Resistance to various Inhibitors in Aspergillus nidulans

Abstract

Resistant strains of Aspergillus nidulans were obtained by 1-step selection on high concentrations of various inhibitors; each strain was mutant in a different gene conferring resistance to actidione (Act), p-fluoro-phenylalanine (pf), 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. Iod 1 is fully dominant, Act 1 is semi-dominant, pf 21, te 1 and mg 1 are recessive, mg 1 confers resistance to acriflavine to about the same degree as the non-allelic acr 2 but these 2 mutant alleles do not show additivity. pf 21 confers resistance to iodoacetate and also suppresses requirement for nicotinic acid (nic 8). Iod 1 strains, which are not resistant to fluoroacetate, are able to use acetate as sole carbon source. Nutritionally balanced heterokaryons, between Act 1 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.