Functional analysis of the Gonococcal Genetic Island of Neisseria gonorrhoeae

Neisseria gonorrhoeae is an obligate human pathogen that is responsible for the sexually-transmitted disease gonorrhea. N. gonorrhoeae encodes a T4SS within the Gonococcal Genetic Island (GGI), which secretes ssDNA directly into the external milieu. Type IV secretion systems (T4SSs) play a role in horizontal gene transfer and delivery of effector molecules into target cells. We demonstrate that GGI-like T4SSs are present in other β-proteobacteria, as well as in α- and γ-proteobacteria. Sequence comparison of GGI-like T4SSs reveals that the GGI-like T4SSs form a highly conserved unit that can be found located both on chromosomes and on plasmids. To better understand the mechanism of DNA secretion by N. gonorrhoeae, we performed mutagenesis of all genes encoded within the GGI, and studied the effects of these mutations on DNA secretion. We show that genes required for DNA secretion are encoded within the yaa-atlA and parA-parB regions, while genes encoded in the yfeB-exp1 region could be deleted without any effect on DNA secretion. Genes essential for DNA secretion are encoded within at least four different operons.