Type IV secretion in Neisseria gonorrhoeae: Its role in DNA secretion and in bacteria-host cell interactions.

摘要

Neisseria gonorrhoeae, the etiologic agent of the sexually transmitted disease gonorrhea, is a gram-negative, obligate, human pathogen. Previous research demonstrated that 80% of N. gonorrhoeae strains contain the gonococcal genetic island (GGI). This thesis describes the development of a method for cloning and rapid1y mutagenizing the GGI, its sequence analysis and the phenotypes of GGI gene mutants in type IV secretion of DNA, and the role of the GGI in interactions with the host.; The GGI was cloned using insertion-duplication mutagenesis and multiple mutants were constructed. Mutation and examination of the type IV secretion system (T4SS) gene homologues demonstrated a role for the GGI in secretion of DNA into the extracellular milieu. Furthermore, secreted DNA could transform recipient gonococci. Sequence analysis of the GGI revealed many characteristics of pathogenicity islands, suggesting that it was horizontally acquired by the gonococcus at some point in its evolutionary history. Additionally, the GGI-encoded T4SS bears resemblance to the conjugation system of Escherichia coli F-plasmid. The GGI encodes nineteen homologues of T4SS proteins and an additional six homologues of DNA processing proteins.; Previous studies had shown that certain forms of the GGI were associated with a more serious complication of gonococcal disease, disseminated gonococcal infection. Additionally, many bacterial pathogens utilize T4SSs for the establishment of disease in the host. These observations suggested that the GGI might have a role in disease. Analysis of GGI mutants during infection of primary human cervical cells revealed an altered interaction with the host cells; GGI mutants were delayed in adherence and displayed an aggregation phenotype. Further experiments demonstrated a role for DNA in wild type infection.; Taken together, this research establishes that the GGI and its encoded T4SS play a role in DNA secretion and in host interactions. Secretion of DNA by the gonococcus may be a mechanism by which the gonococcus mediates exchange of alleles for antigenic variation, and it may contribute to the growing problem of antibiotic resistance in N. gonorrhoeae. Further studies may elucidate the mechanisms by which secreted DNA and the T4SS affect gonococcal interactions with the host.