The incidence of gonorrhoea is increasing at an alarming pace, and therapeutic options continue to narrow as a result of worsening drug resistance. Neisseria gonorrhoeae is naturally competent, allowing the organism to adapt rapidly to selection pressures including antibiotics. A sub-population of N. gonorrhoeae carries the Gonococcal Genetic Island (GGI), which encodes a type IV secretion system (T4SS) that secretes chromosomal DNA. Previous research has shown that the GGI increases transformation efficiency in vitro, but the extent to which it contributes to horizontal gene transfer (HGT) during infection is unknown. Here we analysed genomic data from clinical isolates of N. gonorrhoeae to better characterize GGI+ and GGI- sub-populations and to delineate patterns of variation at the locus itself. We found the element segregating at an intermediate frequency (61%), and it appears to act as a mobile genetic element with examples of gain, loss, exchange and intra-locus recombination within our sample. We further found evidence suggesting that GGI+ and GGI- sub-populations preferentially inhabit distinct niches with different opportunities for HGT. Previously, GGI+ isolates were reported to be associated with more severe clinical infections, and our results suggest this could be related to metal-ion trafficking and biofilm formation. The co-segregation of GGI+ and GGI- isolates despite mobility of the element suggests that both niches inhabited by N. gonorrhoeae remain important to its overall persistence as has been demonstrated previously for cervical- and urethral-adapted sub-populations. These data emphasize the complex population structure of N. gonorrhoeae and its capacity to adapt to diverse niches.
Keywords: Gonococcal Genetic Island (GGI); Neisseria gonorrhoeae; pangenome; population genetics.