REMANENCE MEASUREMENTS ON INDIVIDUAL MAGNETOTACTIC BACTERIA USING A PULSED MAGNETIC-FIELD

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 aligne d, individual magnetotactic bacteria with a light microscope as they w ere 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 magnetiza tion states for the single chain of magnetite particles. For MR and MM P cells, the hysteresis loops are not square, indicating that there ar e several different magnetization states, and that individual cells ca n be demagnetized. The coercive fields in the MR and MMP cells are les s variable than for the MM cells.