Regulation of proline catabolism in Pseudomonas aeruginosa PAO

Mutants of Pseudomonas aeruginosa deficient in the utilization of L-proline as the only carbon and nitrogen source have been found to be defective either in proline dehydrogenase activity or in both proline dehydrogenase and delta 1-pyrroline-5-carboxylate dehydrogenase activities of the bifunctional proline degradative enzyme. The latter type of mutants was unable to utilize L-ornithine, indicating that a single delta 1-pyrroline-5-carboxylate dehydrogenase activity is involved in the degradation of ornithine and proline. Proline dehydrogenase and delta 1-pyrroline-5-carboxylate dehydrogenase activities were strongly and coordinately induced by proline. It was excluded that delta 1-pyrroline-5-carboxylate acted as an inducer of the bifunctional enzyme and it was shown that the low level induction observed during growth on ornithine was due to the intracellular formation of proline. The formation of the proline degradative enzyme was shown to be subject to catabolite repression by citrate and nitrogen control.