Production of L-Tryptophan by Mutants of Brevibacterium flavum Resistant to Both Tryptophan and Phenylalanine Analogues

Abstract

5-Fluorotryptophan (5 FT^*) -resistant mutants induced by one step mutation from a glutamate producing bacteria, Brevibacterium flavum No. 2247, accumulated only 0.4g/liter of L-tryptophan at maximum. However, mutants resistant to higher concentrations of 5 FT, which were further induced from the 5 FT-resistant mutants, accumulated 1.4 to 2.4g/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 (3 FP) -resistant mutants induced from the 5 FT-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. Their3-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 5 FT and 3 FP accumulated L-phenylalanine and L-tyrosine in addition to L-tryptophan, phenylalanine auxotrophs were induced, which produced 6.2g/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.