Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2010
Publication Date: 9/13/2010
Citation: Olcott, M.H., Henkels, M.D., Rosen, K., Walker, F., Sneh, B., Loper, J.E., Taylor, B. 2010. Lethality and developmental delay of Drosophila melanogaster following ingestion of selected Pseudomonas fluorescens strains. PLoS One. 5(9):e12504. Interpretive Summary: Certain microorganisms function as biological control agents of plant diseases or arthropod pests, but few microorganisms can suppress both plant pathogens and insects. In earlier studies, we demonstrated that the bacterium Pseudomonas fluorescens strain Pf-5, a well-known biological control agent for suppression of plant disease, can kill certain insects when injected into larvae. In this study, we show that strain Pf-5 can kill fruit flies (Drosophila melanogaster) if the bacterium is incorporated into the insect diet. We tested three strains of P. fluorescens, and each of the strains had different effects on the insect. Of the three strains, Pf-5 was most toxic. When added to insect food at high cell densities, Pf-5 killed the fruit flies; at lower cell densities, Pf-5 caused delayed development of the insect. These experiments are the first to demonstrate that ingestion of P. fluorescens strain Pf-5 can kill insects, which indicates that this biological control agent may have potential for management of insect pests as well as plant diseases.
Technical Abstract: Pseudomonas fluorescens secretes antimicrobial compounds that promote plant health and provide protection from pathogens. We used a non-invasive feeding assay to study the toxicity of P. fluorescens strains Pf0-1, SBW25, and Pf-5 to Drosophila melanogaster. The three strains of P. fluorescens varied in their effects on D. melanogaster. Larval survival and development after Pf0-1 feeding was similar to that of control larvae, indicating that strain Pf0-1 is non-toxic to D. melanogaster larvae. In contrast, Pf-5 and SBW25 caused dose-dependent lethality, with adult survivors frequently displaying eye and wing morphological defects. In addition, larvae fed Pf-5 had a dose-dependent delay in the onset of metamorphosis relative to control-, Pf0-1-, and SBW25-treated larvae. Larvae fed either killed cells of Pf-5 or living cells of a gacA mutant of Pf-5 pupariated and survived at a similar frequency to controls, indicating that GacA is upstream of the exhibited survival and developmental toxicity of Pf-5. In contrast to Pf-5, treatment with SBW25 caused some animals to exhibit a profound fatal systemic melanization reaction at larval, pupal or adult stages. These experiments are the first to demonstrate that ingestion of P. fluorescens can delay the onset of metamorphosis in D. melanogaster and results in morphological defects in surviving adults that are independent of host survival.