Figure 2.

Electron tomography of a 50 nm section of high-pressure frozen and freeze substituted cells. The tilt series was carried out at 120 kV from −60 to +60° with an increment of 2° and a final magnification of 14,000 x. The reconstruction of the tomogram was performed with IMOD. In selected virtual slices, several structures were indicated. (A) The final tomogram revealed the inner (IM) and outer membrane (OM) with a thickness of about 6 nm in each case. The overall thickness of inner and OM together with the periplasm was 44 nm. Therefore, the periplasm has a width of about 32 nm. (B) Further, two hami filaments with a diameter of approximately 8 nm were indicated spanning both the IM and OM (arrow heads). (C) Underneath the IM, another layer could be recognized (arrows). As the resolution of the tomogram is quite low, this could either be kind of an anchoring structure/mechano sensor or a preparation/reconstruction artifact as it was just visible in a very low number of the virtual slices of the tomogram. With this tomogram, a model (segmentation) was constructed (D) illustrating the IM (red) and OM (green), the hami filaments (yellow) and the supposed anchoring-associated structure (blue). For simplicity, the membranes were illustrated as a monolayer. Scale bars: 500 nm.