Production of L-Tryptophan by Sulfonamide-resistant Mutants

Sulfaguanidine-resistant mutant S-225, derived from a tryptophan-producing 5-fluoro-tryptophan-resistant mutant of Brevibacterium flavum, accumulated 19 g/liter of L-tryptophan at maximum when cultured for 72 hr in a medium containing 13% glucose as carbon source, 1.8-fold higher than did the parent. Strain S-225 accumulated 17 g/liter of L-tryptophan in a medium containing 10% sucrose as carbon source (17% yield based on the sugar). It also accumulated 450 mg/liter of chorismate, an intermediate common to the biosyntheses of tryptophan and p-aminobenzoate. The accumulation was 1.7-fold higher than that by the parent, suggesting that the intracellular concentration of chorismate was increased through acquisition of the sulfaguanidine resistance. Sulfaguanidine-resistant mutants were also derived from a tryptophan-producing mutant of Corynebacterium glutamicum. The mutants showed 2.2-fold higher maximum tryptophan production than did the parent.