) is a central evolutionary process enhancing genome diversification and rapid adaptation of species to new environmental conditions. Mobile genetic elements (MGE) facilitate genetic exchange between species through HGT by carrying accessory gene cargos encoding beneficial traits such as resistance to metals and antibiotics. MGE-mediated transfer of antibiotic resistance genes between species in natural microbial communities has contributed to the global spread of antibiotic resistance. It is therefore essential to understand the ecological drivers of the maintenance and transmission of MGEs in bacterial communities. Here I use conjugative plasmids as an example MGE to study the ecological and evolutionary dynamics of plasmids in bacterial populations and communities across a range of environments. First, I demonstrate that plasmids selected in a single-host environment evolved host specialism due to fitness trade-offs, whereas plasmids evolved in a multi-host environment could overcome this trade-off to evolve host-generalism. Secondly, I show that the costs and benefits of plasmid carriage and the long-term dynamics of the plasmid and the mercury resistance transposon it encodes varied extensively between diverse species of Pseudomonas. I next show that plasmid maintenance was facilitated by compensatory evolution to ameliorate the cost of plasmid carriage. Compensatory loci varied between species, with parallel mutations targeting different regulatory and biosynthetic pathways in each species. Lastly, I examine the effect of community structure on plasmid dynamics in simple bacterial communities. When plasmids were carried by proficient plasmid-donor species this led to higher plasmid abundance at the community-level, while in diverse communities, plasmid transmission could be impeded through the dilution effect, limiting plasmid spread. This thesis demonstrates that plasmid dynamics in bacterial communities are determined by the combination of ecological and evolutionary processes, depending on the selective environment, the structure of the bacterial community and variation among species in their proficiency to host plasmids and to undergo compensatory evolution to ameliorate their costs. These data highlight the importance of studying plasmid dynamics in a community-context.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Science (Sheffield) > Animal and Plant Sciences (Sheffield)
Depositing User: Anastasia Kottara
Date Deposited: 28 Sep 2018 13:26
Last Modified: 28 Sep 2018 13:26
URI: http://etheses.whiterose.ac.uk/id/eprint/21545

Please use the 'Request a copy' link(s) above to request this thesis. This will be sent directly to someone who may authorise access.
You can contact us about this thesis. If you need to make a general enquiry, please see the Contact us page.

Actions (repository staff only: login required)