Author ORCID Identifier
Date of Graduation
Microbiology and Molecular Genetics
Doctor of Philosophy (PhD)
Nicholas De Lay
Bacteria are an integral part of human health and disease. In the human host, dental plaques form as a result of up to 700 individual bacterial species colonizing oral surfaces and forming a multispecies biofilm. These biofilms are the cause of prevalent human diseases such as dental caries, gingivitis, and periodontitis. The microbes present in the oral biofilm are highly spatially and temporally structured and require a primary colonizing species to adhere to host tissue. As an important primary colonizer of the oral biofilm, the actinobacterium Actinomyces oris utilizes cell wall anchored proteins and glycoconjugates to initiate adherence to host surfaces, recruit additional bacterial species that could not bind otherwise, and maintain the structural integrity of the oral biofilm. In this thesis, I reveal mechanisms involved in the assembly and display of surface proteins that are central to these processes in A. oris.
Cell wall-anchored proteins contain a signal peptide to direct their secretion to the exoplasmic side of the membrane, where they are liberated from the secretion machine by signal peptidases. Cell wall-anchored proteins also contain a cell wall sorting signal, which is required for their covalent attachment to peptidoglycan by transpeptidase enzymes called sortases. Furthermore, a subset of cell wall-anchored proteins are polymerized to form pili prior to being anchored. I found that pilin proteins require a distinct signal peptidase for their maturation and function and uncovered residues required for adherence in a minor pilin protein. In certain cases after translocation, proteins are modified by the addition of glycopolymers, and I characterized a phosphotransferase enzyme with a novel role in protein glycosylation. These studies contribute to the understanding of the role of A. oris as a primary colonizer in the oral biofilm. Additionally, using A. oris as a model for general processes has led to findings which are applicable to principles of biofilm formation, interspecies interactions, glycoconjugate formation, and bacterial pathogenesis.
Actinomyces oris, bacterial surface proteins, cell wall anchored proteins, pili, Gram positive pilus assembly, pathogenesis
Available for download on Thursday, September 12, 2019