Influence of Myriophyllum spicatum-Derived Tannins on Gut Microbiota of Its Herbivore Acentria ephemerella

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Abstract
The submerged living larvae of Acentria ephemerella were fed in the laboratory with either M. spicatum or Potamogeton perfoliatus, two of their host plants. Larvae exhibited a reduced growth when fed M. spicatum, a freshwater angiosperm that contains high concentrations of tannins, secondary metabolites known for their herbivore-deterrent and antimicrobial properties. In this study, we investigated the influence of food-derived tannins on gut microbiota. Bacterial densities in the guts did not differ between the food regimes, ranging from 2.8 to 13.3 × 106cells per gut. Gut bacteria were characterized with cultivation techniques and subsequent identification of the strains by molecular methods. We isolated 17 bacterial strains belonging to all subdivisions, i.e., we identified α-, β- and γ-proteobacteria, Cytophyaga/Flavobacteria (CF) and several Gram-positive bacteria. All except one Gram-positive strain were found in the guts of larvae fed with P. perfoliatus. Gram-positive bacteria and bacteria of the CF cluster were more sensitive to polyphenol-containing extracts of M. spicatum in an agar diffusion assay than strains of the α- or γ-proteobacteria subdivision. Our results suggest an influence of food-derived tannins on gut microbiota in A. ephemerella.