Aspergillus fumigatus encounters low oxygen microenvironments during infection. Adaptation to low oxygen microenvironments is essential for virulence and is transcriptionally regulated by the sterol regulatory binding proteins, SrbA and SrbB. Additionally, A. fumigatus grows in a biofilm-like structure in vivo and this phenotype requires SrbA for full biofilm formation. To identify metabolic genes important within the infection environment and for biofilm formation, we identified genes with increased expression in low oxygen conditions. An alanine aminotransferase, alaA, was found to be one of the few amino acid metabolism genes that was both directly regulated by SrbA, as determined by ChiP-seq, and had increased mRNA levels in low oxygen. To determine how alanine metabolism via alaA affects fungal biology and virulence, alaA null mutants were generated in 2 different A. fumigatus strains, CEA10 and Af293. alaA null mutants are not auxotrophic and were capable of catabolizing alanine as a sole carbon or nitrogen source. Loss of alaA resulted in a moderate decrease in growth under biofilm-forming conditions that was independent of oxygen levels. This growth decrease was found to be largely attributable to a germination delay that is rescued by supplementation with yeast extract, but not alanine or any other nitrogen sources tested. Intriguingly, loss of alaA results in decreased expression of galactosaminogalactan biosynthetic genes and a concomitant decrease in adherence to abiotic surfaces. Histological data from a murine invasive aspergillosis model suggests that alaA is involved in germination and growth within the murine lung, and qPCR analysis indicate that loss of alaA results in a reduced fungal burden. Taken together, these data reveal that alanine metabolism via alaA plays a significant role in A. fumigatus’ ability to germinate, adhere to surfaces, and grow within the murine lung.
Full conference title:
- Fungal Genetics Conference 30th (2019)