Novel particulate vaccine candidates recombinantly produced by pathogenic and nonpathogenic bacterial hosts : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Microbiology at Massey University, Manawatu, New Zealand.
Polyhydroxyalkanoates (PHAs) are biopolyesters synthesized as small spherical
cytoplasmic inclusion bodies by a range of bacteria. Recently, PHA beads have been
investigated for use as a vaccine delivery platform by using engineered heterologous
production hosts that allowed the efficient display of vaccine candidate antigens on the
beads surface and were found to greatly improve immunogenicity of the displayed
antigens. However, like other subunit vaccines, these antigen-displaying (vaccine) PHA
beads only provide a limited repertoire of antigens.
In this thesis we investigate the idea of directly utilizing the disease causative pathogen
or model organism to produce vaccine PHA beads with a large antigenic repertoire.
These beads are hypothesized to have the potential to induce greater protective
immunity compared to production of the same PHA bead in a heterologous production
This concept was exemplified with Pseudomonas aeruginosa and Mycobacterium
tuberculosis as model human pathogens. For P. aeruginosa we describe the engineering
of this bacterium to promote PHA and Psl (polysaccharide) production. This represents
a new mode of functional display for the engineering, production, and validation of a
novel OprI/F-AlgE fusion antigen-displayed on PHA beads. For the disease tuberculosis
we investigated the use of nonpathogenic M. smegmatis as a model organism for M.
tuberculosis. We described the bioengineering, production, and validation of Ag85AESAT-
6 displayed on PHA beads produced in M. smegmatis.
Here we showed that both organisms were harnessed to produce custom-made PHA
beads for use as particulate subunit vaccines that carried copurifying pathogen-derived
proteins as a large antigenic repertoire and the ability of these vaccine PHA beads to
generate a protective immune response.
This novel bioengineering concept of particulate subunit vaccine production could be
applied to a range of pathogens naturally producing PHA inclusions for developing
efficacious subunit vaccines for infectious diseases.