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Two ferric ion-binding compounds, designated staphyloferrin A and B, were detected in the culture filtrates of staphylococci-grown under iron-deficient conditions. Staphyloferrin A was isolated from cultures of Staphylococcus hyicus DSM 20459. The structural elucidation of this highly hydrophilic, acid-labile compound revealed a novel siderophore, N2,N5-di-(l-oxo-3-hydroxy-3,4-dicarboxybutyl)-D-ornithine, which consists of one ornithine and two citric acid residues linked by two amide bonds. The two citric acid components of staphyloferrin A provide two tridentate pendant ligands, comprising of a β-hydroxy, β-carboxy-substituted carboxylic acid derivative, for octahedral metal chelation. The CD spectrum of the staphyloferrin A ferric complex indicates a predominant A configuration about the ferric ion center. The uptake of ferric staphyloferrin A by S. hyicus obeys Michaelis-Menten kinetics (Km= 0.246 μM; vmax= 82 pmol · mg−1· min−1), indicating active transport of this siderophore. The staphyloferrin A transport system is different from that of the ferrioxamines as shown by an antagonism test. Production of staphyloferrin A is strongly iron-dependent and is stimulated by supplementation of the medium with either D- or L-ornithine. DL-[5-14C]ornithine was incorporated into staphyloferrin A, demonstrating that ornithine is an intermediate in staphyloferrin A biosynthesis.