Abstract
BackgroundThe fruit fly, Drosophila melanogaster, is a well-established model organism for probing the molecular and cellular basis of physiological and immune system responses of adults or late stage larvae to bacterial challenge. However, very little is known about the consequences of bacterial infections that occur in earlier stages of development. We have infected mid-second instar larvae with strains of Pseudomonas fluorescens to determine how infection alters the ability of larvae to survive and complete development.Methodology/Principal FindingsWe mimicked natural routes of infection using a non-invasive feeding procedure to study the toxicity of the three sequenced P. fluorescens strains (Pf0-1, SBW25, and Pf-5) to Drosophila melanogaster. Larvae fed with the three strains of P. fluorescens showed distinct differences in developmental trajectory and survival. Treatment with SBW25 caused a subset of insects to die concomitant with a systemic melanization reaction at larval, pupal or adult stages. Larvae fed with Pf-5 died in a dose-dependent manner with adult survivors showing eye and wing morphological defects. In addition, larvae in the Pf-5 treatment groups showed a dose-dependent delay in the onset of metamorphosis relative to control-, Pf0-1-, and SBW25-treated larvae. A functional gacA gene is required for the toxic properties of wild-type Pf-5 bacteria.Conclusions/SignificanceThese experiments are the first to demonstrate that ingestion of P. fluorescens bacteria by D. melanogaster larvae causes both lethal and non-lethal phenotypes, including delay in the onset of metamorphosis and morphological defects in surviving adult flies, which can be decoupled.
Highlights
The fruit fly, Drosophila melanogaster, is a well-established model organism for the study of host response to microbial infection and animal development
8761% of larvae fed with P. fluorescens strain Pf0-1 at doses ranging from 103 to 109 cfu/plate survived to adulthood (Fig. 2, Fig. S1), which is not different from the survival of larvae in the control treatment group (X2 = 0.95, Df = 6, P = 0.99)
Only 30610% of larvae fed with a yeast suspension containing 107 or 109 cells of SBW25 survived to adulthood (Fig. 2A, Fig. S1), which is significantly different from the control treatment group (X2 = 61.1, Df = 1, P,0.00001)
Summary
The fruit fly, Drosophila melanogaster, is a well-established model organism for the study of host response to microbial infection and animal development. A recent study demonstrated that fitD confers strong insecticidal activity, which was exhibited when Pf-5 or the closelyrelated strain CHA0 was injected into larvae of two insect species, the tobacco hornfworm Manduca sexta and the greater wax moth Galleria mellonella [10]. These results highlighted the exciting possibility that strains of P. fluorescens have additional previously-unappreciated insecticidal activities. We have infected mid-second instar larvae with strains of Pseudomonas fluorescens to determine how infection alters the ability of larvae to survive and complete development
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