Friday April 23^rd presentation

Sara will present her research project:

Evaluation of virulence in wild type and pyrimidine auxotrophs of Pseudomonas aeruginosa using the eukaryotic model system Caenorhabditis elegans

Abstract:

The pyrimidine biosynthetic pathway affects essentially all aspects of cellular metabolism. Thus, studies of pyrimidines are important as the pathway is directly involved in DNA, RNA, cell membrane and cell wall biosynthesis in bacteria. Pyrimidine metabolism has been the subject of intensive research as several enzymes of the pathway are potential targets of chemotherapy. While isolating pyrimidine-requiring mutants in Pseudomonas aeruginosa PAO1, two pyrC genes were discovered, each encoding a functional dihydroorotase (DHOase) enzyme, such that it was necessary to knock out both pyrC genes in order to create a true DHOase mutant (Brichta, 2003). This DHOase mutant required uracil for growth and grew at wild type rates in uracil minimal medium.  Despite the similarity of growth rates the mutant was impaired in its virulence response.  While an in vivo model involving Caenorhabditis elegans has been established in order to study virulence in wild type P. aeruginosa PAO1 (Darby et al, 1999), the connection between pyrimidine auxotrophy and virulence had not been reported previously.  Prior studies of the DHOase mutant strains involved in vitro measurements of virulence factor production.  Now we are interested in learning the ability of the PAO1 mutants to show virulence in vivo.  Here we show that the DHOase double knockout is unable to kill the nematode.  In addition, the individual pyrC ^– pyrC2⁺ and the pyrC⁺ pyrC2^- knockouts were tested for virulence and results show that the pyrC^- pyrC2⁺ is more virulent than the pyrC⁺ pyrC2^- knockout.  Use of the C. elegans model has allowed us to further demonstrate the virulence defect of the DHOase mutant strain, and moreover has shown a difference between the virulence capabilities of the individual pyrC knockout mutants. This suggests that the pyrimidine intermediates play an important role in the virulence response of P. aeruginosa.