Naturally occurring variation in virulence in Aspergillus

Naturally-occurring variation in virulence was studied in the opportunistic fungal pathogens, Aspergillus nidulans and Aspergillus fumigatus. I measured variation in growth on Neiland’s solid agar medium and virulence in an insect model host, Galleria mellonella, in 92 A. nidulans recombinant strains generated by a cross between two wild type strains. A weak positive correlation was found between rate of growth and virulence. No difference in virulence was found between strains with pigmented and unpigmented conidia, even though conidial pigments are thought to be an important defence against the innate immune system. In 20 A. fumigatus wild type strains, isolates of the MAT 1-1 mating type were significantly more virulent in G. mellonella compared to MAT 1-2 mating type isolates. Surprisingly, environmental isolates were significantly more virulent than clinical isolates. My work provides the first step towards identifying the genes underlying virulence using quantitative trait locus mapping.