Below is the Journal of Microscopy abstract.
Journal of Microscopy
Volume 213 Issue 2 Page 180 - February 2004
doi:10.1111/j.1365-2818.2004.01287.x
Magnetosomal matrix: ultrafine structure may template biomineralization of
magnetosomes
A. P. Taylor* & J. C. Barry
Summary
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.
Keywords: ALH84001, biomineralization, biosignature, greigite, magnetite,
magnetofossils, magnetosomal, matrix, magnetosomal membrane, magnetosomes,
TEM
Received 31 October 2001; accepted 30 September 2003
Affiliations
*Department of Microbiology and Parasitology and Centre for Microscopy
and Microanalysis,
The University of Queensland,
Brisbane, QLD, 4072, Australia
Correspondence
Correspondence to:
Dr Tony Taylor,
Materials and Engineering Science,
Australian Nuclear Science and
Technology Organization
(ANSTO), PMB 1, Menai, Sydney,
NSW, 2234, Australia. E-mail: [EMAIL PROTECTED]
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