ISOLATION AND CHARACTERIZATION OF MORPHOLOGICAL VARIANTS OF ASPERGILLUS-PARASITICUS DEFICIENT IN SECONDARY METABOLITE PRODUCTION

Polyketide-producing Aspergillus parasiticus was developed as a model system to study fungal strain degeneration. One wild type and five spore colour and auxotrophic mutants of A. parasiticus (designated sec+ for secondary metabolism plus) making aflatoxin and/or pigmented pathway intermediates were subjected to a protocol of serial mycelial transfers in a defined medium. Variant forms (designated sec- for secondary metabolism minus) were isolated from the sec+ forms after 5-12 transfers. The sec- forms exhibited altered morphology, reduced sporulation and inability to make detectable levels of polyketide secondary metabolites. The variants were stable and did not revert to the parental characteristics after more than ten transfers. This pleiotrophic class of non-aflatoxigenic variants serves as a model system to study the commonly occurring, but poorly understood, phenomenon of strain degeneration in filamentous fungi.