Fig. 2.

Electron microscopy images of the magnetic protist sampled in the Mediterranean Sea, Carry-le-Rouet. a,b, TEM images showing the ultrastructure of a single magnetic consortium containing about 150 magnetosome chains (a) and a magnetic ectosymbiotic bacterium detached from its host (b). c, TEM image of the longitudinal section through a single magnetic consortium showing the general morphological features of the magnetic protist, such as the nucleus (Nu), a battery of extrusomes (E), the vestibulum (V), the cytostome (Cyt), MEB on the extracellular matrix, the flagellar pocket (FP) with the dorsal and ventral flagella (DF and VF, respectively), hydrogenosomes (H) or mitochondria-like organelles in close vicinity to the ectosymbionts, and digestive vacuoles (Vac) in which grazed magnetotactic bacteria and their magnetosomes can be seen. d, Images of a single magnetic consortium observed using a SEM operating at 2 kV (left) or 10 kV (right) showing the presence of magnetosome chains in the bacteria that cover the protist. e, High-resolution TEM image of a single magnetosome biomineralized by an ectosymbiotic bacterium (top) and the corresponding fast Fourier transform (bottom) for which labelled reflexions have been indexed with respect to the magnetite structure. No octahedral or elongated asymmetric shapes are clearly visible (Supplementary Fig. 3). Scale bars, 2 μm (a,c,d), 0.5 μm (b) and 20 nm (e).