Magnetotactic bacteria and their biominerals

Taylor, A.P. (2002). Magnetotactic bacteria and their biominerals PhD Thesis, School of Molecular and Microbial Sciences, The University of Queensland.

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Author Taylor, A.P.
Thesis Title Magnetotactic bacteria and their biominerals
School, Centre or Institute School of Molecular and Microbial Sciences
Institution The University of Queensland
Publication date 2002
Thesis type PhD Thesis
Supervisor John C. Barry
A. Chris Hayward
Horst Doelle
Total pages 380
Collection year 2002
Language eng
Subjects L
270301 Bacteriology
780105 Biological sciences
Formatted abstract
In this study, a variety of new techniques were developed to facilitate the study of magnetotactic responses, the collection of magnetotactic bacteria from environmental samples and to prepare them for analytical transmission electron microscopy (ATEM). A magnetic harvest technique developed here, employed changing the orientation of a weak magnetic field to focus magnetotactic cells on the sides of a harvest vessel and then forced them to swim parallel to the sides, to the top where they were collected. This technique minimised their contact with suspended sediment particles and the sides of the harvest vessel and yielded 109-1010 magnetotactic cells, with up to 20 morphologically distinct strains of magnetotactic bacteria, from relatively large quantities of suspended sediment (5.0 1) in a four-phase process.

3-aminopropyl triethoxy silane (APTES)-primed ultraviolet-B (UV-B)-irradiated PioloformTM (P*A) was more adhesive to cells than the most commonly used support films primed with carbon and poly-L-lysine. UV-B-irradiation of dehydrated cells adhered to P*A in the presence of air, induced a remarkable degree of stability, when exposed to a condensed electron beam, which facilitated the acquisition of phase-contrast lattice images with d values of 1.1 and 1.2 Å, which was less than half the width of the smallest fringes reported previously in similar specimens.

Using magnetosomal morphology, cellular ultrastructure and the habitat from which the cells came, 80 potentially different strains of magnetotactic bacteria were identified in the Moreton Bay region of Australia. There were 41 marine, 5 brackish and 34 freshwater strains differentiated. Nine types of magnetosome were analysed, with four types having idealised morphologies that have not been reported previously, including: irregularly truncated octahedral magnetite elongated in the [ 2 1 1 ] direction, with D-shaped projections; arrowhead-shaped magnetite with a single { 1 0 0} face on the wide end, with pick-shaped projections; arrowhead-shaped magnetite elongated bidirectionally, with centrosymmetric projections; and cubic magnetite elongated in the [ 1 10] direction, with tooth-shaped projections.

A variety of magnetite magnetosomes with anomalous morphologies and structures were analysed here. Many of these structures resembled the magnetite particles in the Martian meteorite ALH84001 (McKay et al. 1996a). These anomalous nanophase magnetite particles had previously been reported as evidence of crystallisation from a super-heated fluid or vapour-phase growth by Bradley et al. (1996). Magnetite magnetosomes with axial ratios of 6:1, screw dislocations, irregular and spinel-law twinning, higher order { 2 1 1 } and { 5 1 1} faces, jagged and undulated faces, as well as lattice disorder and oxygen deficiencies in magnetite magnetosomes are also reported here. Observations were made of: the coprecipitation of a Ca-O-rich precipitate, possibly calcium carbonate (CaCO₃), with a variety of magnetite magnetosomes; the coprecipitation of a Si-0-rich precipitate, possibly amorphous silica (SiO₂), with magnetite magnetosomes; and the accumulation of Ti, Zn, Mg, Ca and Al in phosphorous- rich inclusions, collectively account for the concurrence and arrangement of nanophase magnetite, metal-carbonates and silica in ALH84001. One small magnetotactic spirillum produced magnetite magnetosomes with the same zone axis projections as does the hexaoctahedral magnetite in ALH84001. Collectively, this provide strong evidence supporting the claims that ALH84001 contains magnetofossils within biogenic carbonate concretions.

Some immature bullet-shaped and tooth-shaped magnetosomes, were possibly composed of an unidentified phase, as well as magnetite. The unidentified phase was an iron oxide or hydroxide. It was hypothesised to be the precursor in the biomineralization of magnetite and was called here pre-magnetite.

Low magnification and high resolution images of unstained dehydrated magnetotactic cells adhered to a variety of support films, with and without UV-B-irradiation, contained evidence of a magnetosomal matrix. Stained ultrasections of resin-embedded cells also contained evidence of the matrix. The matrix was 20-70 nm thick and surrounded bullet-shaped, cubooctahedral, D-shaped, irregular arrowhead-shaped and pseudo-hexagonal prismatic magnetite magnetosomes, as well as greigite magnetosomes. Lattice fringes were detected in the magnetosomal matrices surrounding a variety of magnetite magnetosomes and a greigite magnetosome in a variety of strains. The lattice fringes were aligned with and had widths that correlated with lattice planes in the magnetosomes. Lattice fringes oriented with the { 3 1 1 }, { 2 2 0 } , { 1 1 1 } , { 3 3 1 } and {391} lattice planes of magnetite magnetosomes and aligned with the { 2 2 2 } lattice plane of greigite magnetosomes, were recorded. {31 1 }, { 2 2 0 } and { 1 1 1 } lattice fringes were detected in pre-magnetite. This indicates that the magnetosomal matrix may act as a mother matrix for the precipitation of pre-magnetite, which transforms into magnetite.

The structures of iron-sulfide magnetosomes were also analysed here. Without UV-Birradiation, iron-sulfide magnetosomes were unstable under an electron beam and appeared to rapidly transform into compounds consistent with those reported by others (Mann et al. 1990b, Farina et al. 1990 and Pósfai et al. 1998a and b), which explains the contradictory reports by these authors. UV-B-irradiated iron-sulfide magnetosomes did not develop planar contrasted features within their structures and were composed of greigite solely or greigite and an unidentified surface phase, termed here pre-greigite, which is hypothesised to be a precursor in the biomineralization of greigite, because it was only detected on magnetosomes with sizes that correlated to growth. Pre-greigite is hypothesised here to be composed of a compressed form of cubic iron sulfide (d₁₁₁ = 3.06 Å) and an expanded form of mackinawite (d0₁₁ = 3.03 Å).
Keyword Marine biology.
Freshwater biology.

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Fri, 24 Aug 2007, 17:52:30 EST