Antimycin A fermentation. I. Production and selection of strains.

Increase in antimycin A production was achieved through a parallel strain and medium improvement program: a 125-fold augmentation (75 to 9,500 mug/ml) was obtained. The selective system included antimycin A productivity, conidiation, sensitivity to ultraviolet radiation, growth rate and yield, and absence of pigment and actinomycin D production. Among the original strains tested one natural isolate possessed high productivity and several of the above characteristics, and was selected for mutagenesis. Spontaneous and induced variability was then exploited in isolating high-producing strains. The first mutagen used was ultraviolet radiation; it was replaced by ethylenimine when it became no longer efficient in increasing variability. As new, high producers were isolated, the medium was modified to best suit their requirements for still higher productivity. The critical environmental factors were absence of phosphate and organic salts, concentration of the nitrogen source and ratio organic/inorganic nitrogen, ratio ammonium sulfate/calcium carbonate, and addition of slowly utilizable carbon sources, such as lactose and oil; optimum temperature and initial pH were 25 degrees C and 7.0. Aeration/agitation requirements of improved strains were high. Fermentation was characterized by abrupt pH changes which impaired rapid accumulation of the antibiotic. Antimycin A was produced during both the trophophase and idiophase.