The type IV secretion systems of Neisseria gonorrhoeae

PhD ceremony: Ms. E. Pachulec, 11.00 uur, Academiegebouw, Broerstraat 5, Groningen

Thesis: The type IV secretion systems of Neisseria gonorrhoeae

Promotor(s): prof. A.J.M. Driessen

Faculty: Mathematics and Natural Sciences

Neisseria gonorrhoeae is a human pathogen causing gonorrhea, the second most common sexually transmitted disease in the world. The rapid spread of antibiotic resistance in gonoccoci has resulted in strains that are more and more resistant to the available antibiotics treatment. Highly efficient gene transfer is among others mediated by Type IV secretion systems (T4SSs). These T4SSs are multiprotein complexes used by many pathogenic bacteria to deliver DNA and/or virulence factors into host cells. Two gonococcal T4SSs have been the subject of the thesis of Emilia Pachulec.

The first T4SS is encoded in a chromosomal genetic island (GGI). This unique system is used by gonoccoci to secrete DNA for transformation. The components of the mating pair formation complex display homology to the F plasmid conjugative T4SS while proteins involved in DNA processing for transfer show similarity to those found in genomic islands and integrating conjugative elements. Mutational analysis of genes encoded by the GGI was performed and the minimal genetic composition of the island necessary for DNA secretion was determined by Pachulec. She found that DNA secretion by gonoccoci occurs only in the presence of defective pilin assembly system. The second T4SS is encoded by the conjugative gonococcal plasmids. The complete nucleotide sequence of the Dutch type tetracycline conjugative plasmid has been determined. Sequence analysis showed that gonoccocal plasmids belong to a novel IncP1 subfamily and display exceptional features not identified yet in any other plasmids. The transfer mediated by both gonococcal T4SSs occurs independently.