Characterization of the Francisella pathogenicity Island-encoded type VI secretion system and the development of a vaccine candidate

• Main Author: Duplantis, Barry Neil
• Other Authors: Nano, Francis E.
• Format: Thesis
• Language: English
• Published: 2011
• Subjects: Francisella; Temperature sensitive; Type VI secretion; Psychrophile; Vaccine; Arctic; Igla
• Online Access: http://hdl.handle.net/1828/3737

F. tularensis is a Gram-negative bacterial pathogen and it is the causative agent of tularemia. It has the ability to replicate to high numbers within a variety of host cells, including macrophages. Little is known of its virulence mechanisms; however, all species of Francisella contain a cluster of virulence genes known as the Francisella Pathogenicity Island (FPI), which is thought to encode a type 6 secretion system. While 14 of the 18 FPI genes encode products required for intracellular growth in macrophages, the functions of most of these proteins remain to be determined. Therefore, further work is required to understand the role played by the FPI in Francisella pathogenesis. In this thesis, the localization of the core FPI proteins IglA, IglB, IglC and IglD, was examined in order to further elucidate of the structure and activities of the FPI-encoded secretion system. Deletion mutagenesis of pdpA was performed to determine how host intracellular signalling might be affected by secretion of the putative FPI effector protein PdpA. In addition, variations in virulence between different biotypes of Francisella were investigated with respect to the role played by the FPI protein PdpD. Considering the highly infectious nature of Francisella and the absence of a quality vaccine, it is clear that this organism represents an excellent model for proof of principle investigations focussing on new vaccine technologies for intracellular pathogens. The second half of this thesis describes the construction and characterization of live attenuated temperature-sensitive vaccines. These vaccines were created in the intracellular pathogen F. novicida through allelic replacement of essential genes with naturally-occurring, cold-adapted, thermolabile homologues isolated from Arctic bacteria. Thus, the objectives of this work were twofold: to provide further characterization of the structural components and effector proteins associated with the FPI-encoded secretion system, and to develop a new and effective vaccine technology ...