Genetic lineages and their traits in Neisseria meningitidis.

Neisseria meningitidis is a model organism for the study of bacterial population biology, for genome sequencing and pathogenicity research. In the recent years, our group has identified a variety of markers for hypervirulent lineages of meningococci, which in part could be validated for typing purposes. Furthermore, carrier strain collections of meningococci and N. lactamica were studied by multilocus sequence typing, and elucidated the impressive genetic variability of those species. Characterisation of meningococcal carrier strains allowed to define the capsule null locus (cnl) of meningococci, which frequently occurs among carrier isolates and renders strains constitutively unencapsulated. This finding poses the question about the yet unclear role of the meningococcal polysaccharide capsule in transmission and carriage. O-acetylation of the meningococcal polysaccharides is another variably expressed trait in meningococci. We identified the genes responsible for O-acetylation of the serogroup C, W-135 and Y capsules, and provided the genetic basis for understanding the variability of O-acetylation patterns in meningococci. The oatC and oatWY genes proved to be the first genes identified to be responsible for O-acetylation of polysialic acid.