Silicon-Rich, Iron Oxide Microtubular Sheath Produced by an Iron-Oxidizing Bacterium, Leptothrix sp. Strain OUMS1, in Culture

Abstract

This study aimed to manipulate the texture and elemental composition of the novel sheaths produced by the iron-oxidizing bacterium Leptothrix in culture by altering components of the medium. When previously isolated strain OUMS1 was cultured in media (pH 7.0 throughout incubation) containing various levels of Si on a rotary shaker at 20 °C and 70 rpm for 14 days, the strain was able to reproduce in media with up to 300 ppm Si, and the hollow microtubular architecture of the sheath was maintained even at 300 ppm Si. The constitutional iron oxide phase changed from poorly crystalline lepidocrocite at 0 ppm Si to X-ray diffraction (XRD)-amorphous 2-line ferrihydrite at 100-300 ppm via their mixture phase with intermediate Si content . The results strongly indicate that the chemical character and crystallinity of the sheath texture can be regulated by culture conditions, especially components of the medium.

Use of Iron Powder to Obtain High Yields of Leptothrix Sheaths in Culture

“…Similar to the finding by Eggleton et al [22], a very broad peak at 30-40° and around 61° (black triangle in line A of Figure 4), plausibly was derived from two-line ferrihydrite (2Fh) [7], was observed for sheaths formed in the Fe plate medium. The sheaths that formed in the 0.14 g/L Fe powder medium showed a broad peak between 2θ = 15° and 31° (highest at 2θ = 20°), which was probably derived from C-containing constituents of bacterial and/or medium origin [23], and no remarkable peaks for the presence of Fe oxides were detected (line B of Figure 4).…”

“…As illustrated in Figure 3E,F, EDX analysis revealed a homogeneous distribution of Fe in a sheath that was harvested from the Fe powder medium. This distribution pattern was very similar to that in sheaths harvested from a two week culture of OUMS1 in the Fe plate medium as reported earlier [7,16]. The average atomic percentages of Fe in 10 spots of sheaths harvested after two weeks were 66.9 ± 9.9%, 82.4 ± 3.8%, and 88.9 ± 6.1% in 0.14, 1.4, and 14 g/L Fe powder medium, respectively, showing that Fe encrustation increased with increasing amount of Fe source in the medium.…”

“…Following the previous protocol [7], X-ray diffraction patterns of sheaths harvested from Fe powder and -plate media were obtained using an RINT-2000 (Rigaku, Tokyo, Japan) with Cu-Kα radiation (voltage, 40 kV; current, 200 mA). The dried specimens were pressed into an XRD holder with a glass plate to flatten the surface of the compacted powders.…”

“…The filamentous growth of Leptothrix species, the capability to form microtubular sheaths, and the precipitation of copious amounts of oxidized Fe or Mn distinguish the genus from other phylogenetically related genera [2,3]. To date, many researchers have reported that the major inorganic component of these sheaths is in the form of iron oxides that bind other inorganics such as Si, P, and often Ca and S [4][5][6][7][8]. Our previous microscopic and spectroscopic studies proved that the sheath was an ingenious hybrid of organic and inorganic materials produced through the interaction of bacterial exopolymers with aqueous-phase inorganics [5,8,9].…”

Direct Adherence of Fe(III) Particles onto Sheaths of Leptothrix sp. Strain OUMS1 in Culture

“…Our previous study further indicated that the chemical character and crystallinity of the sheath matrix can be modified depending on the culture conditions for the strains, especially on the components of the medium [30]. These findings encouraged us to elucidate the encrustation mechanism of sheaths in culture in more detail so that we can rationally manipulate the matrix and elemental composition of Leptothrix sheaths to further increase the usefulness of the material and to create novel functional materials.…”