The genetic bases for the variation in the lipo-oligosaccharide of the mucosal pathogen, Campylobacter jejuni -: Biosynthesis of sialylated ganglioside mimics in the core oligosaccharide

We have compared the lipo-oligosaccharide (LOS) biosynthesis loci from 11 Campylobacter jejuni strains expressing a total of 8 different ganglioside mimics in their LOS outer cores. Based on the organization of the genes, the 11 corresponding loci could be classified into three classes, with one of them being clearly an intermediate evolutionary step between the other two. Comparative genomics and expression of specific glycosyltransferases combined with in vitro activity assays allowed us to identify at least five distinct mechanisms that allow C. jejuni to vary the structure of the LOS outer core as follows: 1) different gene complements; 2) phase variation because of homopolymeric tracts; 3) gene inactivation by the deletion or insertion of a single base (without phase variation); 4) single mutation leading to the inactivation of a glycosyltransferase; and 5) single or multiple mutations leading to "allelic" glycosyltransferases with different acceptor specificities. The differences in the LOS outer core structures expressed by the 11 C. jejuni strains examined can be explained by one or more of the five mechanisms described in this work.