THE EFFECT OF MANGANESE OXIDES AND MANGANESE ION ON GROWTH AND SIDEROPHORE PRODUCTION BY AZOTOBACTER-VINELANDII

The addition of manganese oxides to iron-limited medium promoted the f ormation of the pyoverdin siderophore azotobactin by Azotobacter vinel andii. When active-MnO2 was used, there was greatly decreased iron upt ake into the cells, hyperproduction of azotobactin and the abiotic, ch emical destruction or adsorbtion of the catechol siderophores azotoche lin and aminochelin by this strong oxidizing agent. Although the iron content of the cells was the same as iron-limited cells, the growth of cells in medium with active-MnO2 was increased 1.5- to 2.5-fold over iron-limited controls. This growth promotion was not caused by iron co ntaminating the oxide or by manganese solubilized from the oxide. Solu ble 0.05-4 mM Mn2+ inhibited the growth of iron-limited cells and had a minimal effect on iron uptake, but caused hyperproduction of azotoba ctin. This later effect was caused by the inhibition of soluble ferric reductase, in a manner identical to that previously observed for Zn2. These results suggest that active-MnO2 may interfere with a surface- localized iron uptake site, possibly another ferric reductase. The rea son for the growth promotion by active-MnO2 remains unknown, but is mo st likely related to decreased oxygen toxicity.