The tri-trophic interaction of plants, pathogenic bacteria and bacteriophages
Meaden, Sean McClarey
Date: 27 November 2015
Publisher
University of Exeter
Degree Title
PhD in Biological Sciences
Abstract
The ecology and evolution of pathogens are key factors in predicting the
severity and spread of disease, as well as treatment outcomes. However, the
effects of multiple trophic levels that include host, microbial competitors and
viruses are typically overlooked. In this thesis I develop our understanding of
bacteria-phage coevolution, ...
The ecology and evolution of pathogens are key factors in predicting the
severity and spread of disease, as well as treatment outcomes. However, the
effects of multiple trophic levels that include host, microbial competitors and
viruses are typically overlooked. In this thesis I develop our understanding of
bacteria-phage coevolution, microbial dispersal and the role of the
microbiome in disease. The results of these experiments have direct
implications for phage therapy: the use of bacteriophages to treat bacterial
infections. Firstly, I explore the risks of phage application in the environment
and draw parallels with the misuse of antibiotics in selecting for bacterial
resistance. I then demonstrate that the evolution of resistance to phages in a
plant pathogenic bacterium is context-dependent. Notably, I find a fitness cost
in plant infections that is absent when the bacteria are cultured solely in the
laboratory. I then characterize four novel phages and use a simple laboratory
based assay to predict their potential as phage therapy agents in an
agricultural context. Next I show that reservoir species of plant hosts can
affect the evolution of virulence, when bacteria are passaged on both a focal
and distant host, but find no evidence of local adaptation. I also show that the
evolution of such traits can occur in a parallel manner at the genetic level. I
then determine a compositional shift in the microbiota associated with the
symptoms of bleeding canker disease in Horse Chestnut trees across the
length of the UK. Finally, I find an age-related decline in bacterial species
richness and evidence for niche-assembly theories by investigating bacterial
dispersal in UK Oak trees in a single woodland.
Doctoral Theses
Doctoral College
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