Cryo-electron tomography reveals OmpB is required for the Rickettsia parkeri S-layer

Many bacteria, and most archaea, have a paracrystalline protein surface layer (S-layer) encapsulating their outer membrane or cell wall. For pathogenic Rickettsia species, an S-layer has been hypothesized to be comprised of the outer membrane protein OmpB. We used cryo-electron tomography (cryoET) to image the Rickettsia parkeri cell surface and observed a repetitive S-layer structure proximal to the outer membrane of the bacterium that is absent in an ompB ^STOP ::tn mutant. Our data reveal that OmpB is essential for the Rickettsia S-layer and suggest that we can leverage cryoET to examine rickettsial S-layer structure and function.