The genetic basis of the phase variation repertoire of lipopolysaccharide immunotypes in Neisseria meningitidis.
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, IgtABE, 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 IgtA 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 Igt locus of strain 126E, an L1 immunotype strain, was cloned and sequenced, revealing two active genes, IgtC and IgtE. The remnants of the IgtA and IgtB genes and an inactive IgtD 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 Igt genes (ABCDE), and the recently reported IgtG gene, were used to determine the presence or absence of Igt 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 Igt 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 alpha-chain extension via IgtA or IgtC but cannot make beta-chain; the second group phase-vary the beta-chain extension via IgtG but do not vary alpha-chain (lacto-N-neotetraose).
Jennings
Michael P
MP
Department of Microbiology and Parasitology, The University of Queensland, Brisbane, QLD 4072, Australia1.
Srikhanta
Yogitha N
YN
Department of Microbiology and Parasitology, The University of Queensland, Brisbane, QLD 4072, Australia1.
Moxon
E Richard
ER
University of Oxford, Department of Paediatrics, Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, UK2.
Kramer
Marco
M
National Institute of Public Health and Environmental Protection, Bilthoven, The Netherlands3.
Poolman
Jan T
JT
National Institute of Public Health and Environmental Protection, Bilthoven, The Netherlands3.
Kuipers
Betsy
B
National Institute of Public Health and Environmental Protection, Bilthoven, The Netherlands3.
van der Ley
Peter
P
National Institute of Public Health and Environmental Protection, Bilthoven, The Netherlands3.
D001426:Bacterial Proteins; D001483:Base Sequence; D015139:Blotting, Southern; D004269:DNA, Bacterial / Q000032:analysis; D005798:Genes, Bacterial / Q000235:genetics*; D014644:Genetic Variation; D005964:Glucosyltransferases / Q000235:genetics*; D016695:Glycosyltransferases / Q000235:genetics; D008070:Lipopolysaccharides / Q000378:metabolism*; D008969:Molecular Sequence Data; D017351:N-Acetylglucosaminyltransferases / Q000235:genetics*; D009345:Neisseria meningitidis / Q000235:genetics*; D009844:Oligosaccharides / Q000235:genetics; D016133:Polymerase Chain Reaction; D020079:Terminal Repeat Sequences / Q000235:genetics
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D008070:Lipopolysaccharides; D009844:Oligosaccharides; C013084:lacto-N-neotetraose; D016695:Glycosyltransferases; C101829:LgtC protein, Neisseria; D005964:Glucosyltransferases; C401409:LgtA protein, bacteria; D017351:N-Acetylglucosaminyltransferases; C114421:lipooligosaccharide beta chain synthesizing glucosyltransferase