Date of Award

Spring 2011

Project Type

Dissertation

Program or Major

Microbiology

Degree Name

Doctor of Philosophy

First Advisor

Cheryl Whistler

Abstract

Vibrio parahaemolyticus is a poorly characterized human gastrointestinal pathogen whose virulence mechanisms are not well understood. Though closely related to Vibrio cholerae, V. parahaemolyticus infections are inflammatory and utilize virulence traits that are unique from the Cholera toxins yet remain poorly characterized. Vibrio spp. in general share an extensive core genome dedicated to environmental survival and unique, often horizontally acquired, gene content that is reserved for species specific lifestyles. This diversity has resulted in a genus of highly specialized bacteria partaking in dramatically different lifestyles ranging from symbiosis to pathogenesis. We propose that a comparative genomic and transcriptomic analysis of a conserved host association regulon (GacA) in the closely related V. fischeri (symbiont) and V. parahaemolyticus (pathogen), to exploit key lifestyle differences will expose genes that are unique to pathogenesis. In this study we identified a small, core regulon that is GacA activated comprised mostly of genes involved in central metabolism. Unique gene content in the V. parahaemolyticus GacA regulon contained both backbone and horizontally acquired elements that were activated or repressed in a highly selective fashion. Temperature was an important cue in virulence gene activation as determined through phenotypic and transcriptional assays and acted with GacA in an additive fashion. Specifically, expression of the classic virulence marker tdh was enhanced in a GacA mutant at 37°C; however the mutant was defective at initiating an infection in mice potentially discounting the relevance of TDH in disease. Though TDH is currently accepted as a clinical identifier, further work may be necessary to confirm a genuine correlation with disease causing strains. In addition, comparative genomics revealed a significant reorganization of the GacA regulon in V. parahaemolyticus suggesting that its control has been uncoupled from quorum sensing circuitry unlike in other characterized regulons. The GacA regulon of V. parahaemolyticus has undergone subtle regulatory changes resulting in GacA repression of select horizontally acquired elements and may serve as an ideal model of the evolution of regulatory networks and the emergence of novel virulence mechanisms.

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