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Title: Resolving the plasmid paradox : costs and benefits of horizontal gene transfer in a community context
Author: Kottara, Anastasia
ISNI:       0000 0004 7428 2426
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2018
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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.
Supervisor: Brockhurst, Michael Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available