Impaired virulence factor production in a dihydroorotate dehydrogenase mutant (pyrD) of Pseudomonas aeruginosa.

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Previous research in our laboratory showed that when knockout mutations were created in the pyrB and pyrC genes of the pyrimidine pathway in Pseudomonas aeruginosa, not only were the resultant mutants auxotrophic for pyrimidines but they were also impaired in virulence factor production. Such a correlation had not been previously reported for P. aeruginosa, a ubiquitous opportunistic pathogen in humans. In an earlier study it was reported that mutants blocked in one of the first three enzymes of the pyrimidine pathway in the non-pathogenic strain P. putida M produced no pyoverdin pigment while mutants blocked in the later steps produced ... continued below

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Ralli, Pooja December 2005.

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  • Ralli, Pooja

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Previous research in our laboratory showed that when knockout mutations were created in the pyrB and pyrC genes of the pyrimidine pathway in Pseudomonas aeruginosa, not only were the resultant mutants auxotrophic for pyrimidines but they were also impaired in virulence factor production. Such a correlation had not been previously reported for P. aeruginosa, a ubiquitous opportunistic pathogen in humans. In an earlier study it was reported that mutants blocked in one of the first three enzymes of the pyrimidine pathway in the non-pathogenic strain P. putida M produced no pyoverdin pigment while mutants blocked in the later steps produced copious amounts of pigment, just like the wild type. This study probed for the same connection between pyrimidine auxotrophy and pigment production applied in P. aeruginosa. To that end a knockout mutation was created in pyrD, the fourth step in the pyrimidine pathway which encodes dihydroorotate dehydrogenase. The resulting mutant required pyrimidines for growth but produced wild type pigment levels. Since the pigment pyoverdin is a siderophore it may also be considered a virulence factor, other virulence factors were quantified in the mutant. These included casein protease, hemolysin, elastase, swimming, swarming and twitching motility, and iron binding capacity. In all cases these virulence factors were significantly decreased in the mutant. Even supplementing with uracil did not attain wild type levels. Starvation of the pyrimidine mutant for uracil caused increased specific activity of the pyrimidine enzymes, suggesting that regulation of the pyrimidine pathway occurred at the level of transcription. This effect has also been reported for P. oleovorans. The present research consolidates the idea that pyrimidine auxotrophs cause decreased pathogenicity in P. aeruginosa. Such a finding may open the search for chemotherapy targets in cystic fibrosis and burn victims where P. aeruginosa is an infecting agent.

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  • December 2005

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  • Feb. 15, 2008, 4:30 p.m.

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  • March 3, 2008, 12:05 p.m.

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Ralli, Pooja. Impaired virulence factor production in a dihydroorotate dehydrogenase mutant (pyrD) of Pseudomonas aeruginosa., dissertation, December 2005; Denton, Texas. (digital.library.unt.edu/ark:/67531/metadc4940/: accessed September 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .