Magnetosomal matrix: ultrafine structure may template biomineralization of magnetosomes

Taylor, A. P. and Barry, J. C. (2004) Magnetosomal matrix: ultrafine structure may template biomineralization of magnetosomes. Journal of Microscopy-oxford, 213 2: 180-197. doi:10.1111/j.1365-2818.2004.01287.x

Author Taylor, A. P.
Barry, J. C.
Title Magnetosomal matrix: ultrafine structure may template biomineralization of magnetosomes
Journal name Journal of Microscopy-oxford   Check publisher's open access policy
ISSN 0022-2720
Publication date 2004
Sub-type Article (original research)
DOI 10.1111/j.1365-2818.2004.01287.x
Volume 213
Issue 2
Start page 180
End page 197
Total pages 18
Place of publication UK
Publisher Blackwell
Collection year 2004
Language eng
Subject C1
259999 Chemical Sciences not elsewhere classified
780103 Chemical sciences
Abstract The organic matrix surrounding bullet-shaped, cubo-octahedral, D-shaped, irregular arrowhead-shaped, and truncated hexa-octahedral magnetosomes was analysed in a variety of uncultured magnetotactic bacteria. The matrix was examined using low- (80 kV) and intermediate- (400 kV) voltage TEM. It encapsulated magnetosomes in dehydrated cells, ultraviolet-B-irradiated dehydrated cells and stained resin-embedded fixed cells, so the apparent structure of the matrix does not appear to be an artefact of specimen preparation. High-resolution images revealed lattice fringes in the matrix surrounding magnetite and greigite magnetosomes that were aligned with lattice fringes in the encapsulated magnetosomes. In all except one case, the lattice fringes had widths equal to or twice the width of the corresponding lattice fringes in the magnetosomes. The lattice fringes in the matrix were aligned with the {311}, {220}, {331}, {111} and {391} related lattice planes of magnetite and the {222} lattice plane of greigite. An unidentified material, possibly an iron hydroxide, was detected in two immature magnetosomes containing magnetite. The unidentified phase had a structure similar to that of the matrix as it contained {311}, {220} and {111} lattice fringes, which indicates that the matrix acts as a template for the spatially controlled biomineralization of the unidentified phase, which itself transforms into magnetite. The unidentified phase was thus called pre-magnetite. The presence of the magnetosomal matrix explains all of the five properties of the biosignature of the magnetosomal chain proposed previously by Friedmann et al. and supports their claim that some of the magnetite particles in the carbonate globules in the Martian meteorite ALH84001 are biogenic. Two new morphologies of magnetite magnetosomes are also reported here (i.e. tooth-shaped and hexa-octahedral magnetosomes). Tooth-shaped magnetite magnetosomes elongated in the [110] direction are reported, and are distinct from arrowhead-shaped and bullet-shaped magnetosomes. Elongation of magnetite magnetosomes in the [110] direction has not been reported previously. A Martian hexa-octahedral magnetite particle was previously characterized by Thomas-Keptra et al. and compared with truncated hexa-octahedral magnetite magnetosomes. Hexa-octahedral magnetite magnetosomes with the same morphology and similar sizes and axial ratios as those reported by Thomas-Keptra et al. are characterized here. These observations support their claim that ALH84001 contains evidence for a past Martian biota.
Keyword Microscopy
Magnetosomal Matrix
Magnetosomal Membrane
Martian Meteorite Alh84001
Atomic-force Microscopy
Magnetotactic Bacteria
Magnetite Crystals
Biogenic Magnetite
Sedimentary Environments
Greigite Fe3s4
Q-Index Code C1

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Created: Wed, 15 Aug 2007, 04:54:29 EST