Transcriptional Regulation Paradigms of the Dual Host-Aquatic Lifestyle of Vibrio parahaemolyticus
Date
2024-08-09
Authors
Robinson, Oriana
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Abstract
Increased incidence of disease by marine pathogens correlates with rising sea surface
temperatures. These changing marine conditions have resulted in the geographic
expansion of pathogenic Vibrio spp. like Vibrio parahaemolyticus and increases in
temperature are driving large scale virulence priming, suggesting infectious Vibrio spp.
are in higher abundance in bivalve populations. As a result, the facultative pathogen V.
parahaemolyticus remains the causative agent of gastroenteritis from the consumption of
raw or undercooked seafood. This expansion is largely driven by the dual host-aquatic
lifestyle of V. parahaemolyticus where the bacterium employs numerous coordinated
mechanisms to survive and adapt across a broad range of niches. However, the
underlying genetic regulatory mechanisms that promote V. parahaemolyticus fitness
during its dual host-aquatic lifestyle remain poorly understood. Chitin catabolism is an
important contributor to the environmental survival of V. parahaemolyticus and previous
efforts to characterize the chitin catabolic cascade in V. parahaemolyticus using
transposon sequencing identified the transcriptional regulator VP1236 as a critical fitness
determinant for growth on chitin as a sole carbon source. Using a variety of phenotypic
assays, I characterized VP1236 as the central carbon metabolism regulator HexR and
explored the role of coordinated metabolism across cell morphology, biofilm formation,
carbon assimilation, and motility. The data revealed the significant role regulated carbon
metabolism plays in V. parahaemolyticus fitness in the aquatic environment. In contrast,
V. parahaemolyticus relies on many virulence factors during infection but the Type 3
Secretion Systems (T3SS) 1 and 2 remain critical virulence determinants. T3SS-1 is
present in all clinical and environmental isolates and contributes to host cell killing and
cytotoxicity. The expression of the T3SS-1 is coordinated by the transcriptional regulator
HlyU, which relieves a DNA cruciform, a non-B-DNA superstructure, to drive the
expression of the T3SS-1 master regulator exsA. However, HlyU also regulates numerous
other virulence factors in multiple pathogenic Vibrio spp. This global regulation of
virulence by HlyU prompted us to explore additional targets for HlyU in V.
parahaemolyticus. Using a chromatin-immunoprecipitation sequencing approach, I
investigated the global binding of HlyU in V. parahaemolyticus during infection. This
screen identified five putative targets for HlyU regulation which included a gene
encoding an extracellular endonuclease, exeM. Characterization of the exeM promoter
region for cruciform-forming elements identified two putative cruciform and
demonstrated HlyU-dependent regulation of activity. These results validate the developed
genomic screen for identifying HlyU-regulated targets and provide evidence for a DNA
cruciform in regulating gene expression in V. parahaemolyticus. Altogether,
investigations of the genetic regulatory mechanisms that support the dual host-aquatic
lifestyle of V. parahaemolyticus are crucial for understanding the impacts of foodborne
zoonosis to both human and marine organism health as climate change persists.
Description
Keywords
Bacteriology, Molecular Genetics, Microbial Genetics, Host-Pathogen Interactions, Bacterial Pathogenesis, Virulence, Vibrio parahaemolyticus, Chitin, Bacterial Fitness, Vibrio