Defense Date

2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Microbiology & Immunology

First Advisor

Cynthia Nau Cornelissen

Abstract

Neisseria gonorrhoeae is an obligate human pathogen that causes the common sexually- transmitted infection, gonorrhea. Gonococcal infections cause significant morbidity, particularly among women, as the organism ascends to the upper reproductive tract, resulting in pelvic inflammatory disease, ectopic pregnancy and infertility. Antibiotic resistance rates have risen dramatically, leading to severe restriction of treatment options for gonococcal disease. Gonococcal infections do not elicit protective immunity nor is there an effective vaccine to prevent the disease. Thus, further characterization of expression, function and regulation of surface antigens could lead to better treatment and prevention modalities in the future. N. gonorrhoeae express a repertoire of TonB-dependent transporters for the acquisition of iron. All of these transporters are under the transcriptional regulation of Fur. We investigated putative intracellular iron sources utilized by gonococci and the role that the TonB-dependent transporter, TdfF, played in this acquisition. We determined that ascorbate which could prevent ferritin degradation or withhold iron from gonococci, inhibited intracellular survival. The utilization of iron from the iron binding moiety 2, 5-DHBA of the putative mammalian siderophore was also examined. In this study we continued to investigate the regulation of TdfF and further investigate potential host-specific inducing molecules for TdfF expression. We investigated the regulation of tdfF expression and the role of MpeR, an AraC-like regulator, in tdfF expression. We determined that MpeR, interacted specifically with the DNA sequence upstream of fetA and activated FetA expression. We confirmed that the outer membrane transporter, FetA, allows gonococcal strain FA1090 to utilize the xenosiderophore, ferric-enterobactin, as an iron source. However, we further demonstrated that FetA has an extended range of substrates that encompasses other catecholate xenosiderophores, including ferric-salmochelin and the dimers and trimers of dihydroxybenzoylserine. We demonstrated that fetA is encoded as part of an iron-repressed, MpeR-activated operon, which putatively encodes other iron transport proteins. These iron transport proteins also play a role in xenosiderophore acquisition. We also identified genetic differences that may explain why some gonococcal strains are capable of xenosiderophore internalization in a TonB-dependent pathway and other strains are restricted to TonB-independent pathways. Interestingly, the chromosomal locus that codes for mpeR and tdfF is pathogen specific. Thus understanding more about the TonB-dependent transporter and AraC-like regulator may further elucidate the pathogenicity of N gonorrhoeae.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

September 2011

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