Magnetotaxis

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The orientation of the direction of movement of living beings in a magnetic field is called magnetotaxis . Orientation ( taxis ) on the earth's magnetic field is ecologically important . According to current knowledge, magnetosomes can play a role in this. Magnetosomes have their own magnetism and tend to align in magnetic fields. In contrast to chemotaxis or phototaxis , only initial indications of a sensory system have been found for the iron mineral-based magnetic sense .

Structure and morphology of magnetosomes

Magnetosomes consist of membrane-surrounded magnetite (Fe III 2 Fe II O 4 ) or greigite crystals (Fe III 2 Fe II S 4 ) and have a diameter of about 40 to 90 nm. Contrary to what is often said in textbooks, the surrounding membrane consists of one of lipid bilayer derived from the cytoplasmic membrane . This was confirmed by the analysis of the lipid components and observation of magnetosome vesicles budding from the cytoplasmic membrane. The shape of the magnetosomes varies greatly between different species. It can be cube-shaped to cuboid and also nail-shaped or teardrop-shaped. Each cell contains several magnetosomes that form chains in it.

Distribution and ecological importance in bacteria

Magnetospirillum gryphiswaldense cells that contain chains of intracellular magnetite crystals (top). Magnetite crystals formed
by M. gryphiswaldense (below).
(both electron microscope images)

Magnetotaxis in bacteria was first described in 1975 by Richard P. Blakemore in Science .

Magnetotactic bacteria live in bodies of water ( aquatic ) and are adapted to low oxygen concentrations ( microaerophilic ). They move with the help of flagella and have magnetosomes inside them, which are arranged in a row. Most of the magnetotactic bacteria are spirilla , an example of the species Magnetospirillum gryphiswaldense , Magnetospirillum magnetotacticum , Aquaspirillum magnetotacticum .

Magnetosomes give the cell simple magnetic properties, whereby the bacteria are aligned parallel to the lines of force of the earth's magnetic field. The polarity of magnetotactic bacteria on the northern half of the earth is so oriented that they move towards the magnetic north pole when swimming. Because of the inclination of the earth's magnetic field outside the equatorial region, the movement is directed obliquely downwards. Magnetotactic bacteria in the southern half of the earth do the same by aligning the polarity so that they move towards the south magnetic pole.

This downward movement causes the bacteria to reach the boundary layer of the water just above the sediment over a short distance . There, because of the higher oxygen consumption when organic substances are broken down in the sediment, the oxygen concentration is low. In addition, organic substances are available in higher concentrations in this area than in higher water layers. These are favorable conditions for the heterotrophic microaerophilic bacteria.

An alternative to magnetotaxis is chemotaxis , which can lead to the same goal in non-magnetotactic bacteria. However, chemotaxis is based on the principle of “trial and error”, so that chemotactic bacteria only reach their destination in a roundabout way.

Other occurrences

The Phyto flagellate Anisonaema (Euglenophyceae), which can be found in Brazilian coastal waters, can also use magnetosomes to orient itself to the Earth's magnetic field, as can green algae ( Volvox aureus , Palmer 1963) and plants.

In some higher living things, including vertebrates , magnetosomes have been found in the area of ​​the ears or in the brain. It is believed that they play a role in orienting the movement of these living things.

When analyzing satellite photos in 2008 it was found that cattle , deer and roe deer prefer to graze in a north-south direction. Under high-voltage lines running in a south-east or north-west direction, however, the orientation was random. The interpretation of these findings was initially controversial (for details see Magnetsinn # Cattle and Deer ). However, observations by Oldenburg biologists on robins have shown that man-made electromagnetic fields can also disrupt the orientation of migratory birds in the earth's magnetic field.

Geoscientific importance

The ability of magnetotactic bacteria is used in magnetostratigraphy to reconstruct the polarity of the magnetic field in the history of the earth. Because after the bacteria have died and become fixed in the sediment, the susceptible chains of magnetite crystals preserve the polarity and inclination of the magnetic field at a certain time in the history of the earth.

In the geomagnetic prospecting of archaeological sites , the concentration of magnetite crystals in organic materials previously decomposed by magnetotactic bacteria can be demonstrated. B. post holes, garbage pits or filled trenches can be detected in Neolithic (Neolithic) settlements.

In the art, the particularly effectively magnetized microscopic grains are of interest for data storage.

literature

  • Stephen Mann, Nick HC Sparks, and Ron G. Board: Magnetotactic Bacteria: Microbiology, Biomineralization, Palaeomagnetism and Biotechnology. In: Advances in Microbial Physiology. Volume 31, 1990, pp. 125-181, doi: 10.1016 / S0065-2911 (08) 60121-6 .
  • Christopher T. Lefèvre, Dennis A. Bazylinski: Ecology, Diversity, and Evolution of Magnetotactic Bacteria. In: Microbiology and Molecular Biology Reviews. Volume 77, No. 3, 2013, pp. 497-526, doi: 10.1128 / MMBR.00021-13 .

See also

Web links

  • Ask the Lesch video contribution to the 2011 Magnetotaxis study.

Individual evidence

  1. ↑ Dominik Heyers, Manuela Zapka, Mara Hoffmeister, John Martin Wild and Henrik Mouritsen : Magnetic field changes activate the trigeminal brainstem complex in a migratory bird. In: PNAS. Volume 107, No. 20, 2010, pp. 9394-9399, doi: 10.1073 / pnas.0907068107 .
    Migratory birds have two magnetic senses. On: idw-online.de from April 5, 2010.
  2. ↑ Yuri A. Gorby, Terry J. Beveridge, Richard P. Blakemore: Characterization of the bacterial magnetosome membrane. In: Journal of bacteriology . Vol. 170, No. 2, 1988, pp. 834-841, PMC 210730 (free full text).
  3. ↑ Karen Grünberg, Eva-Christina Müller, Albrecht Otto, Regina Reszka, Dietmar Linder, Michael Kube, Richard Reinhardt, Dirk Schüler: Biochemical and Proteomic Analysis of the Magnetosome Membrane in Magnetospirillum gryphiswaldense. In: Applied and Environmental Microbiology. Vol. 70, No. 2, February 2004, pp. 1040-1050.
  4. ↑ Arash Komeili, Zhuo Li, Dianne K. Newman, Grant J. Jensen: Magnetosomes are cell membrane invaginations organized by the actin-like protein MamK. In: Science. Vol. 311, No. 5758, 2006, pp. 242-245, PMID 16373532 .
  5. ^ Richard P. Blakemore: Magnetotactic bacteria. In: Science. Volume 190, No. 4212, 1975, pp. 377-379, doi: 10.1126 / science.170679 .
  6. ^ University of Marburg , accessed on December 17, 2011.
  7. ↑ Martin Dworkin, Stanley Falkow, Eugene Rosenberg, Karl-Heinz Schleifer , Erko Stackebrandt (Eds.): The Prokaryotes - A Handbook on the Biology of Bacteria. Vol. 2: Ecophysiology and Biochemistry. 3rd edition, Springer Verlag, New York 2006, ISBN 978-0-387-25492-0 , p. 844, limited preview in the Google book search.
  8. ^ University of Marburg , accessed on December 17, 2011.
  9. ^ Galland, Mazur: Magnetoreception in plants ; Facsimile In: J. Plant Res. 118, 2005, pp. 371-389, accessed December 17, 2011.
  10. Jump up ↑ Sabine Begall , Jaroslav Červený, Julia Neef, Oldřich Vojtčch, Hynek Burda: Magnetic alignment in grazing and resting cattle and deer. In: PNAS. Volume 105, No. 36, pp. 13451-13455, 2008, doi: 10.1073 / pnas.0803650105 .
  11. ↑ Svenja Engels et al .: Anthropogenic electromagnetic noise disrupts magnetic compass orientation in a migratory bird. In: Nature. Volume 509, 2014, pp. 353-356, doi: 10.1038 / nature13290 .
    Confused fluttering in the electrosmog. On: zeit.de from May 8, 2014