Mössbauer spectroscopy and electron paramagnetic resonance studies of iron metabolites in Pseudomonas aeruginosa: Fe²⁺ and Fe³⁺ ferritin in⁵⁷ferripyoverdine incubated cells and⁵⁷ferric citrate fed cells

Pseudomonas aeruginosa samples were studied using Mössbauer spectroscopy and electron paramagnetic resonance (EPR). Samples included whole cells, membranes, and soluble fractions from cells which had been grown with⁵⁷ferric chloride,⁵⁷ferric citrate or incubated with⁵⁷ferripyoverdine. These experiments show for the first time that P. aeruginosa can accumulate iron in a bacterioferritin when grown under conditions of iron limitation and incubated with its cognate ferrisiderophore, ferripyoverdine. Soluble fraction from P. aeruginosa cells which were grown iron starved and incubated with⁵⁷ferripyoverdine for 120 min showed the presence of both a ferric and ferrous complex whose Mössbauer spectra matched that of bacterioferritin extracted from Azotobacter vinelandii and whose EPR spectra showed a characteristic ferritin-like resonance. A second soluble fraction sample from cells which had been grown with⁵⁷ferric citrate also showed the presence of a species with the same EPR and Mössbauer parameters. In addition Western blotting confirmed the presence of bacterioferritin in the soluble fraction of the cells which had been incubated with ferripyoverdine.