FIG. 1.

Thin-section transmission electron microscopy of chemically fixed and dehydrated Corynebacterineae. (A) M. smegmatis mc²155. (B) C. glutamicum (CGL2020). The cell envelope of M. smegmatis is composed of a PM; a thick, electron-transparent layer (Peri ?; interpreted as the postulated periplasmic space); a thick, internal, electron-dense layer (EDL; considered a complex of peptidoglycan and arabinogalactan); a thin, electron-transparent layer (ETL; assumed to be composed of mycolic acids and other lipids); and an electron-dense OL (a complex protein-carbohydrate matrix with some lipids) (15, 16). The EDL and the mycolic acids of the ETL form the cell wall core. The cell envelope of C. glutamicum looks similar, but it does not possess an obvious low-density hypothetical periplasmic space and the OL is thicker than in M. smegmatis (43). In both cases, the use of ruthenium red stain resulted in enhanced staining of the OL. Bars, 20 nm.