Characteristics of hollow microtubes consisting of amorphous iron oxide nanoparticles produced by iron oxidizing bacteria, Leptothrix ochracea

Some features of characteristic iron oxide sheaths which the iron oxidizing bacteria Leptothrix ochracea (L. oceracea) formed were studied in order to make clear their morphology microstructure, chemical composition, and crystal structure through scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD). Each sheath was a hollow tube with average outer and inner diameters of 1.1 and 1.4 μm, respectively. Their length ranged from 10 to 200 μm and the aspect ratio was 10-200. Each sheath was constructed by very small particles with a diameter of less than 100 nm. The hollow sheaths were mainly composed of Fe and O with small amounts of Si and P. The chemical composition analyzed by EDX was roughly Fe:Si:P=80:15:5 with the exception of O. XRD measurement revealed that crystal structures of the sheath were similar to that of 2-line ferrihydrite. The sheath showed spin-glass-like magnetic properties.