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Biomineralisation of Magnetosomes in Bacteria. Microbial Bionanotechnology Chapter 5. Magnetotactic . Magnetosome Crystalline particles of iron oxide or sulfide Magnetite Fe 3 O 4 Greigite Fe 3 S 4 All are either obligate microaerophiles or strict anaerobes Motile, aquatic bacteria

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Biomineralisation of magnetosomes in bacteria

Biomineralisation of Magnetosomes in Bacteria

Microbial Bionanotechnology

Chapter 5


Magnetotactic
Magnetotactic

  • Magnetosome

    • Crystalline particles of iron oxide or sulfide

    • Magnetite Fe3O4

    • Greigite Fe3S4

  • All are either obligate microaerophiles or strict anaerobes

  • Motile, aquatic bacteria

  • Direction of motility is affected by the Earth’s geomagnetic field

  • Strains are either north- or south-seeking depending upon oxic conditions

    • North-seekers predominate in the northern hemisphere

    • South-seekers predominate the southern hemisphere

    • Exist in equal numbers at the equator

  • Current hypothesis states that these bacteria use the geomagnetic field to locate lower O2 or anaerobic habitats




There are two types of magneto aerotaxis
There are Two Types of Magneto-aerotaxis...

Axial Magneto-aerotaxis

Polar Magneto-aerotaxis

e.g., Magnetospirillum magnetotacticum

e.g., strain MC-1, a magnetotactic coccus


Magnetite Crystals

Produced by

Magnetotactic Bacteria

The MS-1 Genome

Bertani, Weko, Phillips, Gray & Kirschvink,

Physical and genetic characterization of the

Genome of Magnetosprillum Magnetotacticum,

Strain MS-1, Gene 264: 257-263,2001

From http://www.soton.ac.uk/~serg/biotech/mtb-main.htm


Global swimming preferences of magnetotactic bacteria
Global Swimming Preferences of Magnetotactic Bacteria

North-Seeking in the

Northern Hemisphere

(Blakemore, 1975)

N

The equator has

small numbers

Pelau

of both N- and

S-seekers

Equator

(Frankel et al.,

1981; Chang &

Kirschvink, 1989)

S

South-Seeking in the

Southern Hemisphere

(Kirschvink, 1980)

These bugs use the

geomagnetic field as

an up/down indicator

at redox gradients.

Other bugs use tumble-

run random walks.


The kalmijn blakemore 78 pulse remagnetization experiment

100 mT magnetic pulse!

+

=

The remagnetized bacteria roll over and start swimming to the South …

North

South

The Kalmijn-Blakemore (‘78) Pulse-remagnetization Experiment

Start with North-

seeking bacteria

In a weak biasing

Field (~50 uT)

North

South

Hit with a sharp,

antiparallel pulse

exceeding Hc

Unequivocal demonstration of

Single-Domain Ferromagnetism!

Rock Magnetism and Biology!

(Next video Hc = 1/2 Hmx)


Typical bacterial magnetosomes courtesy of h vali
Typical Bacterial Magnetosomes(Courtesy of H. Vali)


3d imaging of bacterial magnetosomes buseck et al pnas 98 13490 13495 2001
3D Imaging of Bacterial MagnetosomesBuseck et al., PNAS 98, 13490-13495, 2001


Higher animals also have magnetosomes
Higher Animals Also Have Magnetosomes

Salmon Magnetosome Chains

(Mann, Sparks, Walker & Kirschvink, 1988)

Human Brain Magnetite

(Kirschvink, Kobayashi & Woodford, 1992)



Biologically important features of magnetosomes darwinian selection for magnetic properties
Biologically Important Features of Magnetosomes: (Darwinian Selection for Magnetic Properties!!!)

  • Size & Shapes with the Single-Domain field

  • Elongation of the ultrafine crystals

  • Orienting [111] axis along length

  • Truncation of ends.

  • Exclusion of Trace Metal Impurities

  • Perfect Crystal Lattice

  • Alignment in chains of similarly-sized particles


Seven criteria for identifying magnetofossils
Seven Criteria for Identifying Magnetofossils*

Particle

Truncated

[111]

Xtl Ends

Elongation

Alignment

Particle

Chains

Chemically

Pure

All Inside the

Intact Crystal

SD Stability

Field

Lattice

*All 7 of these act to maximize the magnetic moment at the cellular level; however, not all magnetofossils will plot in the center


Magnetosomes show the effect of Natural Selection for their magnetic properties. They are just the right size to be perfect biological bar magnets. Any bacterium that makes crystals outside the SD field will die!


Magnetosome elongation by the magnetotactic bacteria
Magnetosome Elongation by the Magnetotactic Bacteria

Octahedral to Centrosymmetric Hexagonal Prisms

(vibroid and coccoid cells)

_

(111)

_

(111)

(111)

_

(111)

(111)

_

_

(111)

(111)

(111)

(111)

_

(111)

_

(111)

_

(111)

_

_

_

_

_

_

_

(011)

_

(111)

(111)

_

(111)

(011)

_

_

_

(111)

Cubo-Octahedral to Elongated Cubo-Octahedral

(100)

(100)

(100)

(100)

(111)

(111)

(111)

(111)

(111)

(010)

(111)

(010)

(010)

(111)

(010)

(111)


BIOGENIC MAGNETITE GEOMETRIES

Blue = {100}

Red = {110}

Green = {111}

{111}  {111} @ 109°

{111}  {100} @ 125°

{111}  {110} @ 145°

{100}  {110} @ 135°

Truncated

Hexaoctahedron

Hexaoctahedron

KT-K


Why should the bacteria truncate the ends of their magnetosomes
Why should the bacteria truncate the ends of their magnetosomes?

Because sharp edges produce magnetic ‘Flower Structures’, which

warp the internal magnetization directions. Putting those iron atoms

in the next crystal increases the magnetic moment of the cells!

See Fabian et al., GJI 124:89-104, 1996; Newell & Merrill JGR 105: 19377-19391)


A PDF file for this model is available on the magnetosomes?

Magnetofossil home page At Caltech

www.gps.caltech.edu/users/jkirschvink/

magnetofossil.html

111

100

110




Magnetotactic bacteria
Magnetotactic Bacteria magnetosomes?

  • Electron cryotomography of Magnetospirillum magneticum sp. AMB-1 reveals that magnetosomes are invaginations of the inner membrane. (A) General features of AMB-1 cells highlighted in a 12-nm-thick section of an ECT reconstruction. Outer membrane, OM; inner membrane, IM; peptidoglycan layer, PG; ribosomes, R; outer membrane bleb, B; chemoreceptor bundle, CR; poly-ß-hydroxybutyrate granule, PHB; gold fiduciary marker, G; magnetosome chain, MG. Scale bar, 500 nm. (B to E) Representative magnetosomes containing no magnetite (B), small (C), mediumsized (D), and fully-grown (E) crystals are invaginations of the inner membrane. Scale bar, 50 nm.


  • Magnetosome magnetosomes? chains are flanked by long cytoskeletal filaments. (A) Larger view of the magnetosome chain in Fig. 1A. (B) Similar view of a magnetosome chain grown in the absence of iron, which prevents the formation of magnetite crystals. Arrows point to the long filaments. (C) Three-dimensional organization of magnetosomes (yellow) and their associated filaments (green) shown in (B) with respect to the whole cell (blue). Scale bars, 100 nm.


Bakterielle magnetosomer
Bakterielle Magnetosomer magnetosomes?

TEM image of two Itaipu-1 cocci. Each bacterium has two chains of magnetosomes (arrows) and two phosphorus-rich globules (P). Scale bar, 1 μm.


High-resolution TEM images of Itaipu-1 magnetosomes with indexed bars parallel to lattice planes. Obvious symmetries between even the very small facets on opposite sides of the crystal diagonals can be seen. Comparison with other crystals of the chain in Fig. 2 also indicates that this symmetry regularly alternates between crystals.


(A) Electrostatic contribution to the holographic phase shift from the Itaipu magnetosomes shown in Fig. 2, oriented to a [110] projection. The contours represent the projected thickness and show a flat-topped morphology and steep sides. (B) Projected thickness contours for the same crystals after tilting by 30° about the chain axis to a [211] orientation. The contours show that the crystal is much thicker along its center than along its edges, having a central ridge formed by intersecting faces. (C) Line profiles (solid line for panel A and dashed line for panel B) across the magnetosomes from the indicated positions (arrows), converted to values of one-half their thickness, reveal a 120° angle between the facets for the [211] projection, which is consistent with the intersection of [110] faces. Scale bar, 150 nm (panels A and B).


  • TEM images of Itaipu-1 and Itaipu-3 shift from the Itaipu magnetosomes shown in Fig. magnetosomes. (A) Chain of large magnetosomes from magnetotactic bacterial strain Itaipu-1 surrounded by smaller, elongated magnetosomes from strain Itaipu-3. The inset is a [211] diffraction pattern from the second large Itaipu-1 crystal (arrow). (B) Same chain as in panel A tilted 30o about the [111] axis. The inset [110] diffraction pattern from the second large Itaipu-1 crystal shows (111) fringes from the magnetically easy axis. Corner faces {111} and {200} are mirrored about the vertical (or horizontal) axis for alternating crystals (double arrows); see detailed image in Fig. 3. Scale bar, 200 nm.


Tomographic reconstruction of a magnetite nanocrystal from an undescribed coccus collected from Sweet Springs Nature Reserve, Morro Bay, CA, reconstructed from a tilt series of STEM HAADF images obtained at 300 kV on a Philips CM300 FEG TEM over a range of ± 56°. The tableau shows the three-dimensional morphology of the crystal viewed from a range of directions.


Magnetosome element analysis
Magnetosome Element Analysis an undescribed coccus collected from Sweet Springs Nature Reserve, Morro Bay, CA, reconstructed from a tilt series of STEM HAADF images obtained at 300 kV on a Philips CM300 FEG TEM over a range of ± 56°. The tableau shows the three-dimensional morphology of the crystal viewed from a range of directions.


Cu fe analysis
Cu-Fe Analysis an undescribed coccus collected from Sweet Springs Nature Reserve, Morro Bay, CA, reconstructed from a tilt series of STEM HAADF images obtained at 300 kV on a Philips CM300 FEG TEM over a range of ± 56°. The tableau shows the three-dimensional morphology of the crystal viewed from a range of directions.


Magnetosomes
Magnetosomes an undescribed coccus collected from Sweet Springs Nature Reserve, Morro Bay, CA, reconstructed from a tilt series of STEM HAADF images obtained at 300 kV on a Philips CM300 FEG TEM over a range of ± 56°. The tableau shows the three-dimensional morphology of the crystal viewed from a range of directions.


Magnetosome crystal morphology
Magnetosome crystal morphology an undescribed coccus collected from Sweet Springs Nature Reserve, Morro Bay, CA, reconstructed from a tilt series of STEM HAADF images obtained at 300 kV on a Philips CM300 FEG TEM over a range of ± 56°. The tableau shows the three-dimensional morphology of the crystal viewed from a range of directions.


  • MamK an undescribed coccus collected from Sweet Springs Nature Reserve, Morro Bay, CA, reconstructed from a tilt series of STEM HAADF images obtained at 300 kV on a Philips CM300 FEG TEM over a range of ± 56°. The tableau shows the three-dimensional morphology of the crystal viewed from a range of directions., a homolog of the bacterial actin-like protein MreB, forms filaments in vivo. (A) Phylogenetic relationship between MamK and other bacterial actin-like proteins demonstrated by an unrooted tree. These proteins separate into three distinct groups: MamK (green), ParM/StbA (red) and MreB (blue). (B) MamK fused to GFP (green) appears to form filaments in vivo localized to the inner curvature of the cell (cell membrane stained red with FM4-64).


  • MamK is required for the proper organization of the magnetosome chain. (A) Three-dimensional reconstruction of a wild-type AMB-1 cell. The cell membrane (gray), magnetosome membrane (yellow), magnetite (orange), and magnetosome-associated filaments (green) are rendered. (B) mamK mutant, where magnetosomes appear disordered and no filaments are found in their vicinity. (C) mamK cell expressing mamK-GFP on a plasmid showing full reversal of the mutant phenotype.


Magnetosome membrane proteins
Magnetosome membrane proteins magnetosome chain. (


Comparative genome analysis
Comparative genome analysis magnetosome chain. (


Magnetotaxis genes
Magnetotaxis genes magnetosome chain. (


Mam gene regulation in cells
Mam gene regulation in Cells magnetosome chain. (


Magnetosome membrane
Magnetosome membrane magnetosome chain. (


Magnetosome membrane protein
Magnetosome membrane protein magnetosome chain. (


Biotechnological applications
Biotechnological applications magnetosome chain. (

  • Delivery systems

  • Separation systems

  • DNA arrays

  • RNA arrays

  • Thermo treatment

  • Sensor systems



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