Characterization of microtubule material consisting of iron oxide nanoparticles produced by bacteria

Iron oxide microtubules produced by a species of iron-oxidizing bacteria, Leptothrix ochracea, have been expected to be useed as unique multifunctional materials such as catalysts scaffolds, pigments, and magnetic materials. However, their structural characteristics and formation mechanism are still ambiguous. The detailed features of the microtubules were characterized through electron microscopies, X-ray diffractometory, and energy dispersive X-ray spectroscopy. We found that the microtubules have hierarchical microstructures with aggregates of amorphous iron oxide nanoparticles. Statistical analysis of distributions of the tubule diameters and the wall thicknesses suggested that the tubule layer could grow from outside to inside.