title: Haemophilus somnus possesses two systems for acquisition of transferrin-bound iron.
abstract: Haemophilus somnus strain 649 was found to acquire iron from ovine, bovine, and goat transferrins (Tfs). Expression of Tf receptors, as evaluated by solid-phase binding assays, required the organisms to be grown under iron-restricted conditions in the presence of Tf. Competition binding assays revealed the presence of two distinct Tf-binding receptor systems, one specific for bovine Tf and the other capable of binding all three ruminant Tfs. Affinity isolation procedures using total membranes yielded three putative bovine Tf-binding polypeptides and one putative ovine and goat Tf-binding polypeptide. PCR amplification followed by DNA sequence analyses revealed that H. somnus strain 649 possesses genes that encode a bipartite TbpA-TbpB receptor along with a homolog of the Histophilus ovis single-component TbpA receptor. Expression of TbpB and the single-component TbpA would appear to be subject to a form of phase variation involving homopolymeric nucleotide tracts within the structural genes.
authors.affiliation: Microbiology Unit, Department of Natural Resource Sciences, Macdonald Campus, McGill University, Ste. Anne de Bellevue, Quebec, Canada H9X 3V9.
authors.forename: Andrew
authors.initials: A
authors.lastname: Ekins
authors.forename: Fariborz
authors.initials: F
authors.lastname: Bahrami
authors.forename: Ada
authors.initials: A
authors.lastname: Sijercic
authors.forename: Deborah
authors.initials: D
authors.lastname: Maret
authors.forename: Donald F
authors.initials: DF
authors.lastname: Niven
mesh_terms: D000818:Animals; D001483:Base Sequence; D002417:Cattle; D044138:Haemophilus somnus / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D014168:Transferrin / Q000378:metabolism*; D033881:Transferrin-Binding Protein A / Q000737:chemistry / Q000302:isolation & purification; D033882:Transferrin-Binding Protein B / Q000737:chemistry / Q000302:isolation & purification
chemical_list: D014168:Transferrin; D033881:Transferrin-Binding Protein A; D033882:Transferrin-Binding Protein B; D007501:Iron