Preparation and Characterization of Additional Metallic Element-Containing Tubular Iron Oxides of Bacterial Origin

Biogenic microtubular iron oxides (BIOXs) derived from Leptothrix spp. are known as promising multifunctional materials for industrial applications such as ceramic pigments and catalyst carriers. Here, we report unprecedented BIOX products with additive depositions of various metallic elements prepared by a newly devised "two-step" method using an artificial culture system of Leptothrix cholodnii strain OUMS1; the method comprises a biotic formation of immature organic sheaths and subsequent abiotic deposition of Fe and intended elements on the sheaths. Chemical composition ratios of the additional elements Al, Zr, and Ti in the respective BIOXs were arbitrarily controllable depending on initial concentrations of metallic salts added to reaction solutions. Raman spectroscopy exemplified an existence of Fe-O-Al linkage in the Al-containing BIOX matrices. Time-course analyses revealed the underlying physiological mechanism for the BIOX formation. These results indicate that our advanced method can contribute greatly to creations of innovative bioderived materials with improved functionalities.