The S pole distribution on magnetic grains in pyroxenite determined by magnetotactic bacteria

Minoru Funaki*, Hideo Sakai, Tadashi Matsunaga, Shigehisa Hirose

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


North-seeking bacteria (NSB) with 1 μm diameters migrate to the S pole only. They were applied to identify the S pole determination on a polished surface of magnetite-rich pyroxenite whose natural remanent magnetization (NRM) intensity was 5.64 × 10-3 Am2 kg-1. The microscopic observations were performed under dark-field illumination in a controlled magnetic field to 10 μT. The NSB formed clusters on limited areas of magnetite grains and scattered over the whole magnetite grains. The NRM decreased to 1.02 × 10-5 Am2 kg-1 by alternating field (AF) demagnetization to 60 mT but no clusters appeared, while small populations of the NSB scattered on each grain. These scattered bacteria may gather toward the S pole resulting from magnetic domain walls. When the sample acquired saturation isothermal remanent magnetization (SIRM) to 1 T, the NSB formed dense clusters at the opposite side to the applied field direction on the many grains as expected. This evidence indicated that the NSB can be useful micro-organisms for the determination of fine magnetic structures. Some grains also had NSB clusters at the edge of the grains toward the field direction or did not exhibit any clusters. The complicated distribution of the clusters (the S poles) may be explained by shape anisotropy of the magnetic grains.

Original languageEnglish
Pages (from-to)253-260
Number of pages8
JournalPhysics of the Earth and Planetary Interiors
Issue number3-4
Publication statusPublished - 1992
Externally publishedYes

ASJC Scopus subject areas

  • Geophysics
  • Space and Planetary Science
  • Physics and Astronomy (miscellaneous)
  • Astronomy and Astrophysics
  • General Earth and Planetary Sciences
  • General Environmental Science


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