Cell wall structure. Cell wall structure. (A) Transmission electron micrograph of a section of a C. albicans cell prepared by freeze-substitution, showing the cell wall as a thick, electron-dense, homogeneous structure. The presence of distinct layers was not evident in this preparation. Bar, 1 μm. Reprinted from reference3 with permission of the publisher. (B) Thin sections of cells treated with gold-conjugated concanavalin A, showing an intense labeling with gold particles of the external wall surface. The surface exhibits a fibrillar appearance (arrows), suggesting that concanavalin A-reactive cell wall components, i.e., mannoproteins, are particularly abundant at the most external wall layers. The remaining wall structure also appeared as a homogenous structure in this transmission electron micrograph. Bar, 0.5 μm. Reprinted from reference 549 with permission of the American Society for Microbiology. (C) Other procedures for transmission electron microscopy examination of thin sections of C. albicans cells revealed more clearly the presence of an outer floccular layer (arrow) and showed that the remaining cell wall structure is not homogeneous and that some layering exists. Bar, 200 nm. Reprinted from reference 240 with permission of the publisher. (D to F) Complexity of the wall ultrastructure and presence of distinct layers in the cell wall of C. albicansas revealed by different scanning electron microscopy-based procedures such as cryo-scanning electron microscopy (D) and freeze-fracture, freeze-etch analysis (E and F). The presence of well-ordered, regularly arranged, radiating fibrils in the outer layer is particularly evident in the micrographs shown in panels E (hydrophilic cells) and F (hydrophobic cells). Bar, 0.3 μm in both panels. Panel D reprinted from reference 246 with permission of the publisher. Panels E and F reprinted from reference 191 with permission of the publisher. W. Lajean Chaffin et al. Microbiol. Mol. Biol. Rev. 1998; doi: