We describe pulsed-magnetic-field remanence measurements of individual, killed, undisrupted cells of three different types of magnetotactic bacteria. The measurement technique involved the observation of aligned, individual magnetotactic bacteria with a light microscope as they were subjected to magnetic pulses of increasing amplitude. We show that for MM cells, the hysteresis loop is square, with the coercive field variable from cell to cell. This is consistent with just two magnetization states for the single chain of magnetite particles. For MR and MMP cells, the hysteresis loops are not square, indicating that there are several different magnetization states, and that individual cells can be demagnetized. The coercive fields in the MR and MMP cells are less variable than for the MM cells.
Bibliographical noteFunding Information:
We thank J. Hilsinger for help in the construction of the pulsed magnetic field apparatus. IP was supported by a grant from the University of Groningen. DAB and RBF were supported by the U.S. Office of Naval Research. BMM and DAB were supported by the National Science Foundation. Support for the Institute for Rock Magnetism was provided by grants from the Keck Foundation and the National Science Foundation. This is contribution 9409 of the Institute for Rock Magnetism.