When the fluorescent siderophore pyoverdin (produced by Pseudomonas aeruginosa) binds to a metal ion the fluorescence changes. A pyoverdin solution (in 0.1 M acetate buffer, pH 5.0) was placed in the microwells of a 96-well plate and varying concentrations of the metal cations Al3+, Ca2+, Cu2+, Fe2+, Fe3+, Mn2+, Mg2+, and Zn2+ were added. The fluorescence of pyoverdin 60 sec after the addition of an equimolar concentration of metal indicated: (1) no change for Ca2+, Fe2+, Mn2+, Mg2+, and Zn2+; (2) a small increase (109%) for Al3+; (3) decreases in fluorescence for Cu2+ (83%) and for Fe3+ (66%). The fluorescence of pyoverdin 24 hr after the addition of equimolar metal indicated: 1) very little change for Ca2+, Mn2+, Mg2+, and Zn2+; 2) a very large (270%) increase in fluorescence due to Al3+; 3) an increase (113%) due to Cu2+; 4) large decreases in fluorescence for both Fe2+ (15%) and Fe3+ (0%). Thus, for an iron assay using a free solution of pyoverdin, even with a short (60 sec.) reaction time there can be interference due to Cu2+, and interference due to high levels of Al3+.
ACKNOWLEDGMENTS
The authors thank Jeannie (Regina D.) Dawson, former Program Coordinator of the Soil, Plant, and Water Analysis Laboratory, (SPW), College of Environmental and Agricultural Sciences, UGA, for Georgia well water samples and data.