A Mössbauer spectroscopy study of cellular acquisition of iron from pyoverdine by Pseudomonas aeruginosa

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.