Abstract
The gram-negative bacterium Neisseria gonorrhoeae utilizes an O-linked glycosylation system to decorate a selected set of its proteins. So far however, no glycosylation associated phenotypes have been detected. The most abundant glycosylated protein in N. gonorrhoeae is PilE, the major pilin subunit of Type IV pili (Tfp). The expression of Tfp is associated with several phenotypes in this microbe such as attachment to the human cells, motility, agglutination, and finally horizontal gene transfer.
The major goal of this project was to investigate whether protein glycosylation played any role in the process of competence for natural transformation. There were three main reasons for exploring this possibility. First, the PilE protein in its assembled form is essential for DNA binding and uptake during transformation. Secondly, the PilE glycan is predicted to map on the surface of the type IV pilus and structural data and modelling have suggested that the pilus surface might be implicated in DNA binding. Third, the gram-negative pathogen Campylobacter jejuni also utilizes type IV pilus pilin-like proteins in transformation and the efficiency of this system is dramatically reduced in a mutant lacking its endogenous general protein glycosylation pathway. Here, I examined transformability in a variety of genetic backgrounds in which protein glycosylation was altered or abolished. In addition, transformability was also examined under a variety of conditions that altered the proficiency of competence. The latter included instances where key components of the type IV pilus were aberrantly expressed as well as experiments, where concentrations of transforming DNA were limiting. The possible effect phosphoethanolamine (PE) modification of PilE in conjunction with altered glycosylation status was also investigated. Despite all of these efforts, no significant alterations in transformation frequencies associated with the various glycosylation backgrounds and conditions were demonstrated. Thus, O-linked protein glycosylation appears to have no effect or influence on horizontal gene transfer in N. gonorrhoeae, at least not measured under these conditions investigated here.