The availability of iron from various solid-phase iron sources to a siderophore producing Pseudomonas strain

Non-crystalline or short-range order Fe oxides (sometimes called amorphous Fe oxides) are of interest because of their surface area and high reactivity, and their influence on Fe availability in the soil. Eight non-crystalline Fe(III) oxides were precipitated from solutions with Si/Fe(III) molar ratios ranging from 0.00 to 1.00. These eight Fe oxides, along with goethite and hematite, were evaluated for their ability to supply Fe to an isolate of Pseudomonas obtained from grass roots. Levels of siderophore in solution were significantly higher in controls (with no Fe added) and in the presence of hematite or the more-crystalline goethite sample, than with the non-crystalline oxide treatments. The non-crystalline oxides were indistinguishable in their ability to suppress siderophore production. Greater numbers of Pseudomonas were observed in cultures amended with the non-crystalline oxides than in the cultures amended with crystalline oxides or in the Fe-deficient controls.