AGS3, an alpha(1-3)glucan synthase gene family member of Aspergillus fumigatus, modulates mycelium growth in the lung of experimentally infected mice.

The cell wall of human fungal pathogen Aspergillus fumigatus protects the fungus against threats from environment and interacts with the host immune system. Alpha(1-3)glucan is the major polysaccharide of Aspergillus fumigatus cell wall, and it has been shown to contribute to the virulence of diverse fungal pathogens. In A. fumigatus, three putative alpha(1-3)glucan synthase genes AGS1, AGS2 and AGS3 have been identified. AGS1 is responsible for cell wall alpha(1-3)glucan biosynthesis, but strains with deletions of either AGS1 or AGS2 are not defective in virulence [Beauvais, A., Maubon, D., Park, S., Morelle, W., Tanguy, M., Huerre, M., Perlin, D.S., Latgé, J. P., 2005. Two alpha(1-3) glucan synthases with different functions in Aspergillus fumigatus. Appl. Environ. Microbiol. 71, 1531-1538]. In contrast, we present evidence that AGS3 is also responsible for cell wall alpha(1-3)glucan biosynthesis and can modulate the virulence of A. fumigatus. An AGS3 deletion strain was found to produce faster and more robust disease than the parental strain in an experimental mouse model of aspergillosis. The apparent hyper-virulence in the AGS3-deleted mutant was correlated with an increased melanin content of the conidial cell wall, a better resistance to reactive oxygen species and a quicker germination rate. These results suggest an indirect role for AGS3 in virulence through an adaptive mechanism.