An unstable strain of Aspergillus foetidus segregating proline auxotrophs

Two basic colony types have been obtained through single conidial isolation from the Bode strain of Aspergillus foetidus as well as from mutants of this unstable strain. Type I is prototrophic whereas type II is an auxotroph requiring proline. When a type I strain is grown on complex medium it gradually becomes overwhelmed by type II sectors of growth. However, essentially pure cultures of type I can be maintained on minimal medium (lacking proline). The yield of glucoamylase from type II cultures is less than half that obtained with type I cultures. The instability of type I cultures when grown on complex medium can not be explained by heterokaryosis or the presence of virus-like particles found in the original Bode strain and its derivatives. The isolation of five stable prototrophic strains obtained as more rapidly growing sectors from type I subcultures grown on complex medium suggests that the instability most probably results from a duplicated chromosomal segment or other chromosomal aberration analogous to those described in A. nidulans.