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Structural purity of magnetite nanoparticles in magnetotactic bacteria.

Fischer A, Schmitz M, Aichmayer B, Fratzl P, Faivre D - J R Soc Interface (2011)

Bottom Line: However, even if the magnetosome chains are well characterized, controversial results about the microstructure of magnetosomes were obtained and its possible influence in the formation of the magnetic dipole is to be specified.Significant differences in the lattice parameter were found between intracellular magnetosomes from cultured magnetotactic bacteria and isolated ones.Through comparison with abiotic control materials of similar size, we show that this difference can be associated with different oxidation states and that the biogenic nanomagnetite is stoichiometric, i.e. structurally pure whereas isolated magnetosomes are slightly oxidized.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, , Science Park Golm, 14424 Potsdam, Germany.

ABSTRACT
Magnetosome biomineralization and chain formation in magnetotactic bacteria are two processes that are highly controlled at the cellular level in order to form cellular magnetic dipoles. However, even if the magnetosome chains are well characterized, controversial results about the microstructure of magnetosomes were obtained and its possible influence in the formation of the magnetic dipole is to be specified. For the first time, the microstructure of intracellular magnetosomes was investigated using high-resolution synchrotron X-ray diffraction. Significant differences in the lattice parameter were found between intracellular magnetosomes from cultured magnetotactic bacteria and isolated ones. Through comparison with abiotic control materials of similar size, we show that this difference can be associated with different oxidation states and that the biogenic nanomagnetite is stoichiometric, i.e. structurally pure whereas isolated magnetosomes are slightly oxidized. The hierarchical structuring of the magnetosome chain thus starts with the formation of structurally pure magnetite nanoparticles that in turn might influence the magnetic property of the magnetosome chains.

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(a) The lattice parameters measured for the samples are reported (same colours and samples as in figure 2). In (b) the oxidation parameter z of each sample can be determined based on the fit a(z) = 8.3956 − 0.0224z + 0.0026z2 − 0.0273z3, R2 = 0.990) of the experimental data of Dunlop & Özdemir [37]. Focusing on the biogenic (z = 0.00) and abiotic (z = 0.21) MGT samples, the saturation moment Ms can be seen in (c) based on their oxidation parameter and on the fit Ms (z) = 4.0285 − 0.6983z − 0.3961z2, R2 = 0.998) of the experimental data of Dunlop & Özdemir [37]. The biogenic magnetite samples thereby exhibit Ms = 4.03 µB whereas the abiotic has a calculated saturation moment of 3.86 µB.
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RSIF20100576F4: (a) The lattice parameters measured for the samples are reported (same colours and samples as in figure 2). In (b) the oxidation parameter z of each sample can be determined based on the fit a(z) = 8.3956 − 0.0224z + 0.0026z2 − 0.0273z3, R2 = 0.990) of the experimental data of Dunlop & Özdemir [37]. Focusing on the biogenic (z = 0.00) and abiotic (z = 0.21) MGT samples, the saturation moment Ms can be seen in (c) based on their oxidation parameter and on the fit Ms (z) = 4.0285 − 0.6983z − 0.3961z2, R2 = 0.998) of the experimental data of Dunlop & Özdemir [37]. The biogenic magnetite samples thereby exhibit Ms = 4.03 µB whereas the abiotic has a calculated saturation moment of 3.86 µB.

Mentions: While the inverse spinel structure and the face-centred cubic unit cell are conserved, maghemitization results in a lattice parameter decrease [37]. This reduction is induced by the creation of vacancies in the iron lattice and the change in Goldschmidt radius from 0.83 to 0.67 Å, as Fe(II) is oxidized to Fe(III) [37]. The lattice parameter of the bacterial magnetite fits perfectly with stoichiometric magnetite [32], whereas that of the reference sample reveals slight oxidation (figure 4). This result is not surprising since Fe(II) can easily be oxidized to Fe(III) under environmental conditions. With a lattice parameter of aa MGT = 8.3907 Å, and a third-order polynomial (best) fit of the literature experimental a(z) plot [37] (figure 3), an oxidation state of z = 0.21 can be estimated for the reference abiotic magnetite that in our opinion depicted the equilibrium state of magnetite nanoparticles under atmospheric conditions.Figure 4.


Structural purity of magnetite nanoparticles in magnetotactic bacteria.

Fischer A, Schmitz M, Aichmayer B, Fratzl P, Faivre D - J R Soc Interface (2011)

(a) The lattice parameters measured for the samples are reported (same colours and samples as in figure 2). In (b) the oxidation parameter z of each sample can be determined based on the fit a(z) = 8.3956 − 0.0224z + 0.0026z2 − 0.0273z3, R2 = 0.990) of the experimental data of Dunlop & Özdemir [37]. Focusing on the biogenic (z = 0.00) and abiotic (z = 0.21) MGT samples, the saturation moment Ms can be seen in (c) based on their oxidation parameter and on the fit Ms (z) = 4.0285 − 0.6983z − 0.3961z2, R2 = 0.998) of the experimental data of Dunlop & Özdemir [37]. The biogenic magnetite samples thereby exhibit Ms = 4.03 µB whereas the abiotic has a calculated saturation moment of 3.86 µB.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3104334&req=5

RSIF20100576F4: (a) The lattice parameters measured for the samples are reported (same colours and samples as in figure 2). In (b) the oxidation parameter z of each sample can be determined based on the fit a(z) = 8.3956 − 0.0224z + 0.0026z2 − 0.0273z3, R2 = 0.990) of the experimental data of Dunlop & Özdemir [37]. Focusing on the biogenic (z = 0.00) and abiotic (z = 0.21) MGT samples, the saturation moment Ms can be seen in (c) based on their oxidation parameter and on the fit Ms (z) = 4.0285 − 0.6983z − 0.3961z2, R2 = 0.998) of the experimental data of Dunlop & Özdemir [37]. The biogenic magnetite samples thereby exhibit Ms = 4.03 µB whereas the abiotic has a calculated saturation moment of 3.86 µB.
Mentions: While the inverse spinel structure and the face-centred cubic unit cell are conserved, maghemitization results in a lattice parameter decrease [37]. This reduction is induced by the creation of vacancies in the iron lattice and the change in Goldschmidt radius from 0.83 to 0.67 Å, as Fe(II) is oxidized to Fe(III) [37]. The lattice parameter of the bacterial magnetite fits perfectly with stoichiometric magnetite [32], whereas that of the reference sample reveals slight oxidation (figure 4). This result is not surprising since Fe(II) can easily be oxidized to Fe(III) under environmental conditions. With a lattice parameter of aa MGT = 8.3907 Å, and a third-order polynomial (best) fit of the literature experimental a(z) plot [37] (figure 3), an oxidation state of z = 0.21 can be estimated for the reference abiotic magnetite that in our opinion depicted the equilibrium state of magnetite nanoparticles under atmospheric conditions.Figure 4.

Bottom Line: However, even if the magnetosome chains are well characterized, controversial results about the microstructure of magnetosomes were obtained and its possible influence in the formation of the magnetic dipole is to be specified.Significant differences in the lattice parameter were found between intracellular magnetosomes from cultured magnetotactic bacteria and isolated ones.Through comparison with abiotic control materials of similar size, we show that this difference can be associated with different oxidation states and that the biogenic nanomagnetite is stoichiometric, i.e. structurally pure whereas isolated magnetosomes are slightly oxidized.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, , Science Park Golm, 14424 Potsdam, Germany.

ABSTRACT
Magnetosome biomineralization and chain formation in magnetotactic bacteria are two processes that are highly controlled at the cellular level in order to form cellular magnetic dipoles. However, even if the magnetosome chains are well characterized, controversial results about the microstructure of magnetosomes were obtained and its possible influence in the formation of the magnetic dipole is to be specified. For the first time, the microstructure of intracellular magnetosomes was investigated using high-resolution synchrotron X-ray diffraction. Significant differences in the lattice parameter were found between intracellular magnetosomes from cultured magnetotactic bacteria and isolated ones. Through comparison with abiotic control materials of similar size, we show that this difference can be associated with different oxidation states and that the biogenic nanomagnetite is stoichiometric, i.e. structurally pure whereas isolated magnetosomes are slightly oxidized. The hierarchical structuring of the magnetosome chain thus starts with the formation of structurally pure magnetite nanoparticles that in turn might influence the magnetic property of the magnetosome chains.

Show MeSH