The genetic basis of the phase variation repertoire of lipopolysaccharide immunotypes in Neisseria meningitidis The GenBank accession number for the sequence reported in this paper is U65788.

Abstract

Neisseria meningitidis strains express a diverse range of lipopolysaccharide (LPS) structures that have been classified into 12 immunotypes. A feature of meningococcal LPS is the reversible, high-frequency switching of expression (phase variation) of terminal LPS structures. A number of studies are strongly suggestive of a key role for these terminal structures, and their phase-variable expression, in pathogenesis. In a previous study, a locus of three LPS biosynthetic genes, lgtABE, involved in the biosynthesis of one of these terminal structures, lacto-N-neotetraose, was described. The molecular mechanism of phase-variable expression of this structure is by high-frequency mutation in a homopolymeric tract of G residues in the lgtA gene. To investigate the genetic basis of the structural differences between the immunotypes, and the potential for strains to express alternative immunotypes, this locus was examined in all of the immunotype strains. Initially, the lgt locus of strain 126E, an L1 immunotype strain, was cloned and sequenced, revealing two active genes, lgtC and lgtE. The remnants of the lgtA and lgtB genes and an inactive lgtD gene were also present, indicating that the locus may have once contained five active genes, similar to a locus previously reported in Neisseria gonorrhoeae strain F62. Probes based on each of the lgt genes (ABCDE), and the recently reported lgtG gene, were used to determine the presence or absence of lgt genes within individual strains, allowing the prediction of the phase variation repertoire of these strains. Sequencing to determine the nature of homopolymeric tract regions within the lgt genes was carried out to establish the potential for LPS switching. In general, the set of strains examined could be sorted into two distinct groups : one group which phase-vary the α-chain extension via lgtA or lgtC but cannot make β-chain; the second group phase-vary the β-chain extension via lgtG but do not vary α-chain (lacto-N-neotetraose).

Epidemiology, hypermutation, within–host evolution and the virulence ofNeisseria meningitidis

“…Whereas capsules prevent desiccation during open-air transmission and make the bacteria less vulnerable to phagocytosis in the blood, they also reduce the likelihood of N. meningitidis invading the cells of the epithelia (Hammerschmidt et al 1996;de Vries et al 1996). Sialylated LPS play a dual role in evading host immunity in the blood and facilitating entry into epithelial cells (de Vries et al 1996;Jennings et al 1999 L8 LPS are favoured in the epithelia and sub-epithelia. In addition, in the blood, capsulated N. meningitidis with assembled pili and L3, L9 and L7 LPS have an advantage.…”

Involvement of genes of genome maintenance in the regulation of phase variation frequencies in Neisseria meningitidis

“…These genes are often referred to as contingency loci . Phase variable expression has been experimentally demonstrated for surface antigens such as opacity proteins, lipopolysaccharides, capsular polysaccharides, pili, haemoglobin receptors, PorA and Opc outer-membrane proteins, a putative protease and the NadA adhesin (de Vries et al, 1996;Jennings et al, 1998Jennings et al, , 1999Hammerschmidt et al, 1996;Jonsson et al, 1991;Lewis et al, 1999;Richardson & Stojiljkovic,1999;van der Ende et al, 2000;Sarkari et al, 1994;Martin et al, 2003). We recently showed that 47 genes were likely to be regulated by such a mechanism in N. meningitidis strain MC58 (Martin et al, 2003).…”

Protozoan predation, diversifying selection, and the evolution of antigenic diversity in Salmonella

“…One important example is LPS phase variation by means of contingency loci that allows these bacteria to express different LPS molecules after every generation, enhancing their ability to survive and escape host immune cell recognition (23,24,27). Thus, strong selective pressure from the immune system during bacterial invasion is believed to be the driving force of LPS variation among these bacteria.…”

“…Bacterial survival within the host's blood stream depends on the ability to escape the innate and adaptive immune systems, and H. influenza and N. meningitidis both have multiple genes under control of phase variation that result in antigenic variants arising every generation, allowing for immune evasion (20)(21)(22)(23)(24)(25)(26)(27)(28). One important example is LPS phase variation by means of contingency loci that allows these bacteria to express different LPS molecules after every generation, enhancing their ability to survive and escape host immune cell recognition (23,24,27).…”