Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/30/2011
Publication Date: 6/1/2011
Citation: Olcott, M.H., Henkels, M.D., Rosen, K.L., Walker, F.L., Loper, J.E., Taylor, B.J. 2011. Toxicity of Pseudomonas fluorescens strain Pf-5 to Drosophila larvae is due to downstream gene targets of the GacA/GacS signal transduction system.Northwest Devlopmental Biology Meeting Abstract. Interpretive Summary:
Technical Abstract: Given the vast number of microorganisms in the environment, surprisingly, only a few are lethal or cause morbidity to host organisms. Pseudomonas spp are a diverse genus of Gram-negative bacteria commonly found in soil, water, or in association with plants and animals. Pseudomonas fluorescens has been implicated in Crohn’s disease and shown to cause opportunistic infections in humans. The Pf-5 strain was isolated from the plant rhizosphere and demonstrated to suppress plant diseases due to its antimicrobial and insecticidal properties. Using a feeding assay, we have demonstrated that ingestion of the Pf-5 strain by D. melanogaster larvae causes dose-dependent lethality as well as sub-lethal phenotypes, such as a delay in metamorphosis and the development of morphological defects in adult survivors. Many of the developmental and morphological phenotypes associated with Pf-5 ingestion, including small body size, loss of fat body integrity and prolonged larval development, are reminiscent of larval responses to starvation. The toxicity and pathogenicity of different Pseudomonas spp. is due to the production and secretion of a large number of secondary metabolites under the control of the GacS/GacA signal transduction system. In Pf-5, the GacS/GacA system has been shown to regulate the expression of about 600 genes, including those encoding secondary metabolite and exoenzyme production, stress and metabolism responses and motility. To better understand the molecular determinants of Pf-5 toxicity to Drosophila larvae, we fed larvae Pf-5 gacA mutant bacteria and found significant reduction in toxicity. We have initiated studies to identify the downstream target genes by testing Pf-5 strains in which genes expected or known to produce insecticidal toxins or attack host defenses have been mutated. Our results suggest that relatively few gene targets of GacA/GacS may be responsible for the larval lethality, delay in metamorphosis and defects in adult structures.