A method for isolating an auxotrophic mutant from a wild-type culture of bacteria by adding penicillin to minimal medium. Penicillin interferes with cell wall development, causing growing wild-type cells to rupture. However, nongrowing auxotrophic mutant cells are not killed. After one hour, about 99% of the wildtype cells have lysed, releasing their pool of metabolites into the medium. The culture must be filtered to remove these metabolites, because the auxotrophic mutants would use them for growth and be subject to penicillin-induced lysis; the filtering also removes the penicillin. Alternatively, the enzyme penicillinase can be used to destroy the penicillin. Surviving auxotrophs are then supplied with enriched medium. These cells produce the colonies that are harvested. See Chronology, 1948, Lederberg and Zinder, Davis.
Subjects: Genetics and Genomics.