Hydroxamate siderophores, cell growth and FE (III) cycling in two anaerobic iron oxide media containing Geobacter metallireducens
We test the hypothesis that a versatile strain of iron bacteria, Geobacter metallireducens, can metabolize Fe(III) when it is complexed to hydroxamate ligands. Pure cultures were grown under anaerobic conditions with, and without, a Fe(III)(tris)acetohydroxamic acid complex as a source of Fe(III). These experiments were conducted with goethite [α-FeOOH] and amorphous iron hydroxide [Fe(OH) 3(s)] to determine whether hydroxamate ligands can stimulate cell growth by dissolving Fe(III) from the mineral surface. We found that solids reduced the bacterial activity by lowering dissolved Fe(III) concentrations relative to solid-free medium. Acetohydroxamate did not significantly enhance cell growth, possibly because the Fe(III) was too difficult to reduce when complexed in a trihydroxamate complex. The hydroxamate ligand also had a dramatic effect on the cell morphology, such cell numbers could be used as a measure of microbial activity in solutions with this ligand, and there is evidence for an abiotic pathway for Fe(II) oxidation in the media containing hydroxamate.