title: exl, an exchangeable genetic island in Neisseria meningitidis.
abstract: The genetic structure and evolution of a novel exchangeable meningococcal genomic island was defined for the important human pathogen Neisseria meningitidis. In 125 meningococcal strains tested, one of three unrelated nucleotide sequences, designated exl (exchangeable locus), was found between a gene required for heme utilization, hemO, and col, encoding a putative Escherichia coli collagenase homologue. The 5' boundary of each exl cassette was the stop codon of hemO, whereas the 3' boundary was delineated by a 33-bp repeat containing neisserial uptake sequences located downstream of col. One of the three alternative exl cassettes contained the meningococcal hemoglobin receptor gene, hmbR (exl3). In other meningococcal strains, hmbR was absent from the genome and was replaced by either a nucleotide sequence containing a novel open reading frame, exl2, or a cassette containing exl3. The proteins encoded by exl2 and exl3 had no significant amino acid homology to HmbR but contained six motifs that are also present in the lipoprotein components of the lactoferrin (LbpB), transferrin (TbpB), and hemoglobin-haptoglobin (HpuA) uptake systems. To determine the evolutionary relationships among meningococci carrying hmbR, exl2, or exl3, isolates representing 92 electrophoretic types were examined. hmbR was found throughout the population structure of N. meningitidis (genetic distance, >0.425), whereas exl2 and exl3 were found in clonal groups at genetic distances of <0.2. The commensal neisserial species were identified as reservoirs for all of the exl cassettes found in meningococci. The structure of these cassettes and their correlation with clonal groups emphasize the extensive gene pool and frequent horizontal DNA transfer events that contribute to the evolution and virulence of N. meningitidis.
authors.affiliation: Department of Medicine and Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, USA. charlene.kahler@monash.edu.au
authors.forename: C M
authors.initials: CM
authors.lastname: Kahler
authors.forename: E
authors.initials: E
authors.lastname: Blum
authors.forename: Y K
authors.initials: YK
authors.lastname: Miller
authors.forename: D
authors.initials: D
authors.lastname: Ryan
authors.forename: T
authors.initials: T
authors.lastname: Popovic
authors.forename: D S
authors.initials: DS
authors.lastname: Stephens
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D018070:Biological Specimen Banks; D002352:Carrier Proteins / Q000235:genetics; D004251:DNA Transposable Elements / Q000235:genetics*; D019143:Evolution, Molecular; D022761:Gene Transfer, Horizontal; D006419:Heme Oxygenase (Decyclizing); D006801:Humans; D033862:Iron-Binding Proteins; D008589:Meningococcal Infections / Q000382:microbiology; D008969:Molecular Sequence Data; D009345:Neisseria meningitidis / Q000145:classification / Q000235:genetics* / Q000472:pathogenicity; D011110:Polymorphism, Genetic; D011956:Receptors, Cell Surface / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D012703:Serotyping; D033863:Transferrin-Binding Proteins
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D004251:DNA Transposable Elements; C094109:HmbR protein, Neisseria meningitidis; D033862:Iron-Binding Proteins; D011956:Receptors, Cell Surface; D033863:Transferrin-Binding Proteins; C423452:HemO protein, Neisseria meningitidis; D006419:Heme Oxygenase (Decyclizing)