Selection of multiple disruption events in Aspergillus fumigatus using the orotidine-5'-decarboxylase gene, pyrG, as a unique transformation marker.

A 8.6-kb disruption cassette, referred to here as a pyrG-blaster and consisting of the Aspergillus niger pyrG gene flanked by a direct repeat that encodes the neomycin phosphotransferase of transposon Tn5 was constructed. Following transformation of a uridine/uracil auxotrophic pyrG strain of A. fumigatus, genomic insertions of the pyrG-blaster were obtained either by targeted gene replacement at the rodA locus, resulting in the formation of hydrophilic spores, or by ectopic integration. In both cases, recombination between the two elements of the direct repeat could be selected in the presence of 5-fluoro-orotic acid and resulted in the excision of the A. niger pyrG gene, producing A. fumigatus uridine/uracil auxotrophs that retained their additional mutant phenotype because of the persistence of one of the two elements of the direct repeat at the site of insertion of the pyrG-blaster. Selection for uracil/uridine prototrophy can therefore be used again to disrupt another gene.