Tallysomycin-induced mitotic aneuploidy and point mutations in Aspergillus nidulans.

Tallysomycin is an antibiotic compound structurally related to bleomycin, and like bleomycins and phleomycins also shows antitumour activity. We have investigated the genetic activity of tallysomycin in the ascomycete Aspergillus nidulans for malsegregation of chromosomes at mitosis and for point mutations. We found that the antibiotic at very low concentrations from 0.025 to 0.2 micrograms/ml had an inhibitory effect on colonial growth of up to 50% and it increased the number of mitotic malsegregants from 311% to 607% over the control value. Tallysomycin at concentrations between 2 and 16 micrograms/ml (which inhibited the germination of conidia from 30 to 90%) also increased the number of methionine suppressor revertants from 59 to 368 per 10(6) conidia. With regard to the mechanism for induced mitotic segregation it was shown that this may involve non-disjunction of chromosomes which through the intermediate formation of unstable aneuploids resulted in formation of stable haploid and diploid segregants.