FIG.4.

L. pneumophila morphology in late replicative phase. (A) SVir bacteria displaying an electron-dense cytoplasm and an outer membrane with sharp ripples, 25 h postinfection. Note that these morphologically distinct bacteria coexisted with bacteria displaying a standard gram-negative envelope and a less electron-dense cytoplasm. (B) Some bacteria (strain 2064 from a HeLa cell-grown inoculum is shown at 21 h postinfection) developed a rather straight (smooth) outer membrane. The envelope in these bacteria was often difficult to resolve. (C) In the 2064 strain, forms with sharp ripples could be seen at 12 h postinfection but also persisted until later times (D) (arrows), when they coexisted with the smooth-outer-membrane intermediates. (E) Late-replicating bacteria (SVir shown at 25 h postinfection) showed invaginations of the inner membrane (arrowheads). (F) Intricate replicative vacuole containing numerous SVir bacteria with some of the distinctive morphologies described for panels A to E is shown. Bars, 0.5 μm.