Fig. 4. False colour transmission electron microscopy image of aligned magnetotactic bacteria. The bacteria are aligned on the TEM grid by the application of a strong external magnetic field. For Magnetospirillum gryphiswaldense, the magnetosome crystals are oriented along the 〈1 1 1〉 crystallographic direction, as depicted on the image. This corresponds to the easy axis of magnetization for isotropic magnetite nanoparticles.¹⁹ .