Resistance to various inhibitors in Aspergillus nidulans.

Resistant strains of Aspergillus nidulans were obtained by one-step selection on high concentrations of various inhibitors; each strain was mutant in a different gene conferring resistance to actidione (Act), p-fluorophenylalanine (p f ) , teoquil ( te) , iodoacetate (Iod) or malachite green (mg). Some mutant alleles have been firmly, others tentatively, located. For comparative purposes attempts were made to find instances of multi-step or non-genic increases in resistance to malachite green and to teoquil, by prolonged exposure to low concentrations of inhibitor. No such increases were found. Iodl is fully dominant, Act1 is semidominant, pf21, t e l and rngl are recessive. mgl confers resistance to acriflavine to about the same degree as the non-allelic am 2 but these two mutant alleles do not show additivity. pf21 confers resistance to iodoacetate and also suppresses requirement for nicotinic acid (nic8). Iod I strains, which are not resistant to fluoroacetate, are able to use acetate as sole carbon source. Nutritionally balanced heterokaryons, between Act I and sensitive strains, show a gradual (and reversible) increase of the Act component on increasing actidione concentrations. Ultimately a plateau is reached ; this presumably represents the nutritional limits of each particular combination of nutritional markers.