Science 352, 1105–1109 (2016)

Pathogenic bacteria scavenge essential metal nutrients from their host organisms, often through the biosynthesis and excretion of metal-chelating siderophores followed by re-uptake of the metal–siderophore complexes. Ghssein et al. have elucidated the biosynthesis of staphylopine, a metallophore produced by Staphylococcus aureus, which is structurally similar to the metal chelator nicotianamine found in plants. Comparison of the wild-type strain to strains carrying mutations within the staphylopine biosynthetic gene cluster by liquid chromatography and mass spectrometry led to characterization of metal–staphylopine complexes and identification of three key enzymes that define its biosynthetic pathway. A histidine-specific racemase first converts l-His to d-His, and a nicotianamine synthase homolog catalyzes the addition to d-His of α-aminobutyric acid derived from SAM. An opine synthase homolog then catalyzes the NADPH-dependent condensation of this intermediate with pyruvate to yield staphylopine. Once secreted out of the cell through a dedicated exporter, staphylopine can bind copper, nickel, cobalt, zinc or iron; a transporter also encoded in the gene cluster is responsible for importing the resulting metal–staphylopine complex. As homologous gene clusters have also been identified in other pathogens, this enhanced understanding of bacterial metal acquisition could aid efforts to treat infections by these strains.