Evolution of Aspergillus niger and A-nidulans in glucose-limited chemostatcultures, as indicated by oscillations in the frequency of cycloheximide resistant and morphological mutants

Aspergillus niger and A. nidulans were grown separately in glucose-limited chemostat cultures on modified Vogel's medium. Periodic selection (the appe arance of new mutant populations) in A. niger was determined by monitoring oscillations in the concentration of cycloheximide-resist ant mycelial frag ments in samples from the fermenter vessel. Using these data, the interval between the periodic selection of each new mutant population was 32+/-6 gen erations (mean+/-S.E.M.). Periodic selection in cycloheximide resistance in three morphologically distinct sub-populations of the A. niger culture ave raged 36+/-2, 31+/-11 and 28+/-5 generations and these values were not sign ificantly different from that of the whole population (32+/-6 generations). Also, it was possible to estimate the rate of evolution taking place in th ese cultures by monitoring oscillations in the frequency of morphological m utants. The intervals between the periodic selection of morphological mutan t populations in A. niger and A. nidulans were 28+/-3 and 22+/-2 generation s respectively.