Isolation and characterization of a dihydropyrimidine dehydrogenase mutant of Pseudomonas chlororaphis

Control of a pyrimidine ribonucleotide salvage pathway in Pseudomonas oleovorans

The control of a pyrimidine ribonucleotide salvage pathway in the bacterium Pseudomonas oleovorans ATCC 8062 was studied. This bacterium is important for its ability to synthesize polyesters as well as for its increasing clinical significance in humans. The pyrimidine salvage pathway enzymes pyrimidine nucleotide N-ribosidase and cytosine deaminase were investigated in P. oleovorans ATCC 8062 under selected culture conditions. Initially, the effect of carbon source on the two pyrimidine salvage enzymes in ATCC 8062 cells was examined and it was observed that cell growth on the carbon source succinate generally produced higher enzyme activities than did glucose or glycerol as a carbon source when ammonium sulfate served as the nitrogen source. Using succinate as a carbon source, growth on dihydrouracil as nitrogen source caused a 1.9-fold increase in the pyrimidine nucleotide N-ribosidase activity and a 4.8-fold increase in cytosine deaminase activity compared to the ammonium sulfate-grown cells. Growth of ATCC 8062 cells on cytosine or dihydrothymine as a nitrogen source elevated deaminase activity by more than double that observed for ammonium sulfate-grown cells. The findings indicated a relationship between this pyrimidine salvage pathway and the pyrimidine reductive catabolic pathway since growth on dihydrouracil appeared to increase the degradation of the pyrimidine ribonucleotide monophosphates to uracil. The uracil produced could be degraded by the pyrimidine base reductive catabolic pathway to β-alanine as a source of nitrogen. This investigation could prove helpful to future work examining the metabolic relationship between pyrimidine salvage pathways and pyrimidine reductive catabolism in pseudomonads.

Identification of dihydropyrimidine dehydrogenase as a virulence factor essential for the survival of Entamoeba histolytica in glucose-poor environments

Adaptation to nutritional changes is a key feature for successful survival of a pathogen within its host. The protozoan parasite Entamoeba histolytica normally colonizes the human colon and in rare occasions, this parasite spread to distant organs, such as the liver. E. histolytica obtains most of its energy from the fermentation of glucose into ethanol. In this study, we were intrigued to know how this parasite reacts to changes in glucose availability and we addressed this issue by performing a DNA microarray analysis of gene expression. Results show that parasites that were adapted to growth in absence of glucose increased their virulence and altered the transcription of several genes. One of these genes is the dihydropyrimidine dehydrogenase (DPD), which is involved in degradation of pyrimidines. We showed that this gene is crucial for the parasite's growth when the availability of glucose is limited. These data contribute to our understanding of the parasite's ability to survive in glucose-poor environments and reveal a new role for the DPD enzyme.

A gene cluster involved in pyrimidine reductive catabolism from Brevibacillus agri NCHU1002

Genes involved in pyrimidine reductive catabolism (pyd) were isolated from a moderate thermophile, Brevibacillus agri NCHU1002, and nine ORFs in an 8.2-kb DNA fragment were identified by DNA sequence analysis. The pyd gene cluster included three closely spaced ORFs, designated pydA, pydB, and pydC, transcribed in the same orientation. Based on their amino acid sequence identity and enzyme activity assay, the gene products were identified as dihydropyrimidine dehydrogenase (PydA), dihydropyrimidinase (PydB), and beta-alanine synthase (PydC). Northern blot and primer extension analyses revealed that the pydBC genes are induced by dihydrouracil and regulated under the control of sigma(54) recognized promoter at transcriptional level as a polycistronic operon. All results indicate that the pydABC genes participate in the pathway of the pyrimidine reductive catabolism. This is the first bacterial pyd gene cluster to be reported.

Pyrimidine ribonucleoside catabolic enzyme activities of Pseudomonas pickettii

Pyrimidine ribonucleoside catabolic enzyme activities of the opportunistic pathogen Pseudomonas pickettii were examined. Of the pyrimidine and related compounds tested, only dihydrouracil (nitrogen source) and ribose (carbon source) supported growth. Thin-layer chromatographic separation of the uridine and cytidine catabolities produced by P. pickettii extracts indicated that this pseudomonad contained nucleoside hydrolase activity. Its presence was confirmed by enzyme assay. Hydrolase activity was elevated in both glucose- and ribose-grown cells relative to succinate-grown cells. Nucleoside hydrolase activity was depressed when dihydrouracil served as a nitrogen source. Cytosine deaminase activity was present in extracts prepared from succinate-, glucose- or ribose-grown cells when (NH4)2SO4 served as the nitrogen source although cells grown on glucose or ribose exhibited a higher enzyme activity. Cytosine deaminase activity was not detected in extracts prepared from cells grown on dihydrouracil as a nitrogen source. Both dihydropyrimidine dehydrogenase and dihydropyrimidinase activities were measurable in P. pickettii. The dehydrogenase activity was higher with NADH than with NADPH as its nicotinamide cofactor when uracil served as its substrate. Carbon source did not affect dehydrogenase or dihydropyrimidinase activity greatly but both activities were diminished in cells grown on the nitrogen source dihydrouracil.