Role of selective pressure by screening organisms in the development of producer mutant isolates of different antibiotic markers

The phenotypes of producer mutant isolates when obtained after mutagenesis of the spontaneous degenerate Aspergillus versicolor N₅ by screening on Trichophyton rubrum and those on A. niger G₃Br were found to be markedly different. In respect of phenotypic character anti- T. rubrum producer mutant isolates resembled the parental type more closely (which is specifically active against T. rubrum and generally against dermatophytes) than anti- A. niger mutant isolates. This clearly indicates not only the role of selective pressure of the screening organism in the development of a given producer mutant isolate but also shows the possibility of recovery of a producer type of the lost antibiotic marker.