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Biomineralisation of Magnetosomes in Bacteria Microbial Bionanotechnology Chapter 5 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 2 Types of magnetotaxis Types of magneto-aerotaxis There are Two Types of Magnetoaerotaxis... Axial Magnetoaerotaxis e.g., Magnetospirillum magnetotacticum Polar Magnetoaerotaxis e.g., strain MC-1, a magnetotactic coccus 5 Magnetite Crystals Produced by Magnetotactic Bacteria Pc2 Sw3 Pm3 Pm2 Sw7 dnaA st p2 Sw6 bf r1, bf r2, nm1, st p1 magA, st p5 Sw1 ~4. 3 mb st p3, st p4 dms, f dx Pm4 ni f l 1, rpl 6, Sw2 rpoA f t sH, ni f L2 Sw5 napA, rrn2, sodB Sw4 Pc1 Pm1 The MS-1 Genome From http://www.soton.ac.uk/~serg/biotech/mtb-main.htm Bertani, Weko, Phillips, Gray & Kirschvink, Physical and genetic characterization of the Genome of Magnetosprillum Magnetotacticum, Strain MS-1, Gene 264: 257-263, 2001 Global Swimming Preferences of Magnetotactic The equator has Bacteria North-Seeking in the Northern Hemisphere (Blakemore, 1975) N Pelau Equator small numbers of both N- and S-seekers These bugs use the (Frankel et al., 1981; Chang & geomagnetic field as Kirschvink, 1989) an up/down indicator at redox gradients. S South-Seeking in the Southern Hemisphere (Kirschvink, 1980) Other bugs use tumblerun random walks. The Kalmijn-Blakemore (‘78) Pulseremagnetization Experiment Start with Northseeking bacteria In a weak biasing Field (~50 uT) Hit with a sharp, antiparallel pulse exceeding Hc North South 100 mT magnetic pulse! + = The remagnetized bacteria roll over and start swimming to the South … North South Typical Bacterial Magnetosomes (Courtesy of H. Vali) 3D Imaging of Bacterial Magnetosomes Buseck et al., PNAS 98, 13490-13495, 2001 Higher Animals Also Have Magnetosomes Salmon Magnetosome Chains Human Brain Magnetite (Mann, Sparks, Walker & Kirschvink, 1988) (Kirschvink, Kobayashi & Woodford, 1992) MV-1 and Magnetofossils 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 Truncated Xtl Ends Particle Elongation [111] Alignment Seven Criteria for Identifying Magnetofossils* *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! 5 Two- Domai n I nt er act i on st abi l i zed 1 Bact er i a 10 Pr ot i st s I sol at ed cr yst al s Si ngl eDomai n 0. 1 4 10 Pi geons Bact er i a 3 MS- 1 Fi sh, Human Super par amagnet i c . 001 0. 0 0. 2 0. 4 0. 6 0. 8 10 1. 0 Wi dt h/ Lengt h 2 Lengt h ( A) 10 o Lengt h ( um) 10 Magnetosome Elongation by the Magnetotactic Bacteria Octahedral to Centrosymmetric Hexagonal Prisms (vibroid and coccoid cells) _ _ (111) _ (111) (111) _ (111) __ (111) _ (111) (111) _ (111) __ _ (111) (011) (111) _ (111) _ __ (111) (111) (111) _ (111) _ (011) _ __ (111) Cubo-Octahedral to Elongated Cubo-Octahedral BIOGENIC MAGNETITE GEOMETRIES Blue = {100} Red = {110} Green = {111} {111} {111} @ 109° {111} {100} @ 125° {111} {110} @ 145° {100} {110} @ 135° Hexaoctahedron KT-K Truncated Hexaoctahedron 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 Magnetofossil home page At Caltech www.gps.caltech.edu/users/jkirschvink/ magnetofossil.html 111 100 110 Martian Magnetofossil (enlarged ~1,600,000 times) Modeled after K. Thomas-Keprta et al. PNAS 98: 2165, 200 Iron Uptake & Purification in the Magnetotactic Bacteria Source Rock Ma g n e t o s o me Me mb r a n es 3+ 2+ I ron (Fe and Fe ) Ot her Cat i ons Trans-membrane i ron channel (mag-A?) Si derophores Transf erri n Ce l l me mb r a n e Biomineralisation of Fe Magnetotactic Bacteria • 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 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 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 onehalf 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 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 Cu-Fe Analysis Magnetosomes Magnetosome crystal morphology • MamK, 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 Comparative genome analysis Magnetotaxis genes Mam gene regulation in Cells Magnetosome membrane Magnetosome membrane protein Biotechnological applications • • • • • • Delivery systems Separation systems DNA arrays RNA arrays Thermo treatment Sensor systems Applications of Magnetosome particles