AN IRON-REGULATED OUTER-MEMBRANE PROTEIN-SPECIFIC TO BORDETELLA-BRONCHISEPTICA AND HOMOLOGOUS TO FERRIC SIDEROPHORE RECEPTORS

The bfrA (Bordetella bronchiseptica ferric iron repressed outer-membra ne protein) gene was cloned Bordetella bronchiseptica by screening a l ibrary of TnphoA insertion mutants for iron-repressed fusions to phoA. The bfrA gene encoded an 80 kDa outer-membrane protein with a high le vel of amino acid sequence identity to several bacterial proteins belo nging to the family of Ton B-dependent outer-membrane receptors. BfrA was especially homologous to Cir of Escherichia coli, IrgA of Vibrio c holerae and to three previously characterized ferric enterobactin rece ptors. DNA hybridization results indicated that bfrA was not present i n other Bordetella species. Expression of the bfrA gene was induced by low iron availability from a promoter overlapped by a sequence resemb ling a consensus Fur-binding sequence, and bfrA expression was derepre ssed in a B. bronchiseptica fur mutant. Utilization of the Bordetella siderophore alcaligin and the exogenous siderophore enterobactin was u naffected in bfrA mutants. Upon attempting to find the specificity of BfrA, 2,3-dihydroxybenzoylserine (DHBS) was shown to be utilized in a bfeA (Bordetella ferric enterobactin receptor gene)-dependent manner b y B. bronchiseptica and B. pertussis. In addition, the hydroxamate sid erophores ferrichrome and desferrioxamine B, and the iron source haemi n were shown to be utilized independently of bfeA and bfrA in B. bronc hiseptica and B. pertussis.