Fig. 1.

Ring-shaped structures on the surface of L. pneumophila strain Lp01. Osmotically shocked L. pneumophila cells were mounted on discharged carbon grids and stained with 1% uranyl acetate. Transmission electron micrographs of a wild-type cell (A) and an isogenic deletion mutant (ΔT4SS) cell lacking all dot/icm genes (B) are shown. Large and small rings are denoted by large and small white arrowheads, respectively. (Scale bar, 200 nm.) (C) Large and small ring structures found on the wild-type L. pneumophila surface. (Scale bar, 40 nm.)