In the meningitis belt of sub-Saharan Africa, there are cyclic meningococcal epidemics that coincide with clonal waves of Neisseria meningitidis carriage and invasive disease. In the framework of longitudinal colonization and disease studies in Ghana and Burkina Faso, meningococcal isolates belonging to the closely related hypervirulent A:ST-5, A:ST-7, and A:ST-2859 clones have been collected from 1998 to 2011 during meningococcal outbreaks. A comparative whole-genome sequencing study with 100 of these isolates identified the pilin glycosylation (pgl) locus as one hot spot of recombination. Frequent exchange of pgl genes in N. meningitidis by lateral gene transfer results in differences in the glycosylation patterns of pilin and other cell surface glycoproteins. In this study, we looked at both recombination and phase variation of the pgl genes of these clinical isolates and analyzed the glycan structures resulting from different pgl alleles and their variable expression. Our results indicate that the basal O-linked sugar of the glycans expressed by these isolates is masked by various additional mono- or disaccharide structures whose expression is highly variable due to the phase-variable expression of pgl genes. We also observed a distinct glycoform in two isolates with pgl loci that were modified by recombination. These data suggest that variation in N. meningitidis protein glycosylation could be crucial for bacterial adaptation to evade herd immunity in semi-immune populations. Investigating pilin glycosylation in N. meningitidis can shed light on the mechanisms by which this pathogen evades the host immune response, and may help identify potential targets for novel therapies and vaccines.
Keywords: meningitis; phase-variable expression; pilin glycosylation; whole-genome sequencing.