Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published November 1991 | Published
Journal Article Open

Alteration of the Magnetic Properties of Aquaspirillum magnetotacticum by a Pulse Magnetization Technique


The presence of a narrow shape and size distribution for magnetite crystals within magnetotactic organisms suggests strongly that there are species-specific mechanisms that control the process of biomineralization. In order to explore the extent of this control, cultures of Aquaspirillum magnetotacticum in the exponential growth phase were exposed to increasing magnetic pulses with the aim of separating cell populations on the basis of their magnetic coercivities. Isothermal remanent magnetization and anhysteretic remanent magnetization studies were performed with freeze-dried magnetic cells after the remagnetization treatment. Subpopulations of A. magnetotacticum that showed an increase in coercivity correlated with the intensity of the magnetic pulses were isolated. After successive subcultures of the remaining north-seeking cells, a maximum bulk coercivity (H_b^(max)) of 40 mT was obtained after treatment with a 55-mT pulse. Although we obtained A. magnetotacticum variants displaying higher coercivities than the wild-type strain, changes in crystal size or shape of the magnetite crystals were below reliable detection limits with transmission electron microscopy. Attempts to shift the coercivity towards higher values caused it to decrease, a change which was accompanied by an increase in magnetostatic interactions of the magnetosome chains as well as an increase in the cell population displaying an abnormal distribution of the magnetosome chains. Ultrastructural analyses of cells and magnetosomes revealed the appearance of cystlike bodies which occasionally contained magnetosomes. The increase in cystlike cells and abnormal magnetosome chains when higher magnetic pulses were used suggested that magnetosomes were collapsing because of stronger interparticle magnetostatic forces.

Additional Information

© 1991 American Society for Microbiology. Received 28 May 1991. Accepted 26 August 1991. This work was supported by a grant from the Caltech Consortium in Chemistry and Chemical Engineering. We thank M. Nesson for his helpful comments and suggestions. Contribution no. 5026 of the Division of Geological and Planetary Science.

Attached Files

Published - DIAaem91.pdf


Files (2.2 MB)
Name Size Download all
2.2 MB Preview Download

Additional details

August 20, 2023
October 17, 2023