T3SS complexes are reliably found in T3SS-expressing bacterial strains.

Cryo-tomograms were acquired from cryo-lamellae of various bacterial strains, with T3SS-like complexes identified exclusively in the tomograms of T3SS-encoding strains. Tomographic slices are shown (scale bars 200 nm) and when applicable T3SS regions are marked by a dashed box and corresponding insets shown (scale bars 50 nm). Z slices of tomograms and insets are indicated below the images. Vac.: Vacuole, OM: Outer membrane, IM: Inner membrane. (A) Shigella flexneri BS1276 (pWR100 deficient strain). No T3SSs were seen in tomograms. (B) WT Shigella flexneri M90T carrying the virulence plasmid pWR100, encoding for the T3SS structural component and most of the Shigella secreted effectors. Note that inset n°1 shows a gray area as the T3SS is on the edge of the tomogram. (C) E. coli mT3_Shigella, engineered E. coli strain expressing Shigella T3SS structural components including the translocon pore (IpaB, IpaC) and secreted effectors (IpaA, IcsB, IpgD).

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