Multiple outer membrane receptors for uptake of ferric pseudobactins in Pseudomonas putida WCS358.

Under iron limitation Pseudomonas putida WCS358 produces a fluorescent siderophore, pseudobactin 358, which, after complexing iron, is transported back into the cell via the specific outer membrane receptor PupA. In addition, this strain has the capacity to take up iron via a large variety of siderophores produced by other fluorescent pseudomonads. Putative receptor genes for such siderophores were identified in the chromosome of strain WCS358 by PCR using primers matching two domains conserved in four ferric pseudobactin receptors, including PupA. Eleven amplification products within the expected size range were obtained. Sequence analysis confirmed that the products were derived from genes encoding outer membrane receptors. Two complete receptor genes were isolated from a genomic library of P. putida WCS358. Both protein products are involved in the transport of a limited number of specific ferric pseudobactins. These results indicate that the ability of P. putida WCS358 to exploit many different heterologous pseudobactins is related to the presence of multiple outer membrane receptor proteins.