The Isolation of Biochemically Deficient Mutants of Bacteria by Means of Penicillin

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Abstract
A method is descr. for the isolation of biochemically deficient mutants of bacteria. This procedure is based on the fact that penicillin sterilizes only growing bacteria; mutants selectively survive exposure to penicillin in a minimal medium which is inadequate for their nutrition. By this technique a large variety of mutants of Escherichia coli have been obtained with requirements for amino acids, nucleic acid components, and vitamins. Mutants induced by u.-v. irradiation do not survive exposure to penicillin in minimal medium unless they are first permitted a period of growth, during which the new genotype achieves physiologic expression as a deficient phenotype. The term "phenome" is proposed to denote the total extragenic material of the cell, and the term "phenomic lag" to describe the delay in phenotypic expression. Syntrophism also contributes to the susceptibility of mutants to penicillin in minimal medium.

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