Nitrogen Control in Pseudomonas aeruginosa: Mutants Affected in the Synthesis of Glutamine Synthetase, Urease, and NADP-Dependent Glutamate Dehydrogenase

Mutants were isolated from Pseudomonas aeruginosa that were impaired in the utilization of a number of nitrogen sources. In contrast to the wild-type strain, these mutants appeared to be unable to derepress the formation of glutamine synthetase and urease under nitrogen-limited growth conditions, whereas NADP-dependent glutamate dehydrogenase became derepressed. This GlnR- phenotype appeared to be caused by a mutation located in the early region of the P. aeruginosa PAO chromosomal map, close to hisIV59. Partial suppression of the GlnR- phenotype due to a mutation located close to hisII4 was observed. These revertants were different from both the wild-type strain and the GlnR- mutant with respect to the regulation of the synthesis of glutamine synthetase, urease, and NADP-dependent glutamate dehydrogenase (GlnRc phenotype). Also the regulation of glutamine synthetase activity by adenylylation/deadenylylation was altered in the revertants. The results suggest the presence of a regulatory gene that plays a role in the regulation of enzyme formation in response to the availability of ammonia.