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Duplication of pilus gene complexes of Haemophilus influenzae biogroup aegyptius
T D Read1, M Dowdell, S W Satola
1Veterans Affairs Medical Center, Department of Medicine, Emory University School of Medicine, Decatur, Georgia 30033, USA.
Abstract:
Brazilian purpuric fever (BPF) is a recently described pediatric septicemia caused by a strain of Haemophilus influenzae biogroup aegyptius. The pilus specified by this bacterium may be important in BPF pathogenesis, enhancing attachment to host tissue. Here, we report the cloning of two haf (for H. influenzae biogroup aegyptius fimbriae) gene clusters from a cosmid library of strain F3031. We sequenced a 6.8-kb segment of the haf1 cluster and identified five genes (hafA to hafE). The predicted protein products, HafA to HafD, are 72, 95, 98, and 90% similar, respectively, to HifA to HifD of the closely related H. influenzae type b pilus. Strikingly, the putative pilus adhesion, HifE, shares only 44% identity with HafE, suggesting that the proteins may differ in receptor specificity. Insertion of a mini-gammadelta transposon in the hafE gene eliminated hemadsorption. The nucleotide sequences of the haf1 and haf2 clusters are more than 99% identical. Using the recently published sequence of the H. influenzae Rd genome, we determined that the haf1 complex lies at a unique position in the chromosome between the pmbA gene and a hypothetical open reading frame, HI1153. The location of the haf2 cluster, inserted between the purE and pepN genes, is analogous to the hif genes on H. influenzae type b. BPF fimbrial phase switching appears to involve slip-strand mispairing of repeated dinucleotides in the pilus promoter. The BPF-associated H. influenzae biogroup aegyptius pilus system generally resembles other H. influenzae, but the possession of a second fimbrial gene cluster, which appears to have arisen by a recent duplication event, and the novel sequence of the HafE adhesin may be significant in the unusual pathogenesis of BPF.
Insights
Researchers cloned and sequenced two fimbrial gene clusters (haf) from Haemophilus influenzae biogroup aegyptius, identifying novel adhesin sequences potentially significant in Brazilian purpuric fever pathogenesis.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Brazilian purpuric fever (BPF) is a pediatric septicemia linked to Haemophilus influenzae biogroup aegyptius.
- Bacterial pili, particularly adhesins, are crucial for pathogen attachment and disease development.
Purpose of the Study:
- To clone and characterize the fimbrial gene clusters (haf) in H. influenzae biogroup aegyptius.
- To investigate the role of these genes in bacterial adherence and BPF pathogenesis.
Main Methods:
- Cosmid library construction and screening for haf gene clusters.
- DNA sequencing of the haf1 gene cluster (6.8 kb).
- Bioinformatic analysis comparing haf genes with known H. influenzae pilus genes.
- Gene disruption via mini-transposon insertion to assess hemadsorption.
Main Results:
- Two haf gene clusters, haf1 and haf2, were identified and cloned.
- Sequencing of haf1 revealed five genes (hafA-E) with predicted proteins similar to H. influenzae type b pilus proteins (HifA-D).
- The HafE adhesin showed only 44% identity to HifE, suggesting altered receptor specificity.
- Disruption of hafE abolished hemadsorption, confirming its role in adherence.
- haf1 and haf2 clusters showed >99% sequence identity, with haf2 located analogously to hif genes in H. influenzae type b.
- BPF fimbrial phase switching mechanism identified involving slip-strand mispairing.
Conclusions:
- The H. influenzae biogroup aegyptius pilus system shares similarities with other H. influenzae strains.
- The presence of a second fimbrial gene cluster, likely from recent duplication, and the unique HafE adhesin sequence may contribute to BPF's distinct pathogenesis.