| Summary: | Vibrio bacteria are commonly found in freshwater, marine, and estuarine environments. Members of this genus can exist in commensal relationships with marine animals or as planktonic bacteria, however, they are well known for their roles as pathogens towards humans and animals. In this dissertation, I investigated aspects of host-bacteria relationships with an emphasis on associations between Vibrio bacteria and oyster and human hosts. Vibriosis, a disease caused by Vibrio bacteria that affects shellfish, has been implicated in major losses of oyster larvae at aquaculture hatcheries. However, the species of Vibrio responsible for disease in aquaculture settings and specific virulence genes involved in disease are often variable or undefined. In my first research chapter, I sequenced the novel genomes of 45 hatchery-associated Vibrio isolates. I then characterized the virulence phenotypes of these Vibrio isolates towards Pacific oyster (Crassostrea gigas) larvae. Using comparative genomics and phylogenetic techniques, I find groups of orthologous genes associated with virulence and determine the phylogenetic relationships among pathogens and non-pathogens of C. gigas larvae. Vibrio coralliilyticus was the most common identification of the pathogenic isolates. A phylogenetic logistic regression model identified over 500 protein-coding genes correlated with pathogenicity. Many of these genes had straightforward links to disease encoding known pathogenesis mechanisms, including predicted hemolysins, proteases, and Type 3 Secretion Systems. Others, including chitin utilization genes, appear to have possible indirect roles in pathogenesis and may be more important for general survival in the host environment. Overall, these results highlight specific features that may enable Vibrio pathogen infection in C. gigas larvae. In my second research chapter, I analyzed the microbial communities at different points within a shellfish hatchery where C. gigas spat are produced. Understanding the overall dynamics of microbial ...
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