SUMMARY: Azoverdin, a visible yellow, blue--white fluorescent compound produced by iron-limited ATCC 12334, was isolated from cell-free culture supernatant fluid and purified in the ferrated form to 98% purity by ion-exchange chromatography and reverse-phase high-performance liquid chromatography, thereby separating it from several related iron-binding fluorescent compounds. Purified ferrated azoverdin exhibited a pH-independent absorption spectrum which became pH-dependent following deferration, typical of a pyoverdin-like siderophore. Azoverdin enhanced Fe assimilation by iron-limited and therefore functioned as a siderophore. Iron-limited cells were unable to produce azoverdin when grown at 34 °C rather than 28 °C. However, these cells still expressed a 74 kDa and a 70 kDa iron-repressible outer membrane protein and were capable of azoverdin-mediated iron transport. The use of cells grown at 34 °C eliminated endogenous azoverdin production during iron uptake assays, which made it possible to accurately determine azoverdin-mediated Fe transport rates. Azoverdin-mediated Fe-uptake proceeded with an apparent of 0·2 μM and a of 0·46ng Fe (10 cells) min.


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