Dataset Information

Magnetite Crystal Orientation in Magnetosome Chains.

ABSTRACT: One-dimensional magnetic nanostructures have magnetic properties superior to non-organized materials due to strong uniaxial shape anisotropy. Magnetosome chains in magnetotactic bacteria represent a biological paradigm of such magnet, where magnetite crystals synthesized in organelles called magnetosomes are arranged into linear chains. Two-dimensional synchrotron X-ray diffraction (XRD) is applied to cells of magnetotactic bacteria that are pre-aligned with a magnetic field to determine the crystallographic orientation of magnetosomes relative to the chain axis. The obtained pole figure patterns reveal a [111] fiber texture along the chain direction for magnetospirilla strains MSR-1 and AMB-1, whereas a [100] fiber texture is measured for Desulfovibrio magneticus strain RS-1. The [100] axis appears energetically unfavorable because it represents a magnetic hard axis in magnetite, but can be turned into an effective easy axis by particle elongation along [100] for aspect ratios higher than 1.25, consistent with aspect ratios in RS-1 magnetosomes determined earlier. The pronounced fiber textures can be explained either by a strain-specific biological control on crystal orientation at the chain level or by physical alignment effects due to intra-chain magnetic interactions. In this case, biological control of the axis of elongation would be sufficient to influence the crystallographic texture of the magnetosome chain.

SUBMITTER: Kornig A

PROVIDER: S-EPMC4384753 | biostudies-literature | 2014 Jul

REPOSITORIES: biostudies-literature

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Magnetite Crystal Orientation in Magnetosome Chains.

Körnig André A Winklhofer Michael M Baumgartner Jens J Gonzalez Teresa Perez TP Fratzl Peter P Faivre Damien D

Advanced functional materials 20140310 25

One-dimensional magnetic nanostructures have magnetic properties superior to non-organized materials due to strong uniaxial shape anisotropy. Magnetosome chains in magnetotactic bacteria represent a biological paradigm of such magnet, where magnetite crystals synthesized in organelles called magnetosomes are arranged into linear chains. Two-dimensional synchrotron X-ray diffraction (XRD) is applied to cells of magnetotactic bacteria that are pre-aligned with a magnetic field to determine the cry ...[more]

PMID: 25866495

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Project description:Magnetospirillum gryphiswaldense and related magnetotactic bacteria form magnetosomes, which are membrane-enclosed organelles containing crystals of magnetite (Fe3O4) that cause the cells to orient in magnetic fields. The characteristic sizes, morphologies, and patterns of alignment of magnetite crystals are controlled by vesicles formed of the magnetosome membrane (MM), which contains a number of specific proteins whose precise roles in magnetosome formation have remained largely elusive. Here, we report on a functional analysis of the small hydrophobic MamGFDC proteins, which altogether account for nearly 35% of all proteins associated with the MM. Although their high levels of abundance and conservation among magnetotactic bacteria had suggested a major role in magnetosome formation, we found that the MamGFDC proteins are not essential for biomineralization, as the deletion of neither mamC, encoding the most abundant magnetosome protein, nor the entire mamGFDC operon abolished the formation of magnetite crystals. However, cells lacking mamGFDC produced crystals that were only 75% of the wild-type size and were less regular than wild-type crystals with respect to morphology and chain-like organization. The inhibition of crystal formation could not be eliminated by increased iron concentrations. The growth of mutant crystals apparently was not spatially constrained by the sizes of MM vesicles, as cells lacking mamGFDC formed vesicles with sizes and shapes nearly identical to those formed by wild-type cells. However, the formation of wild-type-size magnetite crystals could be gradually restored by in-trans complementation with one, two, and three genes of the mamGFDC operon, regardless of the combination, whereas the expression of all four genes resulted in crystals exceeding the wild-type size. Our data suggest that the MamGFDC proteins have partially redundant functions and, in a cumulative manner, control the growth of magnetite crystals by an as-yet-unknown mechanism.

Project description:To navigate along the earth's magnetic field, magnetotactic bacteria (MTB) biomineralize iron in unique organelles, the magnetosomes, which are highly ordered, membrane-enclosed, nano-sized crystals of magnetite or greigite1. Magnetosome biogenesis was recently found to be controlled by a large set of genes clustered within a genomic magnetosome island. The unprecedented structural and magnetic properties of magnetosomes and the difficulties to cultivate and manipulate the fastidious bacteria have stimulated ideas to express the underlying biosynthesis pathway in more amenable hosts. However, this has remained an unsolved challenge, owing to the structural complexity of the magnetosome organelle, the insufficient knowledge of involved gene functions, and the challenge to balance expression of numerous proteins. Here we show that the entire gene set required for magnetosome biogenesis can be functionally expressed in the model organism Rhodospirillum rubrum, thereby converting it into a synthetic magnetotactic and phototrophic bacterium. Modular transfer of various cassettes comprising the 30 mam and mms genes that were stitched together by recombinogenic cloning was required and sufficient for biogenesis of magnetosome chains in R. rubrum. However, further auxiliary functions encoded outside these clusters were necessary for biosynthesis of fully developed magnetosomes. Our results for the first time demonstrate that the synthesis of one of the most complex prokaryotic structures can be fully reconstituted within a foreign, hitherto nonmagnetic host. We provide first experimental evidence that the magnetotactic trait can be transmitted horizontally to different species by single or few events of transfer. Conceivably, our findings may enable future synthetic biology approaches for the endogenous production of tailored magnetic nanoparticles within both prokaryotic and eukaryotic organisms, which will be useful for various biotechnological and biomedical applications. Spectra were analyzed via MascotTM software using the NCBI nr Protein Database and a database from M. gryphiswaldense (Richter et al., 2007). Database : Proteindatabase from Richter et al. 2007. Enzyme : Trypsin/P. Fixed modifications : Carbamidomethyl (C). Variable modifications : Oxidation (M). Mass values : Monoisotopic. Protein Mass : Unrestricted. Peptide Mass Tolerance : +/- 10 ppm. Fragment Mass Tolerance: +/- 0.8 Da. Max Missed Cleavages : 2. Instrument type : Default. Number of queries : 4310. Database : NCBInr 201102 (13043846 sequences; 4463804608 residues). Taxonomy : Other Proteobacteria (1938652 sequences). Mascot Version: 2.3.02.

Dataset Information

Magnetite Crystal Orientation in Magnetosome Chains.

Publications

Magnetite Crystal Orientation in Magnetosome Chains.

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