Summary auto-generated
This study investigated the yellow-green fluorescent pigment (pyoverdine) produced by Pseudomonas fluorescens, focusing on its biosynthesis, purification, and chemical properties. Pyoverdine synthesis occurred exclusively under iron-deficient conditions and was independent of the carbon source used. The pigment formed a highly stable complex with Fe³⁺ ions, which facilitated purification. P. fluorescens produces only one molecular species of pyoverdine, though it degrades under mildly alkaline conditions to form multiple decomposition products. The purified pigment had a molecular weight of 1500±75 daltons and exhibited specific absorption and fluorescence spectra. The Fe³⁺-pigment complex was non-fluorescent and had a 1:1 stoichiometry. The stability constant for the Fe³⁺ complex was approximately 10³¹, comparable to other known siderophores. These properties—iron-dependent biosynthesis, strong Fe³⁺ chelation, and lack of affinity for Fe²⁺—suggested that pyoverdine functions as a siderophore in iron acquisition. This work resolved contradictory reports about pigment heterogeneity and clarified that apparent substrate-dependent pigmentation differences actually reflected varying iron requirements for growth on different carbon sources.
Key findings
- P. fluorescens produces pyoverdine exclusively under iron-deficient conditions; Fe³⁺ addition completely represses synthesis regardless of carbon source
- Pyoverdine forms a highly stable 1:1 Fe³⁺ complex with stability constant ~10³¹, comparable to known siderophores like ferroxamine B and ferrichrome
- The pigment is chemically labile under alkaline conditions, explaining previous observations of multiple pigment species as decomposition artifacts
- Apparent 'chromogenic' versus 'anti-chromogenic' substrate effects result from different specific iron requirements of the bacterium on various carbon sources, not from substrate-dependent pigment synthesis
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Abstract
The biosynthesis of a yellow-green, fluorescent, water-soluble pigment by Pseudomonas fluorescens occurred only when the bacteria were iron-deficient and was not directly influenced by the nature of the organic carbon source. The pigment formed a very stable Fe3+ complex and was purified in this form. Pseudomonas fluorescens produced only one molecular species of fluorescent pigment; however, its lability under mild alkaline conditions led to the formation of several pigmented decomposition products. The spectral properties of the pure pigment, its molecular weight (1500 ± 75) and its stability constant for Fe3+ (of the order of 1032) were determined. Both its biosynthesis and its chemical properties (formation of a stable Fe3+ complex) suggest that the fluorescent pigment is a desferrisiderophore.