Certain factors which affect production and accumulation of indole-3- acetic acid (IAA) and activity of enzymes associated with its synthesis from L-tryptophan were investigated in Pseudomonas savastanoi. Addition of L- tryptophan to the culture medium enhances the accumulation of IAA by the bacterium. However, both tryptophan oxidative decarboxylase and indoleacetamide hydrolase, which are involved in the conversion of L-tryptophan to IAA, are produced by the bacterium without addition of L-tryptophan to the medium. In a medium containing L-tryptophan, yields of tryptophan oxidative decarboxylase per liter of culture suspension were increased as much as 2-fold.
IAA and indole-3-acetamide (IAM) strongly inhibit tryptophan oxidative decarboxylase. IAA up to 6×10^-3M did not inhibit indoleacetamide hydrolase. IAA also inhibits uptake of L-tryptophan by whole cells.
IAA is converted to its lysine conjugate by the bacterium. During logarithmic phase of growth in a nutrient medium, the specific activities of tryptophan oxidative decarboxylase and indoleacetamide hydrolase were 2-fold greater than that for the system converting IAA to its lysine conjugate. During the stationary growth phase, specific activity of all three enzymes decreased but that for the first two enzymes did so more rapidly than the specific activity of the lysine conjugate synthetase. Accumulation of IAA in culture filtrates is controlled to a large extent by the relative activities of the systems synthesizing and utilizing IAA.