Characterizing the pathogenic, genomic, and chemical traits ofAspergillus fischeri, a close relative of the major human fungal pathogenAspergillus fumigatus
Authors: Mead Matthew E. , Knowles Sonja L. , Raja Huzefa A. , Beattie Sarah R. , Kowalski Caitlin H. , Steenwyk Jacob L. , Silva Lilian P. , Chiaratto Jessica , Ries Laure N.A. , Goldman Gustavo H. , Cramer Robert A. , Oberlies Nicholas H. , Rokas Antonis 
Published: September 2018

Aspergillus fischeriis closely related toAspergillus fumigatus, the major cause of invasive mold infections. Even thoughA. fischeriis commonly found in diverse environments, including hospitals, it rarely causes invasive disease; why that is so is unclear. Comparison ofA. fischeriandA. fumigatusfor diverse pathogenic, genomic, and secondary metabolic traits revealed multiple differences for pathogenesis-related phenotypes, including thatA. fischeriis less virulent thanA. fumigatusin multiple animal models of disease, grows slower in low oxygen environments, and is more sensitive to oxidative stress. In contrast, the two species exhibit high genomic similarity; ~90% of theA. fumigatusproteome is conserved inA. fischeri, including 48/49 genes known to be involved inA. fumigatusvirulence. However, only 10/33A. fumigatusbiosynthetic gene clusters (BGCs) likely involved in secondary metabolite production are conserved inA. fischeriand only 13/48A. fischeriBGCs are conserved inA. fumigatus. Detailed chemical characterization ofA. fischericultures grown on multiple substrates identified multiple secondary metabolites, including two new compounds and one never before isolated as a natural product. Interestingly, anA. fischerideletion mutant oflaeA, a master regulator of secondary metabolism, produced fewer secondary metabolites and in lower quantities, suggesting that regulation of secondary metabolism is at least partially conserved. These results suggest that the non-pathogenicA. fischeripossesses many of the genes important forA. fumigatuspathogenicity but is divergent with respect to its ability to thrive under host-relevant conditions and its secondary metabolism.

Importance

Aspergillus fumigatusis the primary cause of aspergillosis, a devastating ensemble of diseases associated with severe morbidity and mortality worldwide.A. fischeriis a close relative ofA. fumigatus, but is not generally observed to cause human disease. To gain insights into the underlying causes of this remarkable difference in pathogenicity, we compared two representative strains (one from each species) for a range of host-relevant biological and chemical characteristics. We found that disease progression in multipleA. fischerimouse models was slower and caused less mortality thanA. fumigatus. The two species also exhibited different growth profiles when placed in a range of stress-inducing conditions encountered during infection, such as low levels of oxygen and the presence of reactive oxygen species-inducing agents. Interestingly, we also found that the vast majority ofA. fumigatusgenes known to be involved in virulence are conserved inA. fischeri, whereas the two species differ significantly in their secondary metabolic pathways. These similarities and differences that we identified are the first step toward understanding the evolutionary origin of a major fungal pathogen.