Pyrimidine Nucleotide Biosynthesis and Regulation in Pseudomonas lemonnieri.

The pyrimidine biosynthetic pathway regulation in the bacterium Pseudomonas lemonnieri ATCC 12983 was investigated since this strain synthesizes a blue aromatic pigment that could have a commercial application as a dye. The effect of the pyrimidine bases, orotic acid and uracil metabolites, on the enzymes unique to the pyrimidine biosynthetic pathway was studied. It was found that pyrimidine addition to the medium affected the biosynthetic enzymes differently depending on the carbon source present. Using chemical mutagenesis and 5-fluoroorotic acid resistance, a mutant strain deficient for OMP decarboxylase activity was isolated. The uracil-requiring mutant strain could also utilize cytosine, uridine, or uridine monophosphate as a pyrimidine source. When the mutant strain was limited for pyrimidines for 1 or 2 h, derepression of pyrimidine biosynthetic enzyme activities was observed in the glucose-grown cells but not in the succinate-grown cells. Clearly, carbon source was a factor in the regulation of pyrimidine biosynthesis in P. lemonierri. The regulation of the known regulatory pyrimidine biosynthetic enzyme aspartate transcarbamoylase activity was examined in succinate-grown ATCC 12983 cells, and its activity was controlled by AMP, ADP, GTP, and CTP under saturating substrate concentrations. This study also provides new information as to the taxonomic relatedness of P. lemonnieri to other species classified within the Pseudomonas fluorescens homology group relative to regulation of pyrimidine biosynthesis.