FIG. 2.

Distinct structure encoded by the second pilus gene cluster. C. diphtheriae strain NCTC12139 (C to H) or its isogenic derivatives carrying deletion of specific genes [Δ(spaA) (A) and Δ(spaH) (B)] transformed with plasmid pSpaD carrying wild-type spaD (A, B, and F to H) or plasmid pSpaA carrying wild-type spaA (C to E) were immobilized on carbon grids, stained with specific antiserum α-SpaD (A, B, D, E, and F) or α-SpaA (C, G and H), and IgG-labeled with 12-nm (A to D and G to H) or 18-nm (E and F) gold-labeled IgG. Double-labeling experiments (E and H) were followed by staining cells with α-SpaA and 12-nm gold particles (E) or with α-SpaD and 18-nm gold particles (H). Samples were viewed by transmission electron microscopy. Arrows indicate structures of SpaA (opened) or SpaD (filled).