Exploring the role of diversity in bacteria-phage ecology and evolution
Common, J
Date: 29 March 2021
Publisher
University of Exeter
Degree Title
PhD in Biological Sciences
Abstract
Host diversity is one of the key factors that determine why pathogens can emerge and cause epidemics, the scale of an epidemic, and host-pathogen coevolution. Although the effects of host diversity on pathogen spread are well-described, we currently lack a detailed understanding of the ecological and evolutionary mechanisms that underpin ...
Host diversity is one of the key factors that determine why pathogens can emerge and cause epidemics, the scale of an epidemic, and host-pathogen coevolution. Although the effects of host diversity on pathogen spread are well-described, we currently lack a detailed understanding of the ecological and evolutionary mechanisms that underpin them. The interactions between phage and bacteria with a CRISPR-Cas immune system are a tractable model system to study how host density and genetic diversity impacts phage epidemiology, evolution and coevolution between the host and the phage. In this thesis, I first summarize existing literature on the role of host genetic diversity on host-parasite interactions. I then present experiments that explore how population bottlenecks, which impact both host density and genetic diversity, affect the epidemiology and evolution of phage. I find that bottlenecks result in more rapid phage extinction, which is driven primarily by the changes in host density. Next, I explore how manipulations of host genetic diversity alter the epidemiology and evolution of a phage that can infect a single host genotype in the population. I find that greater diversity results in protection of the susceptible host due to reduced contact rates with phage. I also find evidence for interaction between host diversity, phage population size, and the likelihood of phage evolution. Finally, I examine the coevolutionary interaction between phage and bacteria with CRISPR immune systems. I find that bacterial populations initially evolve diversity in their CRISPR-Cas immune systems that is sufficiently low for an escalating arms-race dynamic to ensue, that lasts until diversity in the CRISPR-Cas resistance alleles becomes too high, causing phage extinction.
Doctoral Theses
Doctoral College
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