SUMMARY: A scries of phage-susceptible tryptophan-requiring mutants of , strain B, were found to fall into five distinct phenotypes as determined by their alternate growth response to anthranilic acid and indole, and by the substances which they accumulated in the culture fluids. An unidentified substance partially characterized by colorimetric reactions and absorption spectrum accumulated in the culture fluid of two of these types. Tryptophan-requiring T phage resistant mutants () which were readily obtained by phage selection could not be isolated by the penicillin method. This mutant represents a unique tryptophanless phenotype, not only in terms of its resistance to T phage, but also on the basis of: (1) accumulation of a new metabolic product; (2) growth stimulation by histidine and tyrosine; (3) suppression of accumulation of certain metabolic products by the other tryptophan auxotrophs; (4) epistatic expression of phenotype when superimposed on the tryptophan auxotrophs by secondary mutation.


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