Architecture and chemistry of microconidial walls of Trichophyton mentagrophytes

Abstract

The ultrastructure and chemical composition of the walls of T. mentagrophytes microconidia were investigated with particular emphasis on the localization of the major structural components within the walls. The walls consisted of carbohydrate (56.1% neutral polysaccharide, and 16.0% chitin), protein (22.6%), lipid (6.5%), ash (1.7%) and trace amounts of melanin (0.2%) and phosphorus (0.2%). In thin sections, 3 distinct layers were recognized. The electron-transparent pellicle (15-20 nm thick) covering the outermost surface of the wall consisted of a glycoprotein-lipid complex and was mostly extracted by sodium phosphate buffer (0.1 M, pH 6.5) containing 8 M urea, 1% (vol/vol) mercaptoethanol and 1% (wt/vol) sodium dodecyl sulfate. The middle electron-dense layer (30-50 nm thick) represented the proteinaceous rodlet layer embedded in polysaccharides and was completely solubilized by hot alkali extraction (1 N NaOH, 100.degree. C, 1 h). The thick inner layer (200-300 nm thick) was relatively resistant to the above treatments and was found to consist of amorphous glucans and microfibrillar chitin. Approximately half of the inner wall glucans was susceptible to (1 .fwdarw. 3)-.beta.-glucanase.