Aspergillus fumigatusis a ubiquitous fungus that is a frequent opportunistic pathogen in immunosuppressed patients. Because of its role as a pathogen, it is of considerable experimental interest. A set of auxotrophic isogenic strains in theA. fumigatusgenome reference strain AF293 has been developed. Using molecular genetic methods, arginine and lysine auxotrophs were made by deletion ofargBandlysB, respectively. Transformation of these auxotrophic strains with plasmids carryingargBorlysB, respectively, results in efficient integration at these loci. Finally, these strains are able to form stable diploids, which should further facilitate analysis of gene functions in this fungus. Furthermore, the development of this isogenic set of auxotrophic strains in the AF293 background will enable investigators to study this important opportunistic human pathogen with greater facility. [ABSTRACT FROM AUTHOR]