Fluorescence of Pyoverdin in Response to Iron and Other Common Well Water Metals

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⁺.

Key Words:

• Pyoverdin
• Fluorescence
• Iron
• Metal
• Well water
• 96-well plate.

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.