Migration rate of mud bacteria as a function of magnetic field strength

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1980-11Author
Teague, Barbara D.
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Gilson, Michael
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Kalmijn, Adrianus J.
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https://hdl.handle.net/1912/9593DOI
10.1575/1912/9593Keyword
Bacteria; Magnetic fieldsAbstract
Certain marine and freshwater mud bacteria are endowed with a permanent magnetic
dipole moment. This moment is attributed to an endogenous chain of tightly coupled, single-domain
magnetite crystals. When separated from the mud, these magnetic bacteria swim
north, following the earth's magnetic field lines. As at Woods Hole, Massachusetts, the
field lines are steeply vertically inclined, the bacteria rapidly return to the bottom substrate
where they seem to thrive best. To quantify this migration, we measure the time to
traverse the distance between two lines, 1 mm apart, as a function of the ambient magnetic
field strength. Using dark-field illumination, we observe single organisms as they migrate
in a low-oxygen hemocytometer chamber. We control the ambient magnetic field by regulating
the current through a Helmholtz-coil system. At high magnetic field strengths, the bacteria
follow a virtually straight path, swimming at rates around 150 µm/sec. At lower field strengths,
they take a more random path which reduces their migration rate. Although they swerve
moderately at the earth's magnetic field strength (0.5 gauss) , the bacteria still achieve about
80% of their maximum migration rate observed at higher-gauss fields. This suggests that
the bacterial dipole moments are well adapted to orientation in the earth's magnetic field.
Since the strength of their magnet determines the degree to which the organisms overcome
random motion, we can estimate the magnitude of their dipole moment.
Description
Also published as: The Biological Bulletin 157 (1979): 399
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Suggested Citation
Teague, B. D., Gilson, M., & Kalmijn, A. J. (1980). Migration rate of mud bacteria as a function of magnetic field strength. Woods Hole Oceanographic Institution. https://doi.org/10.1575/1912/9593Related items
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