Effect of carbon source on pyrimidine biosynthesis in Pseudomonas oryzihabitans

The effect of carbon source on the regulation of pyrimidine biosynthesis in the opportunistic human pathogen Pseudomonas oryzihabitans was studied at the level of enzyme synthesis. Although pyrimidine supplementation of glucose-grown Ps. oryzihabitans cells produced a slight but statistically significant effect on the de novo pyrimidine biosynthetic pathway enzyme activities, catabolite repression of the enzyme activities by glucose appeared to be occurring. Pyrimidine limitation experiments undertaken using an orotidine 5'-monophosphate decarboxylase mutant strain grown on glucose indicated that repression of enzyme synthesis by pyrimidines was occurring. Following pyrimidine limitation of the mutant strain cells, dihydroorotase and dihydroorotate dehydrogenase activities were found to about double while aspartate transcarbamoylase and orotate phosphoribosyltransferase activities were slightly elevated compared to their activities in the mutant strain cells grown on excess uracil.