Metabolism of Tryptophan by Pseudomonas aureofaciens and Its Relationship to Pyrrolnitrin Biosynthesis

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Abstract
Studies on the metabolism of tryptophan in P. aureofaciens ATCC 15926 revealed different metabolic routes for the L- and D-isomer besides the biosynthetic pathway for pyrrolnitrin [an antifungal agent] synthesis. L-Tryptophan catabolism follows the aromatic route via anthranilic acid. Tryptophan 2,3-dioxygenase was induced by L-tryptophan. Kynureninase and anthranilate 1,2-dioxygenase were induced by L-tryptophan, L-kynurenine and anthranilic acid. Anthranilate 1,2-dioxygenase was absent from a mutant strain of P. aureofaciens ATCC 15926 which produced about 30-fold increased amounts of pyrrolnitrin. The Km values of tryptophan 2,3-dioxygenase and kynureninase did not differ substantially between the 2 strains. Kynurenine 3-monooxygenase, 3-hydroxyanthranilate 3,4-dioxygenase, tryptophanase and indolyl-3-alkane .alpha.-hydroxylase activities were not detected. D- and L-tryptophan were converted to indole-3-pyruvate by tryptophan aminotransferase and via indole-3-acetaldehyde to indole-3-acetic acid. This additional catabolic pathway and tryptophan racemase activity were constitutive and present in both strains.