Transcriptional Regulation Paradigms of the Dual Host-Aquatic Lifestyle of Vibrio parahaemolyticus

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.