An iron-regulated outer-membrane protein specific to Bordetella bronchiseptica and homologous to ferric siderophore receptors

Abstract

The bfrA (Bordetella bronchiseptica ferric iron repressed outer-membrane protein) gene was cloned from Bordetella bronchiseptica by screening a library of TnphoA insertion mutants for iron-repressed fusions to phoA. The bfrA gene encoded an 80 kDa outer-membrane protein with a high level of amino acid sequence identity to several bacterial proteins belonging to the family of Ton B-dependent outer-membrane receptors. BfrA was especially homologous to Cir of Escherichia coli, IrgA of Vibrio cholerae and to three previously characterized ferric enterobactin receptors. DNA hybridization results indicated that bfrA was not present in other Bordetella species. Expression of the bfrA gene was induced by low iron availability from a promoter overlapped by a sequence resembling a consensus Fur-binding sequence, and bfrA expression was derepressed in a B. bronchiseptica fur mutant. Utilization of the Bordetella siderophore alcaligin and the exogenous siderophore enterobactin was unaffected 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 by B. bronchiseptica and B. pertussis. In addition, the hydroxamate siderophores ferrichrome and desferrioxamine B, and the iron source haemin were shown to be utilized independently of bfeA and bfrA in B. bronchiseptica and B. pertussis.