Genetic diversity of three lgt loci for biosynthesis of lipooligosaccharide (LOS) in Neisseria species

Lipooligosaccharide (LOS) is a major virulence factor of the pathogenic Neisseria. Nine Igt genes at three chromosomal loci (Igt-1, 2, 3) encoding the glycosylltransferases responsible for the biosynthesis of LOS oligosaccharide chains were examined in 26 Neisseria meningitidis, 51 Neisseria gonorrhoeae and 18 commensal Neisseria strains. DNA hybridization, PCR and nucleotide sequence data were compared to previously reported Igt genes. Analysis of the genetic organization of the Igt loci revealed that in N. meningitidis, the Igt-1 and Igt-3 loci were hypervariable genomic regions, whereas the Igt-2 locus was conserved. In N. gonorrhoeae, no variability in the composition or organization of the three Igt loci was observed. Igt genes were detected only in some commensal Neisseria species. The genetic organization of the Igt-1 locus was classified into eight types and the Igt-3 locus was classified into four types. Two types of arrangement at Igt-1 (II and IV) and one type of arrangement at Igt-3 (IV) were novel genetic organizations reported in this study. Based on the three Igt loci, 10 LOS genotypes of N. meningitidis were distinguished. Phylogenetic analysis revealed a gene cluster, IgtH, which separated from the homologous genes IgtB and IgtE. The lgtH and IgtE genes were mutually exclusive and were located at the same position in Igt-1. The data demonstrated that pathogenic and commensal Neisseria share a common Igt gene pool and horizontal gene transfer appears to contribute to the genetic diversity of the Igt loci in Neisseria.