The Inheritance of Penicillin Titre in Wild-type Isolates of Aspergillus Nidulans

Abstract

S U M M A R YIn a sample of 52 wild-type isolates of Aspergillus nidulans, penicillin titre ranged from 0.0 to 14'4 units/ml. These differences in titre were under genetic control. Most of the variation between isolates was attributable to differences between heterokaryon-compatibility groups although significant differences were also found within groups. Genetic variation for penicillin titre was observed among the progeny in four of seven crosses between wild-type isolates. In these four crosses the variation was continuous, indicating that this is a polygenically determined character, and progeny with titres superior and inferior to those of the parents were produced. The genes determining penicillin production are predominantly additive in their action. Crosses between heterokaryon-incompatible isolates generated more genetic variation than those involving compatible parents, supporting the hypothesis that heterokaryon-compatible isolates are frequently closely related.

Genetics of Penicillin Titre in Lines of Aspergillus nidulans Selected through Recurrent Mutagenesis

“…nidulans has not been hampered by technical difficulties and has yielded clear results. However, it did not aim to provide information on the genetics of highly selected strains but concentrated on single major mutations affecting penicillin titre either positively (Ditchburn et al, 1976) or negatively ) and on natural variation in penicillin production (Holt & Macdonald, 19683;Merrick & Caten, 1975;Merrick, 1975a, …”

“…A more likely explanation is that some minor change in the fermentation conditions reduced the difference between the selected and unselected strains. Merrick (1975~) found that the difference in titre between natural high and low penicillin-producing isolates of A . nidulans was dependent on the batch of corn steep liquor used in the fermentation medium.…”

“…These analyses therefore confirm the segregation of alleles affecting penicillin titre in both backcrosses and indicate that these genetic differences must have been induced during the selection programmes since the ancestors A and B do not differ forIalleles affecting this character. Tests for non-additive gene effects were applied to the data for the two backcrosses as described by Caten (1975) andCaten (1979). In both crosses the progeny mean was significantly higher than the mid-parental value (A6-9 x B: [i] = -0.064, P = 0.01-0.001; B6-27xA: [i] = -0.170, P = <0-001) indicating non-additive gene action.…”

“…A l l sexual crosses were carried out by single perithecium analysis (Pontecorvo et al, 1953) following the procedure of Merrick & Caten (1975). Diploids were isolated from balanced heterokaryons by Roper's (1952) method.…”

Relationship of the Genetic Determination of Impaired Penicillin Production in Naturally Occurring Strains to that in Induced Mutants of Aspergillus nidulans

“…Variation in penicillin production among wild isolates of Aspergillus nidulans was first investigated by Holt & Macdonald (1968 a, b) and subsequently this character was shown to vary continuously under genetic control (Merrick & Caten, 1975). In both studies, however, it was apparent that a class of isolates existed which showed no detectable penicillin production.…”