title: The Bradyrhizobium japonicum fegA gene encodes an iron-regulated outer membrane protein with similarity to hydroxamate-type siderophore receptors.
abstract: Iron is important in the symbiosis between soybean and its nitrogen-fixing endosymbiont Bradyrhizobium japonicum, yet little is known about rhizobial iron acquisition strategies. Analysis of outer membrane proteins (OMPs) from B. japonicum 61A152 identified three iron-regulated OMPs in the size range of several known receptors for Fe(III)-scavenging siderophores. One of the iron-regulated proteins, FegA, was purified and microsequenced, and a reverse genetics approach was used to clone a fegA-containing DNA fragment. Sequencing of this fragment revealed a single open reading frame of 750 amino acids. A putative N-terminal signal sequence of 14 amino acids which would result in a mature protein of 736 amino acids with a molecular mass of 80,851 Da was predicted. FegA shares significant amino acid similarity with several Fe(III)-siderophore receptors from gram-negative bacteria and has greater than 50% amino acid similarity and 33% amino acid identity with two [corrected] bacterial receptors for hydroxamate-type Fe(III)-siderophores. A dendrogram describing total inferred sequence similarity among 36 TonB-dependent OMPs was constructed; FegA grouped with Fe(III)-hydroxamate receptors. The transcriptional start site of fegA was mapped by primer extension analysis, and a putative Fur-binding site was found in the promoter. Primer extension and RNA slot blot analysis demonstrated that fegA was expressed only in cells grown under iron-limiting conditions. This is the first report of the cloning of a gene encoding a putative Fe(III)-siderophore receptor from nitrogen-fixing rhizobia.
authors.affiliation: Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA.
authors.forename: K
authors.initials: K
authors.lastname: LeVier
authors.forename: M L
authors.initials: ML
authors.lastname: Guerinot
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D003001:Cloning, Molecular; D003470:Culture Media; D004269:DNA, Bacterial; D005290:Ferric Compounds; D015964:Gene Expression Regulation, Bacterial; D006090:Gram-Negative Bacteria / Q000378:metabolism; D006877:Hydroxamic Acids; D007501:Iron / Q000493:pharmacokinetics*; D008969:Molecular Sequence Data; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism; D012230:Rhizobiaceae / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D017422:Sequence Analysis, DNA
chemical_list: D001425:Bacterial Outer Membrane Proteins; D003470:Culture Media; D004269:DNA, Bacterial; D005290:Ferric Compounds; D006877:Hydroxamic Acids; D011956:Receptors, Cell Surface; C074579:iron (III) hydroxamate; C035902:siderophore receptors; D007501:Iron