Enterochelin acquisition in Campylobacter coli: characterization of components of a binding-protein-dependent transport system.

Siderophore-mediated iron uptake systems play a central role in the pathogenesis of infection for many bacterial pathogens. Campylobacter species are not thought to produce siderophores, yet they are able to utilize both ferrichrome and enterochelin as sources of iron. Part of an operon named ceuBCDE, encoding components of a periplasmic binding-protein-dependent transport (PBT) system for the uptake of a ferric siderophore from Campylobacter coli, was cloned directly into Escherichia coli using a plasmid rescue technique. Phenotypic and genetic analyses of this system showed it to comprise two hydrophobic integral membrane proteins, CeuB (35.5 kDa) and CeuC (34.8 kDa), which may form the cytoplasmic membrane permease, an ATP-binding protein, CeuD (28.8 kDa), and a periplasmic substrate-binding protein, CeuE (34.5 kDa). In vivo labelling studies using [3H]palmitate demonstrated that CeuE, the periplasmic binding protein, is expressed as a lipoprotein in C. coli, which is unusual for a Gram-negative PBT system. Mutants of C. coli, defective in components of the transport mechanism, were severely impaired in the ability to utilize enterochelin as an iron source suggesting that this siderophore is a substrate for the transport system. This is the first molecular characterization of a PBT system in Campylobacter species.