Potential and Whole-genome Sequence-based Mechanism of Elongated-prismatic Magnetite Magnetosome Formation in Acidithiobacillus Ferrooxidans BYM

A magnetosome-producing bacterium Acidithiobacillus ferrooxidans BYM (At. ferrooxidans BYM) was isolated and magnetically screened. The magnetosome yield from 0.5896 to 13.1291 mg/g was achieved under different aeration rates, ferrous sulfate, ammonium sulfate, and gluconic acid concentrations at 30 ℃. TEM observed 6–9 magnetosomes in size of 20–80 nm irregularly dispersed in a cell. STEM-EDXS and HRTEM-FFT implied that the elongated-prismatic magnetite magnetosomes with {110} crystal faces grown along the [111] direction. Whole-genome sequencing and annotation of BYM showed that 3.2 Mb chromosome and 47.11 kb plasmid coexisted, and 322 genes associated with iron metabolism were discovered. Ten genes shared high similarity with magnetosome genes were predicted, providing sufficient evidence for the magnetosome-producing potential of BYM. Accordingly, we first proposed a hypothetic model of magnetosome formation including vesicle formation, iron uptake and mineralization, and magnetite crystal maturation in At. ferrooxidans. These indicated that At. ferrooxidans BYM would be used as a commercial magnetosome-producing microorganism.

Maghemite in Brazilian Iron Ores: Quantification of the Magnetite-Maghemite Isomorphic Series by Χ-ray Diffraction and the Rietveld Method, and Confirmation by Independent Methods

Maghemite (γ-Fe2O3) is a mineral formed from magnetite oxidation at low temperatures, an intermediate metastable term of the magnetite to hematite oxidation and could be mixed with both. It has magnetic susceptibility similar to magnetite, crystal structure close to magnetite with which it forms a solid solution, while compositionally it equals hematite. Maghemite is thus easily misidentified as magnetite by Χ-ray diffraction and/or as hematite by spot chemical analysis in iron ore characterization routines. Nonstoichiometric magnetite could be quantified in samples of Brazilian soils and iron ores by the Rietveld method using a constrained refinement of the Χ-ray patterns. The results were confirmed by reflected light microscopy and Raman spectroscopy, thus qualitatively validating the method. Χ-ray diffraction with the refinement of the isomorphic substitution of Fe2+ by Fe3+ along the magnetite-maghemite solid solution could help to suitably characterize maghemite in iron ores, allowing for the evaluation of its ultimate influence on mineral processing, as its effect on surface and breakage properties.

Chromites in Ordinary chondrite fusion crusts

<p>We studied 5 fall Ordinary Chondrites of different groups (H4, H5, LL5, LL6, L3.6) and an Antarctic meteorite (H5), in order to investigate possible compositional differences between the chromites present in the bulk and the chromites formed within the fusion crust. We report here the composition of about 50 chromites measured within the bulk and 70 chromites found in the crust.</p> <p>Chromites found in the bulk are usually anhedral and relatively large in size (several tens of micrometers), whereas chromites formed within the crust are consistently smaller (few micrometers in size) and can display anhedral, or subhedral to euhedral habit.</p> <p>The Mg# and Al# determined for all the chromites found in the bulk show a fair agreement with data reported in the literature for chromite compositions in ordinary chondrites (Bunch et al., 1967; Ramdohr, 1967; Rubin, 2003; Wlotzka, 2005), which display a small scatter of the Al# (ca.0.13±0.025) and a large variation of the Mg# (from 0.05 to 0.30).</p> <p>When compared with the ones found in the bulk, chromites found within the fusion crusts generally exhibit similar values of the Al#; however, they display a much larger scatter of the Mg# and, usually, also larger average Mg# (up to 0.65) than their conterparts in the bulk.</p> <p>Chromite in the fusion crusts are often associated to magnetite dendrites made up by magnetite octahedral crystals 200-400 nanometers wide; occasionally, other spinel group minerals can be found, as magnesiochromites and magnesioferrites. In most of the samples studied, several chromite crystals are mantled by magnetite crystals, whereas no magnetite crystal has been found mantled by chromites. Textural data so far collected suggest a crystallization sequence in the fusion crust: Olivine, Chromite, Magnetite.</p> <p> </p> <p><strong>References:</strong></p> <p>Bunch T.E., Keil K. and Snetsinger K.G. (1967). Chromite composition in relation to chemistry and texture of ordinary chondrites. Geochimica et Cosmochimica Acta, <strong>31</strong>, 1569-1582.</p> <p>Ramdohr P. (1967). Chromite and chromite chondrules in meteorites-I. Geochimica et Cosmochimica Acta, <strong>31</strong>, 1961-1967.</p> <p>Rubin A.E. (2003). Chromite-Plagioclase assemblages as a new shock indicator; implications for the shock and thermal histories of ordinary chondrites. Geochimica et Cosmochimica Acta, <strong>67</strong>, 2695–2709.</p> <p>Wlotzka F. (2005) Cr spinel and chromite as petrogenetic indicators in ordinary chondrites: Equilibration temperatures of petrologic types 3.7 to 6. Meteoritics and Planetary Science, <strong>40</strong>, 1673-1702</p> <p> </p>

Application of ion-exchange resin beads to produce magnetic adsorbents

Heavy metal ions are among the most dangerous contaminants, which can cause serious health problems. In this work, ion-exchange resin beads were used as supports for magnetite (Fe3O4) synthesis to produce heavy metal adsorbents which can be easily separated by magnetic field. The first step of the magnetite preparation was the replacement of hydrogen ions with Fe2+ and Fe3+ ions on the sulfonic acid groups of the resin. In the second step, magnetite particle formation was induced by coprecipitating the iron ions with sodium hydroxide. The regeneration of the ion-exchange resin was also carried out by using sodium hydroxide. SEM images verified that relatively large magnetite crystal particles (diameter = 100–150 nm) were created. The ion-exchange effect of the prepared magnetic adsorbent was also confirmed by applying Cu2+, Ni2+, Pb2+ and Cd2+ ions in adsorption experiments.

Defining the hematite topotaxial crystal growth in magnetite–hematite phase transformation

Magnetite and hematite iron oxides are minerals of great economic and scientific importance. The oxidation of magnetite to hematite is characterized as a topotaxial reaction in which the crystallographic orientations of the hematite crystals are determined by the orientation of the magnetite crystals. Thus, the transformation between these minerals is described by specific orientation relationships, called topotaxial relationships. This study presents electron-backscatter diffraction analyses conducted on natural octahedral crystals of magnetite partially transformed into hematite. Inverse pole figure maps and pole figures were used to establish the topotaxial relationships between these phases. Transformation matrices were also applied to Euler angles to assess the diffraction patterns obtained and confirm the identified relationships. A new orientation condition resulting from the magnetite–hematite transformation was characterized, defined by the parallelism between the octahedral planes {111} of magnetite and rhombohedral planes \{10\bar {1}1\} of hematite. Moreover, there was a coincidence between one of the octahedral planes of magnetite and the basal {0001} plane of hematite, and between dodecahedral planes {110} of magnetite and prismatic planes \{11\bar {2}0\} of hematite. All these three orientation conditions are necessary and define a growth model for hematite crystals from a magnetite crystal. A new topotaxial relationship is also proposed: (111)Mag || (0001)Hem and (\bar {1}\bar {1}1)_{\rm Mag} || (10\bar {1}1)_{\rm Hem}.

Evolution of mineral composition of fluxed sinter from iron ore concentrate of the Kovdor deposit

Metallurgical conversion methods are still missing iron ore with heterogeneous structure magnetite of the Kovdor deposit. Sintering mechanism of Kovdor concentrate was investigated in the wide CaO/SiO2 basicity range of 1.2 – 3.0 for sintering process conditions. Main influence of magnetite crystal structure on the way of charge phase changing in sintering process is shown for the first time. As a result of sintering with the low basicity of 1.2 – 2.0 two phases sinter system was formed, containing magnetite and silicate bond of melilitic composition. The analysis has shown that melilitic bond is the straight analog of the basic and acid blast furnace slag. The difficult mineral composition, containing four phases, is formed with the high basicity of 2.0 – 3.0. Magnetite and bond of crystals of calciumalumosilicoferrite are the main minerals, which occupy almost the whole volume of the sinter. By composition and number of phases, magnetite-ferritic composition is two-phase sinter system. Development of appropriate sintering process regimes is required for each of the determined sinter systems.

Identification of Fe-Containing Phase in Oxidation Process of BOF Slag

In this paper, the Fe-containing phases in BOF slag were identified before and after oxidized with atmospheric air. XRD and SEM with EDS results showed that The element Fe existed in slag in the form of calcium ferrite, wustite solid solution and hematite. Mg solid solute in wustite. After oxidized, magnetite became the major mineral phase in slag and Mg + replace the Fe2+ of magnetite crystal to form spinel.

NMR studies of the interactions between AMB-1 Mms6 protein and magnetosome Fe3O4 nanoparticles

NMR studies demonstrate that, the C-terminal Mms6 undergo conformation change upon magnetosome Fe3O4 crystals binding. The N-terminal hydrophobic packing arranges the DEEVE motifs into a correct assembly and orientation for magnetite crystal recognition.

Comparative Subcellular Localization Analysis of Magnetosome Proteins Reveals a Unique Localization Behavior of Mms6 Protein onto Magnetite Crystals

ABSTRACTThe magnetosome is an organelle specialized for inorganic magnetite crystal synthesis in magnetotactic bacteria. The complex mechanism of magnetosome formation is regulated by magnetosome proteins in a stepwise manner. Protein localization is a key step for magnetosome development; however, a global study of magnetosome protein localization remains to be conducted. Here, we comparatively analyzed the subcellular localization of a series of green fluorescent protein (GFP)-tagged magnetosome proteins. The protein localizations were categorized into 5 groups (short-length linear, middle-length linear, long-length linear, cell membrane, and intracellular dispersing), which were related to the protein functions. Mms6, which regulates magnetite crystal growth, localized along magnetosome chain structures under magnetite-forming (microaerobic) conditions but was dispersed in the cell under nonforming (aerobic) conditions. Correlative fluorescence and electron microscopy analyses revealed that Mms6 preferentially localized to magnetosomes enclosing magnetite crystals. We suggest that a highly organized spatial regulation mechanism controls magnetosome protein localization during magnetosome formation in magnetotactic bacteria.IMPORTANCEMagnetotactic bacteria synthesize magnetite (Fe3O4) nanocrystals in a prokaryotic organelle called the magnetosome. This organelle is formed using various magnetosome proteins in multiple steps, including vesicle formation, magnetosome alignment, and magnetite crystal formation, to provide compartmentalized nanospaces for the regulation of iron concentrations and redox conditions, enabling the synthesis of a morphologically controlled magnetite crystal. Thus, to rationalize the complex organelle development, the localization of magnetosome proteins is considered to be highly regulated; however, the mechanisms remain largely unknown. Here, we performed comparative localization analysis of magnetosome proteins that revealed the presence of a spatial regulation mechanism within the linear structure of magnetosomes. This discovery provides evidence of a highly regulated protein localization mechanism for this bacterial organelle development.