Loss of chloramphenicol production in strains of Streptomyces species 3022a treated with acriflavine and ethidium bromide

An assay procedure was developed to detect chloramphenicol production in large numbers of Streptomyces species 3022alpha isolates, and was used to screen colonies from cultures exposed to acriflavine and ethidium bromide. There was a significant rise in the proportion of low- and non-producing strains in the treated cultures. Since the organism developed resistance to acriflavine but not ethidium bromide, the effects of the latter agent were examined in more detail. Loss of chloramphenicol production was not due to mutation, nor to differential sensitivity to the drug among producing and non-producing natural variants. The response of cultures varied with age, and at least three strain types--high-, low-, and non-producers could be distinguished. A study in shaken cultures of selected isolates from the screening process established the general reliability of the screening method and showed that the assay probably sometimes failed to distinguish between low- (15-20 mg/iota) and non-producers. It indicated that the non-producer class consisted of some very low (up to 4 mg/iota) producers as well as fully negative strains, and it confirmed indications from the screening results that a non-producing isolate obtained by acriflavine treatment accumulated aromatic amines and was probably blocked in the pathway for chloramphenicol biosynthesis.