Microbe-Dependent and Nonspecific Effects of Procedures To Eliminate the Resident Microbiota from Drosophila melanogaster

Abstract

bComparisons of animals bearing and lacking microorganisms can offer valuable insight into the interactions between animal hosts and their resident microbiota. Most hosts are naturally infected, and therefore, these comparisons require specific procedures (e.g., antibiotic treatment or physical exclusion of microorganisms) to disrupt the microbiota, but the potential for confounding nonspecific effects of the procedure on the traits of the host exists. Microbe-dependent and nonspecific effects can be discriminated by using multiple procedures: microbe-dependent effects are evident in hosts made microbe free by different procedures, but nonspecific effects are unique to individual procedures. As a demonstration, two procedures, oral administration of chlortetracycline (50 g ml ؊1 diet) and microbiota removal by egg dechorionation, were applied to Drosophila melanogaster in a 2-by-2 factorial design. Microorganisms were undetectable in flies from dechorionated eggs and reduced by >99% in chlortetracycline-treated flies. Drosophila flies subjected to both protocols displayed an extended preadult development time, suggesting that the microbiota promotes the development rate. Female chlortetracycline-treated flies, whether from untreated or dechorionated eggs, displayed reduced protein content and egg fecundity, which could be attributed to the nonspecific effect of the antibiotic. We recommend that procedures used to disrupt the microbiota of animals should be selected, following systematic analysis of alternative mechanistically distinct procedures, on the basis of two criteria: those that achieve the greatest reduction (ideally, elimination) of the microbiota and those that achieve minimal nonspecific effects.

Interspecies Interactions Determine the Impact of the Gut Microbiota on Nutrient Allocation in Drosophila melanogaster

“…Microbiota-dependent reduction of fly glucose content is evident at low bacterial densities, for example, 400 CFU in flies monoassociated with A. pomorum (this study) and 120 CFU in antibiotic-treated flies (19). The microbiota-dependent reduction in TAG content is, in contrast, strongly dependent on the abundance of Acetobacter.…”

“…These gut bacteria have profound effects on the nutritional traits of Drosophila. Generally, axenic Drosophila (i.e., reared under germfree conditions) display extended larval development time and hyperglycemia, and the traits of conventional Drosophila (i.e., with unmanipulated microbiota) are recapitulated, partially or completely, in axenic hosts reinfected with Acetobacter, Lactobacillus, or undefined microbial inocula derived from conventional flies (19)(20)(21)(22). However, the results across the several studies are not fully consistent, perhaps reflecting variations in the diet and genotypes of the host and bacteria.…”

Stable Host Gene Expression in the Gut of Adult Drosophila melanogaster with Different Bacterial Mono-Associations

“…After 4–6 hours, embryos were transferred into a sterile 100 micron cell strainer (BD Falcon #352360 and rinsed with Milli-Q water (EMD Millipore). Conventional animals were generated by transferring ~100 water-rinsed embryos to sterile YG diet (10% active dry yeast, 10% glucose, 1.2% agar, 0.42% propionic acid [39] sterilized by autoclaving).…”

Studying host-microbiota mutualism in Drosophila: Harnessing the power of gnotobiotic flies

“…Of note, bleaching and/or antibiotic treatment can lower fly viability and fecundity and have certain unintended negative cellular and systemic effects on the host. [41] Therefore, the studies using germ-free flies mandate careful and thorough controls. In the following sections, we review a few seminal gnotobiotic Drosophila studies that have uncovered important molecular mechanisms governing host-microbiota interaction.…”