Characterization of a pyoverdine-deficient mutant of Pseudomonas fluorescens impaired in the secretion of extracellular lipase.

A mutant of Pseudomonas fluorescens strain B52 deficient in the synthesis of the fluorescent pigment, pyoverdine, was isolated. Absence of pyoverdine and other siderophores was confirmed by gel filtration, a specific siderophore assay, and inhibition studies with the iron chelator EDDA. Both parent and mutant synthesized additional outer membrane proteins in response to iron-limitation. Mutant cells cultured in the absence of iron(III) accumulated 55Fe-labeled pyoverdine. The mutant produced extracellular proteinase normally on various media, but was deficient in lipase secretion. Growth of the mutant with partially-purified pyoverdine resulted in a 2.5-fold stimulation of lipase secretion. The mutant grew poorly in deferrated medium; however, the addition of iron(III) stimulated growth. Proteinase secretion in deferrated medium was stimulated over a narrow range of iron(III) concentration, while lipase secretion was only slightly affected. The data suggest that separate regulatory mechanisms exist for the control of proteinase and lipase secretion by iron(III).