Signature-tagged and directed mutagenesis identify PABA synthetase as essential for Aspergillus fumigatus pathogenicity

Signature-tagged mutagenesis (STM) is a method that has been used to screen for genes required for in vivo survival of pathogenic bacteria, but has no t been used to investigate a eukaryotic pathogen in an animal model of dise ase. We have adapted STM to identify genes required for in vivo growth of t he opportunistic fungal pathogen Aspergillus fumigatus. Using a mouse model of invasive pulmonary aspergillosis, we have isolated several mutant strai ns with defects in their ability to replicate in vivo. One strain unable to cause lethal infection was further characterized and found to have an inse rtion into the promoter of a gene (pabaA) encoding para-aminobenzoic acid s ynthetase, an enzyme catalyzing a late step in the biosynthesis of folate. The complete inability of this strain, and other pabaA(-) strains construct ed in this study by targeted gene deletion, to cause lethal infection in mi ce confirms the importance of the folate synthesis pathway for in vivo surv ival of this pathogen. The successful application of STM to A. fumigatus de monstrates that in vivo genetic analysis of eukaryotic pathogens is feasibl e and could result in the identification of potential targets, such as para -aminobenzoic acid synthetase, for novel antifungal therapies.