Direct Visualization by Cryo-EM of the Mycobacterial Capsular Layer: A Labile Structure Containing ESX-1-Secreted Proteins (original) (raw)
Figure 1
Visualization of the capsule in its native state.
Cryo electron micrographs of intact S. flexneri cell plunge frozen (A) depicts the typical cell envelope profile using this method of sample preparation. (B) M. smegmatis cells grown with both chemical and mechanical perturbation shows a cell envelope with morphology similar to S. flexneri. Similar cells cultured in an unperturbed state before freezing (C) shows the presence of an extra layer (bracket) surrounding the mycomembrane. Corresponding layers are also observed surrounding the mycomembranes of M. tuberculosis (D), M. marinum (E), and M. bovis BCG (F). The density profiles in B' and C' were obtained from images corresponding to B and C respectively. Images were averaged over a width of 75 pixels. The outermost layer varies in thickness from negligible to considerable (40 nm; see Table S1) indicating the unstable nature of this layer. Arrow heads point to plasma membrane (PM; magenta) and outer membrane/mycomembrane (MOM; blue). Scale bars: 100 nm.