Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Microbiology and Immunology

Supervisor

Dr. Miguel Valvano

Abstract

Phosphorylation cascades governed by two-component signal transduction systems provide key signalling mechanisms in bacteria, simple eukaryotes and higher plants, allowing them to translate signals into adaptive responses. These regulatory pathways consist of a transmembrane sensor protein that responds to an environmental cue leading to autophosphorylation, followed by the transfer of the phosphate to a cytoplasmic response regulator. Here, I study AtsR, a membrane-bound hybrid sensor kinase of Burkholderia cenocepacia, that negatively regulates quorum sensing related virulence factors such as biofilm, type 6-secretion and protease secretion. B. cenocepacia is a Gram-negative opportunistic pathogen which causes severe, chronic respiratory infections in patients with cystic fibrosis and other immunocompromised conditions. This bacterium is also pathogenic in animal, plant, nematode, and insect infection models, and can survive within amoebae and macrophages. Presumably, the ability to survive in various niches requires adaptability to deal with changing environments. I hypothesize that AtsR is part of a multi-protein phosphorelay pathway which plays a critical role in regulation of niche adaptation and survival of B. cenocepacia in different hosts. In this thesis, I investigated AtsR function by characterizing the role of critical functional residues within the individual domains of AtsR and identify its cognate response regulator AtsT as a key component of the AtsR phosphorelay pathway. Furthermore, subsets of genes that are directly regulated by the AtsR cognate response regulator were identified by Chromatin immunoprecipitation followed by next generation sequencing (ChIP-Seq) analysis and its corresponding consensus DNA binding site is determined. I also investigated the role of AtsR as a global regulator of B. cenocepacia pathogenicity in the Arabidopsis thaliana and Galleria mellonella infection models.

Together, these studies identified a new regulatory network that highlights the importance of bacterial virulence and pathogenicity with careful consideration of the host. This work may provide an understanding at the molecular level of bacterial adaptation to ever changing niche environments.

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