Pyoverdine-mediated regulation of FpvA synthesis in Pseudomonas aeruginosa: involvement of a probable extracytoplasmic-function sigma factor,FpvI

A search of the pvd pyoverdine biosynthesis locus of Pseudomonas aeruginosa identified an open reading frame, PA2387, whose product exhibited a sequence similar to those of a number of so-called extracytoplasmic- function sigma factors responsible for siderophore-dependent expression of iron-siderophore receptors in Escherichia coli and Pseudomonas putida. Deletion of this gene, dubbed fpvI, compromised pyoverdine-dependent FpvA ferric pyoverdine receptor production and fpvA gene expression, while the cloned gene stimulated fpvA expression. A Fur-binding site was identified immediately upstream of fpvI, consistent with the observed iron-regulated expression of fpvI and fpvA.