- Pseudomonas aureo/aciens does not excrete phenazine-a-carboxylic acid, either in a medium with pyruvic acid as sole source of carbon or in a medium with glutamic acid as sole source of carbon, but pigmentation will occur in a medium with glutamic acid -4-pyruvic acid as carbon sources. 2. Each of these carbon sources does give rise to phenazine-a-carboxylic acid synthesis in a medium supplemented with 1 mYi of the three aromatic amino acids. 3. A mutant strain of Pseudomonas/luorescens var. pseudoiodinum excretes protocatechuic acid and gallic acid in media with pyruvic acid ~-glutamic acid as carbon sources, but not or very scarcely in media with only one of these two organic acids as sole source of carbon. 4. When supplemented with the three aromatic amino acids, non of the hydroxybenzoic acids could be found in this medimn inoculated with this strain.
It appears, that the surplus of the aromatic biosynthesis in P. aureo/aciens is channeled into phenazine-a-carboxylic acid formation, whereas in P./luorescens var. pseudoiodinum the enzymes of this pathway are inhibited or repressed if the media are supplemented with the aromatic amino acids.