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Journal of Bacteriology, September 1998, p. 4693-4703, Vol. 180, No. 17
Division of Biological Sciences, University
of Missouri, Columbia, Missouri 652111;
Department of Biological Sciences, University of Zimbabwe,
Harare, Zimbabwe2;
Department of
Molecular Microbiology and Immunology, University of Missouri,
Columbia, Missouri 652123; and
Cancer
Research Center, Columbia, Missouri 652014
Received 23 February 1998/Accepted 10 June 1998
Haemophilus influenzae is a ubiquitous colonizer of the
human respiratory tract and causes diseases ranging from otitis media to meningitis. Many H. influenzae isolates express pili
(fimbriae), which mediate adherence to epithelial cells and facilitate
colonization. The pilus gene (hif) cluster of H. influenzae type b maps between purE and
pepN and resembles a pathogenicity island: it is present in
invasive strains, absent from the nonpathogenic Rd strain, and flanked
by direct repeats of sequence at the insertion site. To investigate the
evolution and role in pathogenesis of the hif cluster, we
compared the purE-pepN regions of various H. influenzae laboratory strains and clinical isolates. Unlike Rd,
most strains had an insert at this site, which usually was the only
chromosomal locus of hif DNA. The inserts are diverse in
length and organization: among 20 strains, nine different arrangements
were found. Several nontypeable isolates lack hif genes but
have two conserved open reading frames (hicA and
hicB) upstream of purE; their inferred products
are small proteins with no data bank homologs. Other isolates have
hif genes but lack hic DNA or have combinations of hif and hic genes. By comparing these
arrangements, we have reconstructed a hypothetical ancestral genotype,
the extended hif cluster. The hif region of
INT1, an invasive nontypeable isolate, resembles the hypothetical
ancestor. We propose that a progenitor strain acquired the extended
cluster by horizontal transfer and that other variants arose as
deletions. The structure of the hif cluster may correlate
with colonization site or pathogenicity.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Evolution of the Major Pilus Gene Cluster of
Haemophilus influenzae
*
Corresponding author. Mailing address: Division of
Biological Sciences, 110 Tucker Hall, University of Missouri, Columbia, MO 65211. Phone: (573) 882-9628. Fax: (573) 882-0123. E-mail: golomb{at}biosci.mbp.missouri.edu.
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