Regulation and export of alginate in Pseudomonas aeruginosa : a thesis presented in partial fulfilment of the requirements for the degree of Master of Doctor of Philosophy in Microbiology at Massey University

Abstract

Pseudomonas aeruginosa is a clinically important opportunistic human pathogen which is of particularly relevance to cystic fibrosis (CF) patients where P. aeruginosa pulmonary infections are the leading cause of both morbidity and mortality. The CF lung provides a unique environment to the pathogen which induces the overproduction of the exopolysaccharide alginate by the bacteria, resulting in a thick biofilm which protects the bacteria from the host immune response and antibiotic treatment, while contributing to the clogging of the lung. Furthermore, this switch from a non‐mucoid (minimal levels of alginate) to a mucoid (alginate over‐producing) phenotype is widely recognised as a poor prognosis indicator for patients, after which the infection cannot be eradicated. The exact mechanisms responsible for this switch are unclear but appear to involve a complex combination of transcriptional regulation, post translational regulation and the mutation of hyper‐mutable regions of the genome. This thesis investigates the physiological role of alginate for P. aeruginosa as well as several of the previously poorly understood steps in the biosynthesis and regulation of this important virulence factor. The outer membrane pore, AlgE, responsible translocation of alginate across the bacterial outer membrane was characterised. Interactions between two uncharacterised proteins, AlgK and AlgX, were identified and two novel regulatory networks involved in the control of alginate biosynthesis were identified.