Role of PyoverdinePf, the Iron-binding Fluorescent Pigment of Pseudomonas fluorescens, in Iron Transport

This study demonstrates that pyoverdine, a yellow-green fluorescent pigment produced by Pseudomonas fluorescens, functions as a siderophore facilitating iron transport into the bacterium. Using radioactive 59Fe3+ uptake experiments, researchers showed that iron transport is an active, energy-dependent process that is temperature-sensitive and inhibited by metabolic poisons. When purified pyoverdine was added to the external medium, iron uptake rates increased approximately twofold, with saturation occurring at pigment concentrations equimolar to total iron present. The pigment contains the unusual amino acid 6-N-hydroxyornithine, also found in other known siderophores. These findings establish pyoverdine as a typical microbial iron chelator with properties characteristic of siderophores: synthesis is induced only under iron-deficient conditions, it specifically complexes Fe3+ with high stability, and it enhances iron uptake. This work clarifies the previously unknown physiological function of the yellow-green fluorescent pigments produced by Pseudomonas species.

Key findings

• Iron transport by P. fluorescens is an active process requiring energy and temperature-dependent, inhibited by metabolic poisons like 2,4-dinitrophenol and sodium azide
• Purified pyoverdine increases iron uptake rates approximately twofold in a concentration-dependent manner, with rate saturation at equimolar concentrations to total iron
• Pyoverdine functions as a siderophore, containing 6-N-hydroxyornithine and specifically complexing Fe3+ to facilitate iron transport
• Pyoverdine synthesis is derepressed only under iron-deficient conditions, consistent with typical siderophore behavior