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ANNUAL CONFERENCE :: Abstract Library
Abstract Library
2004 Conference Abstract
| Type of Submission |
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Submission Type: |
Student Award - Poster Competition |
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Subject Category: |
Infection and Immunity |
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| Session Information |
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Presentation Date: |
June 23, 2004 |
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Abstract ID: |
SP11 |
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Session: |
Poster Session 3 |
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Time: |
15:00-16:30 |
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| Presenting Author |
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| Other Authors |
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D.F. NIVEN, McGill University
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| Title |
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Acquisition of haemoglobin-bound iron by Histophilus somni |
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| Abstract Text |
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The sheep pathogens, Histophilus ovis and Haemophilus agni, and the bovine pathogen, Haemophilus somnus, have now been assigned to a single species and renamed Histophilus somni. These organisms, like several other pathogens of the family Pasteurellaceae, require iron and are known to acquire iron from various transferrins by means of siderophore-independent, receptor-mediated mechanisms. The present communication deals with the acquisition of haemoglobin (Hb)-bound iron by five strains of H. somni, three of which (strains 649, 8025 and 2336) were referred to previously as H. somnus, and two (strains 9L and 3384Y), as H. ovis.
Growth assays revealed that while strain 649, and following a considerable lag phase, strains 8025 and 2336, can acquire iron from bovine Hb, but not from ovine, porcine or human Hb, strains 9L and 3384Y are unable to use any of these Hbs as iron sources for growth. The acquisition of Hb-bound iron by some other members of the Pasteurellaceae has been shown to involve homologues of the Hb-binding protein, HgbA, and using PCR approaches, we were able to identify and sequence hgbA homologues from strains 649, 9L and 3384Y. As in Pasteurella multocida, hgbA in H. somni was found to be preceded by hugX and hugZ and all three genes would appear to be arranged in an operon (hugXZ-hgbA). Interestingly, in both 9L and 3384Y, a 2-bp deletion in hgbA results in the introduction of a premature stop codon and offers a possible explanation for the lack of Hb utilization by these strains. Similarly, sequencing of a fragment of hgbA from strains 8025 and 2336 afforded a possible explanation for the considerable lag phases that were observed with these strains in the growth assays. In strain 649, this region contains a stretch of 6 Cs, a number that maintains the reading frame of the gene. In strains 8025 and 2336, however, the comparable regions were found to contain 10 Cs and 8 Cs, respectively, when the organisms were grown under iron-replete conditions and 9 Cs when the organisms were grown under iron-restricted conditions in the presence of bovine Hb. It would appear, therefore, that the extended lag phases reflect a form of phase variation and the selection of variants that can produce a functional HgbA.
It is concluded that the acquisition of Hb-bound iron by H. somni involves mechanisms analogous to those found in other members of the Pasteurellaceae. However, the specificities of the Hb receptors and the involvement of poly C tracts in phase variation are quite unusual.
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