Leptothrix sp. sheaths modified with iron oxide particles: Magnetically responsive, high aspect ratio functional material.

Smart materials of biological origin are attracting a lot of attention nowadays, especially as catalysts, carriers or adsorbents. Among them, magnetically modified biomaterials are especially important due to their response to external magnetic field. This report demonstrates that naturally occurring micrometer sized, high aspect ratio material (native and autoclaved Leptothrix sp. sheaths) efficiently bind synthetically prepared magnetite and maghemite nanoparticles and their aggregates. Magnetic modification of Leptothrix sheaths enables to prepare a promising material for advanced biotechnology and environmental technology applications. The prepared magnetically responsive sheaths were tested as inexpensive adsorbent for crystal violet removal from aqueous solutions. The observed maximum adsorption capacity was 243.1mg of dye per 1g of adsorbent.

Investigation of iron-containing products from natural and laboratory cultivated Sphaerotilus-Leptothrix bacteria.

Bacterial biomass collected from sheath-forming bacteria of the genera Sphaerotilus and Leptothrix was collected from a high-mountain natural stream water source. The elemental constitution and oxide phases of the products after selective cultivation of the bacteria on two different elective media using neutron activation analysis (NAA), electron microscopy (SEM, TEM), and X-ray diffraction (XRD) were studied. A high enrichment level of iron was revealed by the NAA technique in cultivated isolates as compared to the reference sample from nature. Three types of iron oxide compounds were established after cultivation in Adler's medium: lepidocrocite (γ-FeOOH), magnetite (Fe3O4), and goethite (α-FeOOH). The cultivation in the Isolation medium yielded a single phase, that of goethite, excluding one sample with a distinguishable amount of lepidocrocite. XRD and EM investigations show that the biogenic oxides are nanosized. Our study exemplifies the possibilities of the biotechnology approach for obtaining, under artificial conditions, large quantities of iron-containing by-products that could be of further used in appropriate nano- and biotechnologies.

Bacterial nanometric amorphous Fe-based oxide: a potential lithium-ion battery anode material.

Amorphous Fe(3+)-based oxide nanoparticles produced by Leptothrix ochracea, aquatic bacteria living worldwide, show a potential as an Fe(3+)/Fe(0) conversion anode material for lithium-ion batteries. The presence of minor components, Si and P, in the original nanoparticles leads to a specific electrode architecture with Fe-based electrochemical centers embedded in a Si, P-based amorphous matrix.

Nano-micrometer-architectural acidic silica prepared from iron oxide of Leptothrix ochracea origin.

We prepared nano-micrometer-architectural acidic silica from a natural amorphous iron oxide with structural silicon which is a product of the iron-oxidizing bacterium Leptothrix ochracea. The starting material was heat-treated at 500 °C in a H2 gas flow leading to segregation of α-Fe crystalline particles and then dissolved in 1 M hydrochloric acid to remove the α-Fe particles, giving a gray-colored precipitate. It was determined to be amorphous silica containing some amount of iron (Si/Fe = ~60). The amorphous silica maintains the nano-microstructure of the starting material-~1-µm-diameter micrometer-tubules consisting of inner globular and outer fibrillar structures several tens of nanometer in size-and has many large pores which are most probably formed as a result of segregation of the α-Fe particles on the micrometer-tubule wall. The smallest particle size of the amorphous silica is ~10 nm, and it has a large surface area of 550 m(2)/g with micropores (0.7 nm). By using pyridine vapor as a probe molecule to evaluate the active sites in the amorphous silica, we found that it has relatively strong Brønsted and Lewis acidic centers that do not desorb pyridine, even upon evacuation at 400 °C. The acidity of this new silica material was confirmed through representative two catalytic reactions: ring-opening reaction and Friedel-Crafts-type reaction, both of which are known to require acid catalysts.

Structural and spatial associations between Fe, O, and C in the network structure of the Leptothrix ochracea sheath surface.

The structural and spatial associations of Fe with O and C in the outer coat fibers of the Leptothrix ochracea sheath were shown to be substantially similar to the stalk fibers of Gallionella ferruginea, i.e., a central C core, probably of bacterial origin, and aquatic Fe interacting with O at the surface of the core.

Chemical modification of biogenous iron oxide to create an excellent enzyme scaffold.

The biogenous iron oxide (BIO) from Leptothrix ochracea was transformed to an organic-inorganic hybrid support to prepare an excellent immobilized enzyme showing high catalytic performance.

Solubilization and structural determination of a glycoconjugate which is assembled into the sheath of Leptothrix cholodnii.

The sheath of Leptothrix cholodnii is constructed from a structural glycoconjugate, a straight-chained amphoteric heteropolysaccharide modified with glycine and cysteine. Though the structure of the glycan core is already determined, its modifications with amino acids and other molecules are not fully resolved. In this study, we aimed to determine the chemical structure of the glycoconjugate as a whole. Enantiomeric determination of cysteine in the sheath was performed and as a result, L-cysteine was detected. NMR spectroscopy was endeavored to determine overall structure of the glycoconjugate. Prior to NMR analysis, solubilization of the glycoconjugate was attempted by adding denaturing reagents or by derivatization. As far as tested, sulfonation by performic acid oxidation was suitable for solubilization, but further improvement was achieved by N-acetylation. The approximate molecular weight of the derivative was estimated to be 4.5 x 10(4) by size-exclusion chromatography. The NMR studies for the sulfonated glycoconjugate and its N-acetylated derivative revealed that the sheath glycoconjugate is a glycosaminoglycan consisting of a pentasaccharide repeating unit which is substoichiometrically esterified with 3-hydroxypropionic acid and stoichiometrically amidated with acetic acid and glycyl-L-cysteine.

Zn sorption mechanisms onto sheathed Leptothrix discophora and the impact of the nanoparticulate biogenic Mn oxide coating.

Zinc sorption on sheathed Leptothrix discophora bacterium, the isolated extracellular polymeric substances (EPS) sheath, and Mn oxide-coated bacteria was investigated with macroscopic and spectroscopic techniques. Complexation with L. discophora was dominated by the outer membrane phosphoryl groups of the phospholipid bilayer while sorption to isolated EPS was dominated by carboxyl groups. Precipitation of nanoparticulate Mn oxide coatings on the cell surface increased site capacity by over twenty times with significant increase in metal sorption. XAS analysis of Zn sorption in the coated system showed Mn oxide phase contributions of 18 to 43% through mononuclear inner-sphere complexes. The coordination environments in coprecipitation samples were identical to those of sorption samples, indicating that, even in coprecipitation, Zn is not incorporated into the Mn oxide structure. Rather, through enzymatic oxidation by L. discophora, Mn(II) is oxidized and precipitated onto the biofilm providing a large surface for metal sequestration. The nanoparticulate Mn oxide coating exhibited significant microporosity (75%) suggesting contributions from intraparticle diffusion. Transient studies conducted over 7 months revealed a 170% increase in Zn loading. However, the intraparticle diffusivity of 10(-19) cm(2) s(-1) is two orders of magnitude smaller than that for abiotic Mn oxide which we attribute to morphological changes such as reduced pore sizes in the nanoparticulate oxide. Our results demonstrate that the cell-bound Mn oxide particles can sorb significant amounts of Zn over long periods of time representing an important surface for sequestration of metal contaminants.

Atomic-scale structure of biogenic materials by total X-ray diffraction: a study of bacterial and fungal MnOx.

Biogenic materials are produced by microorganisms and are typically found in a nanophase state. As such, they are difficult to characterize structurally. In this report, we demonstrate how high-energy X-ray diffraction and atomic pair distribution function analysis can be used to determine the atomic-scale structures of MnO(x) produced by bacteria and fungi. These structures are well-defined, periodic, and species-specific, built of Mn-O(6) octahedra forming birnessite-type layers and todorokite-type tunnels, respectively. The inherent structural diversity of biogenic material may offer opportunities for practical applications.

Identification of 2-(cysteinyl)amido-2-deoxy-D-galacturonic acid residue from the sheath of Leptothrix cholodnii.

The sheath of Leptothrix cholodnii is a glycoconjugate composed of a polysaccharide and a peptide rich in cysteine. In this study, structural determination of the hydrazinolyzate of the sheath was carried out. Since the hydrazinolyzate is a polysaccharide incorporated with cysteine, it was S-derivatized with a thiol-specific fluorogenic reagent, 4-(aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (ABD-F). Fluorescent fragments were purified by HPLC, and their structures were analyzed by mass spectrometry and NMR spectroscopy. The sheath was found to contain 2-(cysteinyl)amido-2-deoxy-D-galacturonic acid residue.

Laboratory modelling of manganese biofiltration using biofilms of Leptothrix discophora.

Laboratory biofilters (pilot-scale, 20 l and laboratory-scale, 5l) were constructed in order to model the bioaccumulation of manganese (Mn) under flow conditions similar to those occurring in biofilters at groundwater treatment sites. The biofilters were operated as monocultures of Leptothrix discophora, the predominant organism in mature Mn oxidising biofilms. Biologically mediated Mn bioaccumulation was successfully modelled in both filter systems. The data obtained showed that in the small-scale biofilter, the Mn concentrations that gave the highest rate of Mn bioaccumulation, shortest maturation time, highest optical density (biomass) and growth rate were between 2000 and 3000 microg x l(-1). The non-problematic scale-up of the process from the laboratory-scale to the pilot-scale biofilter model suggests that Mn biofilters may be 'seeded' with laboratory grown cultures of L. discophora. By initially operating the biofilter as a re-circulating batch culture, with an initial Mn concentration of approximately 2500 microg x l(-1), it is hoped to reduce the filter maturation time from months to days.

Biological treatment of Mn(II) and Fe(II) containing groundwater: kinetic considerations and product characterization.

In the present article, the treatment of groundwater containing Mn(II) and Fe(II) has been investigated. The biological oxidation of Mn(II) and Fe(II) in upflow filtration units comprised the applied experimental technique. The oxidation processes were mediated by specific bacteria, namely the Leptothrix ochracea and Gallionella ferruginea, which belong to the general category of manganese and iron oxidizing bacteria. This work was focused on the characterization of the products of biological oxidation and to the examination of the kinetics of Mn(II) removal as compared with Fe(II) removal from groundwaters. The products of biological oxidation were characterized using the spectroscopic techniques XRD, XPS and SEM-EDS and comprised a mixture of biogenic hydrous manganese and iron oxides. The oxidation state of manganese in the precipitates was found to be between 3 and 4. Iron oxides were mainly in the form of amorphous ferrihydrite. The kinetic results indicated that the rates of manganese and iron oxidation were several orders of magnitude greater than the respective for abiotic oxidation. The bacterially mediated oxidation of iron was faster than manganese oxidation, presenting half-lives of reaction 0.9 and 3.98 min, respectively.