Control of pyrimidine synthesis in Pseudomonas fragi.

Abstract

To study the regulation of the de novo pyrimidine biosynthetic enzymes in the food-spoilage agent Pseudomonas fragi ATCC 4973. The de novo pyrimidine biosynthetic enzymes were measured in extracts of Ps. fragi ATCC 4973 cells and of cells from auxotrophs deficient for dihydroorotase or OMP decarboxylase activity. Pyrimidine biosynthetic enzyme activities in ATCC 4973 were influenced by pyrimidine supplementation to the culture medium. The pyrimidine limitation of each auxotroph elevated the de novo enzyme activities, indicating that this pathway may be repressible by a pyrimidine-related compound. Aspartate transcarbamoylase activity in ATCC 4973 was inhibited in vitro by pyrophosphate and purine or pyrimidine nucleotides. Pyrimidine synthesis in Ps. fragi appeared to be controlled at the transcriptional level and at the level of activity for aspartate transcarbamoylase. Its transcriptional regulation seemed to be more highly controlled than what was observed in the closely related species Pseudomonas putida and Pseudomonas fluorescens. This study demonstrates that pyrimidine synthesis is regulated in Ps. fragi. This could prove useful to future studies examining its biological control and its taxonomic assignment.