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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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Calculated lattice parameters with standard deviations for biotic and abiotic samples for different magnetite and maghemite diffraction peaks. Same colours and samples as in figure 2.
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RSIF20100576F3: Calculated lattice parameters with standard deviations for biotic and abiotic samples for different magnetite and maghemite diffraction peaks. Same colours and samples as in figure 2.

Mentions: Lattice parameters were calculated based on the assumption of a cubic space lattice (a = b = c; α = β = γ = 90°; a = dhkl/(h2 + k2 + l2)1/2) for all diffraction peaks with considerable intensity greater than 20 counts and well-defined peak shapes. An average lattice parameter was calculated from the obtained values for each sample and the error of the lattice parameter was calculated as standard deviation, as shown later in table 1 and figure 3. Particle sizes were estimated from the peak width after correcting for instrumental broadening effects. Approximating the Bragg peaks by Gaussian profiles, the peak broadening Wtot (full width at half maximum in q-space) can be written as follows [26]:2.1where Wcs corresponds to the crystal size related broadening and W0 depends on the instrumental set-up (beam divergence, detector point spread function and distance). The finite wavelength spread Δλ/λ leads to a q-dependent instrumental broadening. Additional q-dependent contributions owing to possible microstrain fluctuations were not observed and could hence be neglected. If a polycrystalline sample comprising sufficiently large crystals is considered (such as the used NIST standard and the synthetic magnetite and maghemite), the sample-related peak broadening is almost zero and a regression analysis of the q-dependent broadening allows for determining both, W0 and Δλ/λ. The synthetic magnetite sample was used to determine the instrumental broadening, as no differences in Wtotbetween the α-NIST powder and the synthetic magnetite were observed. The obtained values of 0.10266 nm−1 and 0.00167, for W0 and Δλ/λ, respectively, are in good agreement with the beamline performance for a sample to detector distance of approximately 140 mm, a 30 µm beam-defining pinhole and the energy resolution of the Si (111) monochromator. Finally, the particle size (PS) was estimated from Wcs using Scherrer's equation:2.2Table 1.


Structural purity of magnetite nanoparticles in magnetotactic bacteria.

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

Calculated lattice parameters with standard deviations for biotic and abiotic samples for different magnetite and maghemite diffraction peaks. Same colours and samples as in figure 2.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

RSIF20100576F3: Calculated lattice parameters with standard deviations for biotic and abiotic samples for different magnetite and maghemite diffraction peaks. Same colours and samples as in figure 2.
Mentions: Lattice parameters were calculated based on the assumption of a cubic space lattice (a = b = c; α = β = γ = 90°; a = dhkl/(h2 + k2 + l2)1/2) for all diffraction peaks with considerable intensity greater than 20 counts and well-defined peak shapes. An average lattice parameter was calculated from the obtained values for each sample and the error of the lattice parameter was calculated as standard deviation, as shown later in table 1 and figure 3. Particle sizes were estimated from the peak width after correcting for instrumental broadening effects. Approximating the Bragg peaks by Gaussian profiles, the peak broadening Wtot (full width at half maximum in q-space) can be written as follows [26]:2.1where Wcs corresponds to the crystal size related broadening and W0 depends on the instrumental set-up (beam divergence, detector point spread function and distance). The finite wavelength spread Δλ/λ leads to a q-dependent instrumental broadening. Additional q-dependent contributions owing to possible microstrain fluctuations were not observed and could hence be neglected. If a polycrystalline sample comprising sufficiently large crystals is considered (such as the used NIST standard and the synthetic magnetite and maghemite), the sample-related peak broadening is almost zero and a regression analysis of the q-dependent broadening allows for determining both, W0 and Δλ/λ. The synthetic magnetite sample was used to determine the instrumental broadening, as no differences in Wtotbetween the α-NIST powder and the synthetic magnetite were observed. The obtained values of 0.10266 nm−1 and 0.00167, for W0 and Δλ/λ, respectively, are in good agreement with the beamline performance for a sample to detector distance of approximately 140 mm, a 30 µm beam-defining pinhole and the energy resolution of the Si (111) monochromator. Finally, the particle size (PS) was estimated from Wcs using Scherrer's equation:2.2Table 1.

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