IRON, A NOVEL OUTER-MEMBRANE SIDEROPHORE RECEPTOR CHARACTERISTIC OF SALMONELLA-ENTERICA

Speciation in enterobacteria involved horizontal gene transfer, Theref ore, analysis of genes acquired by horizontal transfer that are presen t in one species but not its close relatives is expected to give insig hts into how new bacterial species were formed, In this study we chara cterize iroN, a gene located downstream of the iroBC operon in the iro A locus of Salmonella enterica serotype Typhi. Like iroBC, the iroN ge ne is present in all phylogenetic lineages of S. enterica but is absen t from closely related species such as Salmonella bongori or Escherich ia coli, Comparison of the deduced amino acid sequence of iroN with ot her proteins suggested that this gene encodes an outer membrane sidero phore receptor protein, Mutational analysis in S. enterica and express ion in E. coli identified a 78-kDa outer membrane protein as the iroN gene product, When introduced into an E. coli fepA cir fiu aroB mutant on a cosmid, iroN mediated utilization of structurally related catech olate siderophores, including N-(2,3-dihydroxybenzoyl)-L-serine, myxoc helin A, benzaldehyde-2,3-dihydroxybenzhydrazone, zoyl)-L-2-N,6-N-bis( 2,3-dihydroxybenzoyl)-L-lysine amide, and enterochelin, These results suggest that the iroA locus functions in iron acquisition in S. enteri ca.