Regulation of pyrimidine synthesis in Pseudomonas mendocina

Regulation of the de novo pyrimidine biosynthetic enzymes in the bacterium Pseudomonas mendocina was examined when its cells were grown on succinate as a carbon source. When P. mendocina was grown in the presence of orotic acid or uracil, the de novo enzyme activities were depressed with dihydroorotase activity being significantly depressed after uracil addition. Following pyrimidine limitation of a uracil auxotroph of P. mendocina deficient for orotate phosphoribosyltransferase activity, the pyrimidine biosynthetic pathway enzyme activities were affected indicating possible regulation at the level of enzyme synthesis. Of the de novo pathway enzymes assayed, dihydroorotate dehydrogenase exhibited the highest increase in its activity. The regulation of the pyrimidine biosynthetic pathway by pyrimidines in P. mendocina appeared similar to what was previously observed for the taxonomically-related species P. stutzeri.