Pyoverdine-mediated iron transport. Fate of iron and ligand in Pseudomonas aeruginosa.

Incubated in the presence of [55Fe]ferri[14C]pyoverdine, iron-poor Pseudomonas aeruginosa accumulated more 55Fe than 14C over a 60-min period. Distribution studies showed (a) more 14C than 55Fe in the soluble fraction during the first 20 min, (b) approximately 60% of the 55Fe associated with the membranes at 60 min, and (c) approximately 85% of the 14C in the soluble fraction at 60 min. Cells osmotically shocked after incubating with [55Fe]ferri[14C]pyoverdine for 60 min released 55Fe but not 14C, suggesting separation of metal and ligand in the periplasmic space. Whereas the mechanism of dissociation of iron and ligand is not known, the decrease in transport observed in the presence of dipyridyl suggests involvement of reduction in this process. Transport of iron was energized by the proton motive force instead of by intracellular levels of ATP. The hydrogen ion gradient was the major driving force of transport. Cyanide-poisoned cells accumulated more 14C than 55Fe over 60 min. Here, iron accumulated in the soluble fraction instead of on the membranes.