Ultrastructure of the cell envelope layers and surface details of Legionella pneumophila.

Ten strains representing six serogroups of Legionella pneumophila were examined by electron microscopy using freeze-etching, thin-sectioning and negative-staining techniques. In addition, selected strains were examined further as shadowed and freeze-dried preparations and by scanning electron microscopy. The cell envelope consisted of two membranes, evident in fractured specimens as four short ridges. The major fracture plane was through the inner membrane, and therefore the protoplasmic and extracellular fracture faces of this membrane were predominant. With the exception of one strain (Togus 1), the particle arrangement on these fracture faces was random. A peptidoglycan-like cell wall layer was revealed only in sections of partially plasmolysed cells. Membrane-bounded poly-beta-hydroxybutyrate-like granules were evident in the cytoplasm and these frequently showed plastic deformation due to fracturing. Although appendages were present, the surfaces of organisms and of isolated cell membranes showed no regular arrays of particles.