A major cell wall component : alpha1,3 glucans represent 40 % of the cell wall polysaccharides in Aspergillus fumigatus. They are recovered in the alkali-soluble fraction of the cell wall. Chemical analysis have shown that cell wall alpha1,3 glucans are composed of linear chains with episodic intrachains of alpha1,4 linked glucose. The cell wall of the mycelium developped in static aerial (StA) or shaken immerged (ShI) conditions, differs in composition and localization of some polysaccharides. alpha1,3 glucans are present in similar amount in StA or ShI cell wall but they are localized exclusively in a thick layer at the surface of the StA cell wall whereas a thin layer of alpha1,3 glucans and an intermediate layer were observed in the ShI cell wall. A glue sticking together A. fumigatus aerial hyphae in a biofilm structure : an hydrophobic strong, non-dissociable network of hyphae is formed in the StA condition whereas the ShI condition allow the development of dispersed hydrophilic hyphae. The aerial network of hyphae (StA) was fused by an extracellular amorphous matrix which also covers the mycelial mat like in bacterial or yeast biofilms. The analysis of the extracellular matrix shows that one major component of this extracellular matrix is the alpha1,3glucans. An anchor for melanin : alpha1,3glucans are also present in the cell wall of the conidia of A. fumigatus. They are mostly localized at the cell wall surface where they colocalize with the melanin layer. Three putative alpha1,3glucans synthase genes AGS1, AGS2 and AGS3 have been identified. The gene deletion of AGS1 only results in a partial reduction of the alpha1,3 glucan concentration in the cell wall. Deletion in AGS1 or AGS2 are not defective in virulence. In contrast, AGS3 can modulate the virulence of A. fumigatus. An AGS3 deletion strain was found to produce conidia more resistant to H2O2 than the parental strain. The ags3 mutant causes more rapid and progressive disease in a mice model than the wild type. The apparent hyper-virulence was correlated with an increased melanin content of the conidial cell wall.
Full conference title:
The First International Fungal / Plant Cell Wall Meeting
- International Fungal / Plant Cell Wall Meeting 1st