Pulsed-field-remanence measurements on individual magnetotactic bacteria

We measured pulsed-magnetic-field remanences of individual cells of two types of magnetotactic bacteria. Wild-type magnetic vibrios displayed square remanence curves with the reversal field, H-rev reaching values up to 825 Oe (65.7 kA/m). We attribute the generally high values of H-rev to the elongated shape of the magnetosomes (length-to-width ratio, e approximate to 1.2) and to the comparatively short distances between the magnetosomes (8 nm). Cells of the rod-shaped Magnetobacterium bavaricum, on the other hand, which frequently contain more than 600 magnetosomes per cell, could gradually be demagnetised; the coercivity of remanence, H-cr of individual cells always ranged between 600 and 700 Oe (47.7-55.7 kA/m). The non-square remanence curves of M. bavaricum reflect a distribution of elongations and interactions between adjacent strands of magnetosomes within the braid-like chains. (C) 2002 Elsevier Science B.V. All rights reserved.