Siderophore specificities of the Pseudomonas aeruginosa TonB‐dependent transporters ChtA and ActA

Iron is an essential nutrient for the survival and virulence of Pseudomonas aeruginosa. The pathogen expresses at least 15 different iron‐uptake pathways, the majority involving small iron chelators called siderophores. P. aeruginosa produces two siderophores, but can also use many produced by other microorganisms. This implies that the bacterium expresses appropriate TonB‐dependent transporters (TBDTs) at the outer membrane to import the ferric form of each of the siderophores used. Here, we show that the two α‐carboxylate‐type siderophores rhizoferrin‐Fe and staphyloferrin A‐Fe are transported into P. aeruginosa cells by the TBDT ActA. Among the mixed α‐carboxylate/hydroxamate‐type siderophores, we found aerobactin‐Fe to be transported by ChtA and schizokinen‐Fe and arthrobactin‐Fe by ChtA and another unidentified TBDT. Our findings enhance the understanding of the adaptability of P. aeruginosa and hold significant implications for developing novel strategies to combat antibiotic resistance.