Figure 5: CET of P. limnophilus cells.
(a) Tomographic slice from a vitrified, cryo-thinned P. limnophilus sample showing the pole regions of three adjacent cells. A cell wall layer between the outer and inner membrane is visible in regions where the two membranes run parallel (arrowheads). The layer remains close to the outermost membrane where the inner membrane is invaginated (arrow). The reconstruction is binned three times and filtered. Scale bar, 200 nm. (b) Average of 1,059 subframes extracted from tomographic x–y slices along the cell envelope from non-polar regions where the inner membrane (bottom) runs approximately in parallel to the outer one (top). The inner membrane is only imperfectly aligned because of its varying distance to the outer membrane (also visible in a). The cell wall layer in between is clearly detectable (centre-to-centre distance to the outer membrane ≈22 nm). Contrary to the inner and outer membrane layers, which show high electron density, typically originating from phosphate in lipid head groups, the PG layer produces less contrast. Size of image 45 nm × 65 nm. (c) Segmentation of the reconstructed volume. Green: external membrane, cyan: internal membrane, red: PG layer, magenta: crateriform structures, violet: ribosomes, yellow: storage granules and white: holdfast substance.
