Composition and Stability of the Microbial Community inside the Digestive Tract of the Aquatic Crustacean <Emphasis Type="Italic">Daphnia magna</Emphasis> |
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Authors: | Heike M Freese Bernhard Schink |
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Institution: | 1.Department of Biology, Microbial Ecology,University of Konstanz,Konstanz,Germany |
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Abstract: | Small filter-feeding zooplankton organisms like the cladoceran Daphnia spp. are key members of freshwater food webs. Although several interactions between Daphnia and bacteria have been investigated, the importance of the microbial communities inside Daphnia guts has been studied only poorly so far. In the present study, we characterised the bacterial community composition inside
the digestive tract of a laboratory-reared clonal culture of Daphnia magna using 16S rRNA gene libraries and terminal-restriction length polymorphism fingerprint analyses. In addition, the diversity
and stability of the intestinal microbial community were investigated over time, with different food sources as well as under
starvation stress and death, and were compared to the community in the cultivation water. The diversity of the Daphnia gut microbiota was low. The bacterial community consisted mainly of Betaproteobacteria (e.g. Limnohabitans sp.), few Gammaproteobacteria (e.g. Pseudomonas sp.) and Bacteroidetes that were related to facultatively anaerobic bacteria, but did not contain typical fermentative or
obligately anaerobic gut bacteria. Rather, the microbiota was constantly dominated by Limnohabitans sp. which belongs to the Lhab-A1 tribe (previously called R-BT065 cluster) that is abundant in various freshwaters. Other
bacterial groups varied distinctly even under constant cultivation conditions. Overall, the intestinal microbial community
did not reflect the community in the surrounding cultivation water and clustered separately when analysed via the Additive
Main Effects and Multiplicative Interaction model. In addition, the microbiota proved to be stable also when Daphnia were exposed to bacteria associated with a different food alga. After starvation, the community in the digestive tract was
reduced to stable members. After death of the host animals, the community composition in the gut changed distinctly, and formerly
undetected bacteria were activated. Our results suggest that the Daphnia microbiota consists mainly of an aerobic resident bacterial community which is indigenous to this habitat. |
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