Production of Tryptophan by Salmonella typhi and Escherichia coli

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Abstract
Microbiological assays of the extracts of S. typhi bacteria indicated the presence of a material with the biological activity of tryptophan. E. coli mutants were utilized for two types of experiments. When a culture of a tryptophan-requiring coli mutant and a typhoid strain were mixed, syntrophic growth was seen. In a second series of experiments the E. coli mutant was used as a lawn. Various strains of S. typhi were tested for tryptophan production by observation of zones of growth on the lawn. One strain which failed to grow under these conditions would do so in an atmosphere of indole, which acts as substrate of the synthetic enzyme and causes larger quantities of tryptophan to be produced. E. coli cultures also show an increase in tryptophan when grown in an atmosphere of indole; here indole acts as an inhibitor of tryptophanase, allowing the tryptophan produced to survive.