Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Chemistry and Biochemistry


Many of the Pseudomonas are opportunistic pathogens and it has been suggested that they may have the potential to serve as biological control agents. Pseudomonads have been implicated in food spoilage as well as plant disease. It has been determined that some species in this genus have the capability of utilizing pyrimidines as sole nitrogen sources. The purpose of this study was to investigate the growth on and reductive catabolism of pyrimidines by Pseudomonasfluorescens cells. This microorganism was grown in a succinate (0.4%) mjnirnal medium of Stanier where the nitrogen source was varied. Ten nitrogen sources and one control lacking a nitrogen source were used during the course of this experiment. The cultures were shaken at 200 revolutions per minute at 30°C. Growth of the bacterial culture was monitored at 600 nm. It was determined that P. jluorescens could utilize uracil, thymine, dihydrouracil dihydrothymine, 13-alanine, 13-aminoisobutyric acid, cytosine, and ammonium sulfate as nitrogen sources. The reductive pathway is known to exist in P. fluorescens. This investigation determined that the three enzymes in the reductive pathway are required for pyrimidine catabolism. The initial enzyme is dihydropyrimidine dehydrogenase that catalyzes the reaction of uracil or thymine to dihydrouracil or dihydrothymine. Dihydropyrimidinase, the second enzyme in the pathway, catalyzes the reaction of the dihydropyrimidine derivatives to their N-carbamoyl-J3-amino acids, namely Ncarbamoyl- J3-alanine or N-carbamoyl-J3-aminoisobutyric acid, respectively. The final catalytic enzyme, N-carbamoyl-J3-amidohydrolase, produces J3-alanine or 13-aminoisobutyric acid from N-carbarnoyl-J3-alanine and N-carbamoyl-J3-arninoisobutyric acid, respectively. It can be concluded from the enzyme activities that P.jluorescens degrades pyrimidine bases by way of a reductive pathway to provide a source of nitrogen.

Library of Congress Subject Headings

Pyrimidines -- Metabolism
Pseudomonas fluorescens



Number of Pages



South Dakota State University