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 (Si-30 and -50 ppm). 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.
Highlights
Some bacteria serve as distinct nucleation sites for mineral authigenesis in situ [1]
When OUMS1 was cultured in Si-0, microtubular sheaths covered with fibers were formed (Figure 1a)
The high-angle annular dark field (HAADF)-scanning transmission electron microscopy (STEM) image of the same structure showed that the sheath looked hollow and had a
Summary
Some bacteria serve as distinct nucleation sites for mineral authigenesis in situ [1]. A restricted number of aquatic bacterial species, mainly those belonging to the genera Sphaerotilus and Leptothrix, form extracellular microtubular sheaths with an X-ray diffraction (XRD)-amorphous texture composed of organic bacterial secretions and aquatic inorganics such as Fe, silicon (Si), phosphorus (P), and often calcium (Ca). The mechanism of this type of sheath formation is closely associated with the capacity of these organisms to accumulate and oxidize Fe and Mn in aquatic environments [3,4]. Sawayama et al [8] who first isolated OUMS1 reported that this strain produced clusters of hollow microtubular sheaths on the iron plates when cultured in SIGP (Silicon-Iron-Glucose-Peptone) liquid medium (hereafter referred to as cultured sheaths)
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