Multiple neuB genes in Campylobacter jejuni

N-acetyl neuraminic acid (NANA) is a common constituent of C. jejuni lipooligosaccharide (LOS). Such structures often mimic gangliosides and are thought to be involved in the Guillain-Barre and Miller-Fisher syndromes following C. jejuni infection. Our analysis of the recently completed genome sequence of C. jejuni NCTC 11168 identified three putative N-acetyl neuraminic acid synthetase genes termed neuB1, neuB2 and neuB3. LOS from C. jejuni NCTC 11168 binds cholera toxin (CT) indicating the presence of NANA in a LOS structure mimicing the oligosaccharide portion of ganglioside GM1. Isogenic mutants were created in all three neuB genes and for one such mutant (neuB3) LOS was shown to have an increased mobility in SDS -PAGE gels and also failed to bind CT consistent with loss of a sialic acid residue from the structure. Heterologous expression of the neuB3 gene in E. coli demonstrated that NeuB3 was capable of in vitro NANA biosynthesis. The distribution of the neuB3 gene in C. jejuni strains with well characterised LOS was examined. Mutagenesis of neuB1 and neuB2 did not affect LOS, but neuB1 mutants were aflagellate and non-motile whereas no phenotype was evident for neuB2 mutants.