TEMPERATURE-SENSITIVE PRODUCTION OF AZOVERDIN, THE PYOVERDIN-LIKE SIDEROPHORE OF AZOMONAS-MACROCYTOGENES ATCC-12334

Azoverdin, a visible yellow, blue-white fluorescent compound produced by iron-limited Azomonas macrocytogenes 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 the pyoverdin-like siderophore. Azoverdin enhanced 55Fe3+ assimsilation by iron-limited A. macrocytogenes and therefore functioned as a siderophore. Iron-limited cells were unable to produce azoverdin when growtn 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 A. macrocytogenes cells grown at 34°C eliminated endogenous azoverdin production during iron uptake assays, which made it possible to accurately determine azoverdin-mediated 55Fe3+ transport rates. Azoverdin-mediated 55Fe-uptake proceeded with an apparent K(m) of 0.2 μM and a V of 0.46 ng Fe3+ (108 cells)-1 min-1.