Fe3O4 precipitation in magnetotactic bacteria

Using Mössbauer resonance spectroscopy of ⁵⁷Fe, we have determined the nature and distribution of major iron compounds in the magnetotactic bacterium Aquaspirillum magnetotacticum. In addition to magnetite (Fe₃O₄), cells contained a low-density hydrous ferric oxide, a high-density hydrous ferric oxide (ferrihydrite), and ferrous iron. Analysis at different temperatures of whole cells harvested early and late in growth, of mutant cells unable to synthesize magnetite, and of cell fractions enriched in ⁵⁷Fe indicated that Fe₃O₄ precipitation resulted from partial reduction of the high-density hydrous ferric oxide precursor.