The siderophore yersiniabactin binds copper to protect pathogens during infection.

Bacterial pathogens secrete chemically diverse iron chelators called siderophores, which may exert additional distinctive functions in vivo. Among these, uropathogenic Escherichia coli often coexpress the virulence-associated siderophore yersiniabactin (Ybt) with catecholate siderophores. Here we used a new MS screening approach to reveal that Ybt is also a physiologically favorable Cu(II) ligand. Direct MS detection of the resulting Cu(II)-Ybt complex in mice and humans with E. coli urinary tract infections demonstrates copper binding to be a physiologically relevant in vivo interaction during infection. Ybt expression corresponded to higher copper resistance among human urinary tract isolates, suggesting a protective role for this interaction. Chemical and genetic characterization showed that Ybt helps bacteria resist copper toxicity by sequestering host-derived Cu(II) and preventing its catechol-mediated reduction to Cu(I). Together, these studies reveal a new virulence-associated function for Ybt that is distinct from iron binding.