Development and Evaluation of a Potency Index Screen for Detecting Mutants of Penicillium chrysogenum Having Increased Penicillin Yield

Abstract

U.v.‐treated conidia of an industrial strain of Penicillium chrysogenum were spread on a growth‐limiting agar medium. Colonies arising from the survivors were surrounded with a spore suspension of Bacillus subtilis to which penicillinase had been added. After appropriate incubation, discrete zones of bacterial inhibition, with sizes limited by the penicillinase, appeared around each colony. Using the criterion of potency index (diameter of inhibition zone divided by diameter of colony) strains were selected that subsequently gave improved penicillin production in shake‐flasks. The technique also ranked correctly four industrial strains in order of their known penicillin‐producing capacity. Employing three operators, 5000 isolates could be screened in each experiment and approx. 15000 strains could be screened in a month.