Fig. 1

Cryo-EM tomography: a Schematic of single axis cryo-EM tomography. The (small) sample placed on a stage which is progressively tilted along a plane in a typical range of ± 60°, while exposed to an electron beam. Each tilt angle generates a planar projection image, which are collectively processed using an algorithm such as filtered back projection to generate a 3-d reconstruction of the original object. Due to the limited range of tilt angles, the reconstruction doesn’t have uniform resolution across the object. Typically, opposite ends (top and bottom) of the 3-d reconstruction in one direction have poor contrast resolution. b Mid-level cross-section from a 3-d cryo-EM reconstruction of an E. Coli cell. The small enclosures (black arrows) are micro-compartments (MC). The red arrow shows the cell membrane. Note that part of the cell membrane is missing. The scale bar is 200 nm