912 omega

For electron microscopy, M. magneticum cells were concentrated by centrifugation (5000 rpm, 5 min, 4°C), adsorbed onto a cooper grid, rinsed once with buffer (10 mM Hepes, 5 mM EDTA) and once with distilled water. The samples were imaged using a Zeiss 912 Omega transmission electron microscope at 120 kV.
The transmission electron microscopy images were analyzed with “ImageJ” in order to determine the size of magnetosomes, their amount per cell and the cell length (Supplementary Figures S2B–F). The magnetosomes dimensions were estimated by calculating the best fit of ellipse to the contours (Devouard et al., 1998 (link)).

Electron microscopy was carried out as described previously (Agbulut et al., 2001 (link); Joanne et al., 2013 (link)). Briefly, the calf muscles of mice were fixed in 2% glutaraldehyde and 2% paraformaldéhyde in 0.2 M phosphate buffer at pH 7.4 for 1 h at room temperature. After 1 h, the plantaris muscle was dissected and separated in three by a short-axis section, then fixed overnight at 4°C in the same fixative. After washing, specimens were post-fixed for 1 h with 1% osmium tetroxide solution, dehydrated in increasing concentrations of ethanol and finally in acetone, and embedded in epoxy resin. The resin was polymerized for 48 h at 60°C. Ultrathin sections (70 nm) were cut with an ultramicrotome (Leica UC6, Leica Microsystems), picked-up on copper rhodium-coated grids and stained for 2 min with Uranyl-Less solution (Delta Microscopies, France) and 2 min with 0.2% lead citrate before observation at 80 kV with an electron microscope (912 Omega, Zeiss) equipped with a digital camera (Veleta 2kx2k, Emsis, Germany).

The bacterial cells suspension were diluted in nutrient broth (NB) to 0.5 McFar-land’s standard and treated accordingly with MIC of artonin E for 24 h at 37°C. These cells were consequently fixed with 4% glutaraldehyde, then post-fix for 15 hour in 1% osmium tetroxide. Graded ethanol series were used to dehydrate the samples prior to washing with propylene oxide-epon. Ultrathin 100 nm sectioning was prepared and stained with 3% uranyl acetate. Samples were viewed using Zeiss 912 Omega (Oberkochen, Germany) microscope.