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Inducible System for the Utilization of ß-Glucosides in Escherichia coli II. Description of Mutant Types and Genetic Analysis

^a Department of Microbiology, New York University Medical Center, New York, New York

ABSTRACT

Two types of mutants obtained by treating ß-gl⁺ cells with nitrosoguanidine are described. One type, ß-gl⁺c, is constitutive for the biosynthesis of the aryl ß-glucoside splitting enzyme(s) and for the ß-glucoside permease; the other (ß-gl⁺sal^–) has lost the capacity to ferment salicin, but has retained the capacity to ferment arbutin and other aryl ß-glucosides. By two successive mutational steps, ß-gl⁺sal^–c double mutants can be obtained. Determinations of the enzymatic splitting of salicin and p-nitrophenyl ß-glucoside by ß-gl⁺sal^– cells and extracts showed that these mutants have lost the capacity to split salicin but do split p-nitrophenyl ß-glucoside; they possess the ß-glucoside permease, and in them salicin is a gratuitous inducer for enzyme and permease biosynthesis. Studies on a ß-gl⁺ strain, which splits salicin as well as p-nitrophenyl ß-glucoside, have shown that the splitting of salicin is more temperature-sensitive than that of p-nitrophenyl ß-glucoside and other ß-glucosides. Other properties of the two activities are similar. Interrupted mating experiments and cotransduction with P1kc phage showed that the genetic determinants of the ß-glucoside system map between the pyrE and ile loci. Three distinct mutational sites were found and are presumed to have the following functions: ß-glA, a structural gene for an aryl ß-glucoside splitting enzyme; ß-glB, either the structural gene for the ß-glucoside-permease or a regulatory gene; and ß-glC, a regulatory gene (or site). Escherichia coli wild-type strains are of the genotype A⁺ B^– C⁺. The ß-gl⁺ mutation determining the ability to ferment ß-glucosides is considered to be a permease or regulatory mutation, and the resulting genotype is A⁺ B⁺ C⁺. The ß-gl⁺sal^– phenotype results from a mutation in the ß-glA gene (genotype A' B⁺ C⁺), and the constitutive phenotype results from a mutation in the ß-glC gene, the genotypes A⁺ B⁺C_a and A' B⁺C_a corresponding to the phenotypes ß-gl⁺c and ß-gl⁺sal^–c.

¹ Present address: Department of Microbiology, New York University College of Dentistry, New York, N.Y.

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