Pyrimidine nucleotide synthesis in Pseudomonas nitroreducens and the regulatory role of pyrimidines

Control of pyrimidine biosynthesis in the commercially important, hydrocarbon-utilizing bacterium Pseudomonas nitroreducens ATCC 33634 was investigated. When glucose-grown wild-type cells were supplemented with uracil or orotic acid, the pyrimidine biosynthetic activities were depressed. Pyrimidine limitation of glucose-grown cells of an orotate phosphoribosyltransferase mutant caused aspartate transcarbamoylase and dihydroorotase activities to increase by about 4-fold while the other enzyme activities about doubled. In succinate-grown phosphoribosyltransferase mutant cells subjected to pyrimidine limitation, transcarbamoylase and dehydrogenase activities rose by about 5-fold while dihydroorotase activity more than tripled. In an OMP decarboxylase mutant, pyrimidine limitation of glucose-grown cells increased transcarbamoylase, dihydroorotase, dehydrogenase and phosphoribosyltransferase activities by 4-, 10-, 6- and 3.8-fold, respectively. Pyrimidine limitation of the succinate-grown decarboxylase mutant cells increased aspartate transcarbamoylase or dihydroorotase by more than 4-fold and the other activities by about 2-fold. Pyrimidine biosynthetic enzyme synthesis appeared to be regulated by pyrimidines with the regulation being influenced by the carbon source present. Aspartate transcarbamoylase activity in Ps. nitroreducens was regulated at the level of enzyme activity since the enzyme was strongly inhibited by UDP, pyrophosphate, ATP and ADP. Overall, the regulation of pyrimidine biosynthesis in Ps. nitroreducens can be used to differentiate it from other taxonomically related species of Pseudomonas.