Biosynthesis of histidine, arginine, riboflavin and pantothenic acid, but not siroheme, is crucial for virulence of Aspergillus fumigatus

Aspergillus fumigatus is the most prevalent airborne fungal pathogen causing invasive fungal infections in immunosuppressed individuals. Limitations in antifungal therapy arise from non-specific symptoms of infection, poor diagnostics and comparatively few options for treatment. The aim of this study is to explore the metabolism of A. fumigatus on a comprehensive scale as essential virulence determinant to generate a collection of A. fumigatus strains with a focus on primary metabolism to target fungal pathways that are absent in mammals. Based on the annotated genome of A. fumigatus, metabolic network reconstruction served to identify fungal-specific pathways and key reactions. Predictions for unique enzymes resulted in a candidate list of genes, the inactivation of which is likely to result in an auxotrophic phenotype. The virulence potential of the generated auxotrophic mutant strains was then analyzed in various host niches. We identified five A. fumigatus pathways that are essential for growth in minimal medium: biosynthesis of the amino acids histidine and arginine, the vitamins riboflavin and pantothenic acid, and the heme-like prosthetic group siroheme, which is essential for sulfate and nitrate assimilation as well as nitric oxide detoxification. Inactivation of biosynthesis of histidine, arginine, riboflavin and pantothenic acid, but not siroheme, resulted in attenuated virulence of A. fumigatus in murine models for invasive aspergillosis with intranasal and systemic infection. The results characterize the availability of nutrients in the host niche and reveal targets for development of novel antifungal therapeutic approaches.