Iron binding toAzotobacter salinestrismelanin, iron mobilization and uptake mediated by siderophores

✍ Scribed by William J. Page; Shailaja Shivprasad

• Book ID: 104646916
• Publisher: Springer Netherlands
• Year: 1995
• Tongue: English
• Weight: 418 KB
• Volume: 8
• Category: Article
• ISSN: 1572-8773
• DOI: 10.1007/bf00156159

✦ Synopsis

Iron-sufficient Azotobacter salinestris cells bound large amounts of SSFe to cell-associated catechol melanin in an energy-independent manner. Iron was mobilized from the cell surface by citric acid and transported into the cell in a process that was inhibited by azide, carbonyl cyanide m-chiorophenyl-hydrazone (CCCP), KCI or RbCl, the latter two known to inhibit Na+-dependent activities in A. salinestris. Iron-limited cells produced a hydroxamate compound (HDX) which promoted SSFe-uptake into iron-limited cells in a two step process. Initial uptake was inhibited by azide or CCCP, but not by KCI, while subsequent uptake was blocked by all inhibitors. Citric acid also mediated energy-dependent SSFe-uptake in iron-limited cells, but initial iron-uptake was less sensitive to CCCP than HDX-mediated iron-uptake. The results show that melanin serves as an iron trap, probably to protect the cells from oxidative damage mediated by H202 and the Fenton reaction. A model for HDX siderophore-mediated iron-uptake is proposed which requires energy to concentrate iron in the periplasm and H+/Na +-dependent events to bring iron into the cell.