Production ofl-Tryptophan by Mutants ofBrevibacterium flavumResistant to Both Tryptophan and Phenylalanine Analogues

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Abstract
5-Fluorotryptophan (5FT)-resistant mutants induced by one step mutation from a glutamate producing bacteria, Brevibacterium flavum No. 2247, accumulated only 0.4 g/liter of l-tryptophan at maximum. However, mutants resistant to higher concentrations of 5FT, which were further induced from the 5FT-resistant mutants, accumulated 1.4 to 2.4 g/liter of l-tryptophan. Their anthranilate synthetases of the tryptophan-specific pathway were less sensitive to the feedback inhibition by tryptophan than the parent enzymes and were not repressed by tryptophan. Moreover, the relationship between the l-tryptophan accumulation and the resistance of the enzymes to the feedback inhibition was parallel to a considerable extent. 3-Fluorophenylalanine (3FP)-resistant mutants induced from the 5FT-resistant mutants produced about twice as much l-tryptophan as the parental strains. Their l-tryptophan accumulation was not affected by the addition of excess l-phenylalanine and l-tyrosine, in contrast to that in the parents. Their 3-deoxy-d-arabino-heptulosonate-7-phosphate (DAHP) synthetases of the common pathway were insensitive to the synergistic inhibition by phenylalanine plus tyrosine. Since mutants resistant to 5FT and 3FP accumulated l-phenylalanine and l-tyrosine in addition to l-tryptophan, phenylalanine auxotrophs were induced, which produced 6.2 g/liter of l-tryptophan at maximum. The increment of the accumulation was almost equivalent to the amount of l-phenylalanine accumulated in the parental strain. These results were discussed on the basis of the regulatory mechanism for the aromatic amino acid biosynthesis in B. flavum.

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