Date of Award

Spring 2025

Project Type

Thesis

Program or Major

Microbiology

Degree Name

Master of Science

First Advisor

Cheryl A Whistler

Second Advisor

Richard G Smith

Abstract

Vibrio parahaemolyticus is a genetically diverse marine bacterium and the leading cause of seafood-borne bacterial illness in the United States. While most strains are harmless, some can cause illness. As oyster aquaculture grows in the Northeast, particularly in New Hampshire’s Great Bay Estuary (GBE), understanding the dynamics of V. parahaemolyticus population diversity and persistence is critical for public health and sustainable aquaculture production. This work investigates two major research questions: whether standard bacterial enumeration methods introduce bias when evaluating diversity of V. parahaemolyticus populations, and how environmental factors influence V. parahaemolyticus acquisition and microbiome development in juvenile oysters. We first tested two processing methods for isolation and enumeration of V. parahaemolyticus: Most Probable Number (MPN) enrichment and direct membrane filtration, which were compared for their ability to capture diversity in V. parahaemolyticus isolates from GBE water. While both methods produced similar proportions of unique sequence types, filtration captured significantly higher phylogenetic diversity and lower core genome conservation. We next examined how water source, temperature, and salinity influence the development of the oyster microbiome and acquisition/retention of V. parahaemolyticus. Through importation and simulated relay, we found that water source had the strongest effect on V. parahaemolyticus abundance, and the combination of high salinity and low temperature seawater was most effective at limiting pathogen abundance. Although treated hatchery water contained no detectable V. parahaemolyticus, it was detectable in oyster spat and algal feed. These results demonstrate that environmental conditions can potentially be manipulated to reduce the risk of V. parahaemolyticus acquisition in aquaculture settings. Together, these findings underscore the complexity of V. parahaemolyticus ecology and the usefulness of environmental approaches in oyster farming practice.

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