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Updated: Aug 22, 2026
Oral Bacterial Infection and Shedding in Drosophila melanogaster
Published on: May 31, 2018
Pseudomonas aeruginosa relA contributes to virulence in Drosophila melanogaster
David L Erickson1, J Louise Lines, Everett C Pesci
1Department of Biological Sciences, University of Calgary, Alberta, Canada.
Abstract:
The stringent response is a mechanism by which bacteria adapt to nutritional deficiencies through the production of the guanine nucleotides ppGpp and pppGpp, produced by the RelA enzyme. We investigated the role of the relA gene in the ability of an extracellular pathogen, Pseudomonas aeruginosa, to cause infection. Strains lacking the relA gene were created from the prototypical laboratory strain PAO1 as well as the mucoid cystic fibrosis isolate 6106, which lacks functional quorum-sensing systems. The absence of relA abolished the production of ppGpp and pppGpp under conditions of amino acid starvation. We found that strains lacking relA exhibited reduced virulence in a D. melanogaster feeding assay. In conditions of low magnesium, the relA gene enhanced production of the cell-cell signal N-[3-oxododecanoyl]-l-homoserine lactone, whereas relA reduced the production of the 2-heptyl-3-hydroxy-4-quinolone signal during serine hydroxamate induction of the stringent response. In the relA mutant, alterations in the Pseudomonas quinolone system pathways seemed to increase the production of pyocyanin and decrease the production of elastase. Deletion of relA also resulted in reduced levels of the RpoS sigma factor. These results suggest that adjustment of cellular ppGpp and pppGpp levels could be an important regulatory mechanism in P. aeruginosa adaptation in pathogenic relationships.
Insights
The stringent response, regulated by RelA, is crucial for bacterial adaptation. Deleting the relA gene in Pseudomonas aeruginosa reduces its virulence and impacts key virulence factors, suggesting its importance in infection.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- The stringent response is a bacterial adaptation mechanism to nutrient deprivation, involving guanine nucleotides (ppGpp and pppGpp) synthesized by the RelA enzyme.
- Pseudomonas aeruginosa is an opportunistic extracellular pathogen significant in healthcare-associated infections and cystic fibrosis.
Purpose of the Study:
- To investigate the role of the relA gene in Pseudomonas aeruginosa virulence and adaptation during infection.
- To understand how RelA-mediated stringent response influences the production of virulence factors and regulatory molecules.
Main Methods:
- Generation of relA deletion mutants from P. aeruginosa strains PAO1 and 6106.
- Assessment of bacterial virulence using a Drosophila melanogaster feeding assay.
- Quantification of signaling molecules (N-[3-oxododecanoyl]-l-homoserine lactone and 2-heptyl-3-hydroxy-4-quinolone) and virulence factors (pyocyanin, elastase).
- Measurement of RpoS sigma factor levels.
Main Results:
- Absence of relA abolished ppGpp and pppGpp production under amino acid starvation.
- Strains lacking relA showed significantly reduced virulence in the D. melanogaster model.
- RelA influenced the production of quorum sensing signal N-[3-oxododecanoyl]-l-homoserine lactone and the Pseudomonas quinolone signal.
- relA mutants exhibited altered pyocyanin and elastase production and reduced RpoS levels.
Conclusions:
- The relA gene and stringent response play a critical role in P. aeruginosa virulence and adaptation.
- Regulation of ppGpp and pppGpp levels by RelA is a key factor in P. aeruginosa pathogenic relationships.
- Targeting the stringent response could be a potential strategy to combat P. aeruginosa infections.
