Divergent Targets of Aspergillus fumigatus AcuK and AcuM Transcription Factors during Growth In Vitro versus Invasive Disease

In Aspergillus nidulans, the AcuK and AcuM transcription factors form a complex that regulates gluconeogenesis. In Aspergillus fumigatus, AcuM governs gluconeogenesis and iron acquisition in vitro and virulence in immunosuppressed mice. However, the function of AcuK was previously unknown. Through in vitro studies, we found that A. fumigatus Delta acuK single and Delta acuK Delta acuM double mutants had impaired gluconeogenesis and iron acquisition, similar to the Delta acuM mutant. Also, the Delta acuK, Delta acuM, and Delta acuK Delta acuM mutants had similar virulence defects in mice. However, the Delta acuK mutant had a milder defect in extracellular siderophore activity and induction of epithelial cell damage in vitro than did the Delta acuM mutant. Moreover, overexpression of acuM in the Delta acuK mutant altered expression of 3 genes and partially restored growth under iron-limited conditions, suggesting that AcuM can govern some genes independently of AcuK. Although the Delta acuK and Delta acuM mutants had very similar transcriptional profiles in vitro, their transcriptional profiles during murine pulmonary infection differed both from their in vitro profiles and from each other. While AcuK and AcuM governed the expression of only a few iron-responsive genes in vivo, they influenced the expression of other virulence-related genes, such as hexA and dvrA. Therefore, in A. fumigatus, while AcuK and AcuM likely function as part of the same complex, they can also function independently of each other. Furthermore, AcuK and AcuM have different target genes in vivo than in vitro, suggesting that in vivo infection stimulates unique transcriptional regulatory pathways in A. fumigatus.