FIG. 1.

Identification of the second pilus of Corynebacterium diphtheriae. C. diphtheriae strain NCTC12139 (A) or its isogenic derivatives with a deletion of the spaD gene [ΔspaD (B)] transformed with plasmid pSpaD encoding wild-type spaD (C to F) were immobilized on carbon grids and stained with a specific antiserum. Single-labeling experiments were carried out by staining cells with α-SpaD (A to C, E, and F) or α-SpaE (D) and IgG-labeled 12 nm (A to D) or 6 nm (E and F) gold particles. In double-labeling experiments (E and F) α-SpaD/IgG-6-nm gold-stained cells were then stained with α-SpaE (E) or α-SpaF (F) and 12-nm gold-labeled IgG. Labeled SpaE pilins (open arrows) are spotted along the SpaD fibers (E). Few labeled SpaF pilins (arrows) are found at the pilus tip (F). Samples were viewed by transmission electron microscopy. Bars indicate a distance of 0.2 μm.