B-292. Determining the Surface Components of the Type IV Secretion System in Neisseria gonorrhoeae and Neisseria meningitidis
A majority of Neisseria gonorrhoeae strains and a few Neisseria meningitidis strains encode a type IV secretion system (T4SS) similar to conjugation systems of the F-plasmid family. The gonococcal T4SS secretes single-stranded chromosomal DNA into the extracellular milieu where the secreted DNA is active in the transformation of other gonococci in the population. This T4SS is the only known system for the donation of DNA for natural transformation that does not involve cell lysis. To better understand the secretion mechanism and expression of the T4SS, we are working to identify surface components of this apparatus. Detection of these surface components would be useful for the identification of mutants defective in assembly or regulation of the T4SS. The T4SS encodes a putative pilin, TraA. DNA sequencing revealed the presence of three different traA alleles in the N. gonorrhoeae and N. meningitidis populations. This variation may indicate that TraA is surface exposed and subject to immune selection. Interestingly, TraA was not required for DNA secretion. The putative T4SS secretin TraK showed no sequence variation among gonococcal strains. TraK was found to interact with the putative outer membrane lipoprotein TraV, as shown using a bacterial two-hybrid method. Thus TraV and TraK likely form part of the secretion apparatus in the outer membrane. Using immunofluorescence microscopy, we found that antibodies to TraV only bound to a portion of the gonococci in the culture. These results suggest that the T4SS may be subject to phase variation in the gonococcal population. Furthermore, fluorescence was brighter at one portion of the cell, suggesting that the T4SS may be localized to the cell pole.