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Infection and Immunity, March 2001, p. 1687-1696, Vol. 69, No. 3
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.3.1687-1696.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

exl, an Exchangeable Genetic Island in Neisseria meningitidis

C. M. Kahler,*,1,2 E. Blum,1,2 Y. K. Miller,1,2 D. Ryan,2,3 T. Popovic,4 and D. S. Stephens1,2

Department of Medicine and Department of Microbiology and Immunology, Emory University School of Medicine,1 Research Service, VA Medical Center,2 and Centers for Disease Control and Prevention,4 Atlanta, and State University of West Georgia, Carrollton,3 Georgia

Received 6 September 2000/Returned for modification 5 October 2000/Accepted 27 November 2000

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.

* Corresponding author. Present address: Department of Microbiology, Monash University, Wellington Rd., Clayton 3800, Australia. Phone: 03/99054842. Fax: 03/99054811. E-mail: charlene.kahler{at}monash.edu.au.

Infection and Immunity, March 2001, p. 1687-1696, Vol. 69, No. 3
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.3.1687-1696.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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