Time-resolved synchrotron X-ray powder diffraction study of biogenic nanomagnetite

The bacterium Geobacter sulfurreducens can produce nanoparticulate magnetite (Fe3O4) by the reduction of amorphous Fe(III) oxyhydroxide coupled to the oxidation of organic matter in the anoxic subsurface as an alternative to oxygen respiration. G. sulfurreducens can transfer electrons to solid Fe(III)-bearing minerals through either direct contact between the cell and the mineral surface or by using an electron shuttling compound. High resolution synchrotron X-ray powder diffraction has been used to study samples taken at different stages of this reaction. This shows that an initial amorphous phase first transforms to goethite (FeO(OH)), before undergoing a further transformation to magnetite. Magnetite is formed faster in the presence of the electron shuttling compound disodium anthraquinone 2,6 disulphonate.