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Infection and Immunity, October 2004, p. 5638-5645, Vol. 72, No. 10
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.10.5638-5645.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Pseudomonas aeruginosa relA Contributes to Virulence in Drosophila melanogaster

David L. Erickson,1,{dagger} J. Louise Lines,2 Everett C. Pesci,2 Vittorio Venturi,3 and Douglas G. Storey1,4*

Departments of Biological Sciences,1 Microbiology and Infectious Diseases University of Calgary, Calgary, Alberta, Canada,4 Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, North Carolina,2 Bacteriology Group, International Centre for Genetic Engineering & Biotechnology, Trieste, Italy3

Received 19 November 2003/ Returned for modification 26 February 2004/ Accepted 30 June 2004

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.

* Corresponding author. Mailing address: Department of Biological Sciences, 2500 University Dr. N.W., Calgary, Alberta, Canada T2N 1N4. Phone: (403) 270-5274. Fax: (403) 289-9311. E-mail: storey{at}ucalgary.ca.

Editor: V. J. DiRita

{dagger} Present address: Laboratory of Human Bacterial Pathogenesis, Rocky Mountain Laboratories, NIAID, NIH, Hamilton, MT 59840.

Infection and Immunity, October 2004, p. 5638-5645, Vol. 72, No. 10
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.10.5638-5645.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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