Date of Award

Fall 2020

Project Type


Program or Major


Degree Name

Master of Science

First Advisor

Cheryl Whistler

Second Advisor

Stephen Jones

Third Advisor

Cheryl Andam


Vibrio parahaemolyticus is an emergent human pathogen that is the leading cause of seafood-borne bacterial infections in the United States and worldwide. Recently, clinical prevalence of V. parahaemolyticus has increased in the United States, especially from the North Atlantic Ocean. The majority of clinical isolates of V. parahaemolyticus harbor a hemolysin gene (tdh and/or trh) and a Type III Secretion System (T3SS)-containing mobile Vibrio Pathogenicity Island (VPaI). The VPaIs are evolutionary related yet distinct. These VPaIs include VPaIα (tdh+), VPaIβ (trh+), and a mosaic VPaIγ (tdh+/trh+). Strains harboring VPaIα cause the most infections globally, whose major effectors are known. In the United States, in particular from the North Atlantic, human infections with V. parahaemolyticus are predominantly caused by strains harboring the relatively uncharacterized VPaIγ. There are four major VPaIγ lineages in V. parahaemolyticus strains of North Atlantic, identified by the tdh allele they harbor. Strains harboring tdh3-VPaIγ are isolated most clinically, though strains harboring tdh5-VPaIγ are environmentally predominant. Using a dual approach of bioinformatics and bioassays, in this study we identify five novel T3SS2 effectors on VPaIγ. We provide evidence that suggests a V. parahaemolyticus population-based contribution towards its pathogenicity and environmental prevalence. Patterns of recombination in toxin orthologs from tdh3-VPaIγ and tdh5-VPaIγ indicate that the surrounding population is a major contributor to the content of these VPaIs. The divergence seen in these orthologs were assessed for contribution towards their effectiveness in pathogenesis or environmental fitness. Our predatory grazing assay suggests that one effector may have evolved for survival against eukaryotic predators in the environment. Utilizing bioassays to assess toxicity and virulence, we found evidence that four of the VPaIγ orthologs likely contribute to the tdh3-VPaIγ clinical prevalence. This work lays the foundation for understanding VPaIγ effector fitness benefits in relation to their environment and population.