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Aquatic Microbial Ecology

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AME 41:271-280 (2005)  -  doi:10.3354/ame041271

Trophic upgrading of picocyanobacterial carbon by ciliates for nutrition of Daphnia magna

Dominik Martin-Creuzburg1, 2, *, Alexandre Bec1, 3, Eric von Elert1

1Limnological Institute, Mainaustrasse 252, University of Konstanz, 78464 Konstanz, Germany
2Present address: Department of Animal Ecology I, Universitätsstrasse 30, University of Bayreuth, 95440 Bayreuth, Germany
3Present address: Laboratoire de Biologie des Protistes, UMR CNRS 6023, Université Blaise Pascal, 63177 Aubiere cedex, France

ABSTRACT: Unicellular picocyanobacteria, such as species of the genus Synechococcus, are unsuitable for supporting growth and reproduction of Daphnia spp. In Synechococcus spp., long-chain polyunsaturated fatty acids (PUFAs) and sterols are absent, which leads to a low carbon transfer efficiency at the picocyanobacteria–Daphnia spp. interface. Herein, we address the question as to whether ciliates can serve as a trophic link between picocyanobacterial production and Daphnia spp. production, thereby upgrading the nutritional value of a picocyanobacterial food source by producing essential lipids such as PUFAs or sterols. In simplified experimental food chains consisting of 1 of 2 different Synechococcus strains, the ciliates Colpidium campylum or Cyclidium sp., and D. magna, we provided evidence that predation on ciliates by Daphnia spp. allows access to picocyanobacterial production. Since daphnids are primarily sterol-limited when grown on the picocyanobacteria Synechococcus spp., the observed trophic upgrading of Synechococcus food-quality by intermediary ciliates is most probably due to the addition of sterols or sterol-like compounds that (at least partly) release Daphnia spp. from sterol limitation. The absence of sterols in the ciliates used in the present study suggests that tetrahymanol and/or hopanoids provide functional equivalents of sterols not only in ciliates but also in Daphnia spp., thereby leading to enhanced growth of the cladocerans.

KEY WORDS: Synechococcus spp. · Colpidium campylum · Cyclidium spp. · Sterols · Tetrahymanol · Hopanoids

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