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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.

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Mössbauer spectroscopy was used to investigate the cellular acquisition of iron by Pseudomonas aeruginosa which had been incubated with ferripyoverdine for 20, 40, 60, 120 or 360 min. Studies revealed that no ferripyoverdine accumulated in the cells at any of these times and that the amounts and kinds of iron complexes produced by cellular metabolism vary with time. At 20 and 40 min a ferric species, with isomer shift delta = 0.38-0.42 mm/s and quadrupole splitting delta EQ = 0.94-0.92 mm/s, was the major iron metabolite comprising approximately 80% of the iron. At later times at least three other ferric species appeared with delta = 0.54----0.72, delta EQ = 0.84----1.07 mm/s. Ferrous species, delta = 1.43----1.77 mm/s and delta EQ = 2.69----1.82 mm/s, were also seen at times as early as 20 min and comprised as much as 17% of the total iron at 20 and 40 min. The parameters of all these species identify them as being six-coordinated high-spin complexes. In addition a low-spin species, delta = 0.19 mm/s delta EQ = 0.67----0.91 mm/s, never before reported in cells, appeared at 60, 120, and 360 min as one of the major iron metabolites (50% or more). All isomer shifts are measured with respect to natural iron.

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