Imaging bacteria inside their host by cryo-focused ion beam milling and electron cryotomography.

Bacterium-host interactions are important for diverse ecological settings including pathogenicity and symbiosis. Electron cryotomography is a powerful method for studying the macromolecular complexes that mediate such interactions in situ. The main limitation of electron cryotomography is its restriction to relatively thin samples such as individual bacterial cells. Cryo-focused ion beam milling was recently proposed as a solution to the thickness limitation. This approach allows the artifact-free thinning of biological specimens for subsequent imaging in the transmission electron microscope. By enabling near-native imaging of bacteria inside their eukaryotic host, this combination of techniques promotes the integration of data from structural biology and infection biology. Therefore, electron cryotomography associated with cryo-focused ion beam milling holds great potential for establishing multiscale models of cell-cell interactions from the atomic, to the cellular and to the intercellular scale.