Hydroxamate siderophores, cell growth and Fe(III) cycling in two anaerobiciron 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 wit hout, a Fe(III)(tris)acetohydroxamic acid complex as a source of Fe(III). T hese experiments were conducted with goethite [alpha-FeOOH] and amorphous i ron hydroxide [Fe(OH)(3)(s)] to determine whether hydroxamate ligands can s timulate cell growth by dissolving Fe(III) from the mineral surface. We fou nd that solids reduced the bacterial activity by lowering dissolved Fe(III) concentrations relative to solid-free medium. Acetohydroxamate did not sig nificantly enhance cell growth, possibly because the Fe(III) was too diffic ult to reduce when complexed in a trihydroxamate complex. The hydroxamate l igand 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 lig and, and there is evidence for an abiotic pathway for Fe(II) oxidation in t he media containing hydroxamate. Copyright (C) 1999 Elsevier Science Ltd.