Role of microbial eukaryotes (protists) in deep-sea primary production
Zusammenfassung der Projektergebnisse
As an offspring of the conducted research project a novel deep-sea Microbial Sampler-Submersible Incubation Device (MS-SID) was developed and constructed, which now allows unprecedented in situ experiments in the deep-sea. Using this device, we for the first time obtained reliable data quantifying the impact of protistanmediated carbon turnover in the deep-sea. Due to low activities and abundances of protists, we found that the role of protists in carbon turnover is negligible in the deepsea. This, however, does not apply to hotspots of chemoautotrophic activities in the deep-sea, such as the chemocline of anoxic hypersaline deep-sea lakes at the bottom (depth ca. 3000 m) of the eastern Mediterranean Sea. We could show that chemoclines and deep-water masses where new introductions of nutrients occur, support high protist phagotrophic activity and may be important habitats of deep-sea carbon cycling. Observed grazing activities appear to have a significant impact on prokaryotic populations, with important consequences for remineralization of nutrients in these deep water-column layers. The use of new technologies, such as the MS-SID used for the present project, are likely to provide estimations of in situ activities of both eukaryotic and prokaryotic communities with introduction of fewer sampling artifacts, and will improve our understanding of microbial food webs in habitats that are not yet well-understood. The establishment and test of a grazing technique, which minimizes experimental bias (use of natural fluorescently-labeled indigenous bacterial prey analogues in grazing experiments) occurred in a German stratified lake (Alatsee), due to logistics, costs, ease of access and previous research in this lake. The obtained data were of high scientific value provided the first information on phagotrophy and protistan-mediated carbon cycling in a stratified lake with a permanently anoxic hypolimnion. Due to failure and breakdown of the prototype version of MS-SID, which was intended to conduct the proposed research, a novel, more robust and sophisticated MS-SID had to be designed, constructed and tested. This delayed the project, and, as a consequence, assessment of specific grazing (i.e. identification of major grazers and the rate to which specific archaeal taxon groups involved in deep-sea chemolithoautotrophic production of organic carbon are predated) could not be conducted in the granted project period and is still due. The DEEP_C Coordinated Research Project (CRP), in which this individual project was embedded (ESF program EUROCORES: Ecological and Evolutionary Functional Genomics (EEFG)), received excellent final reviews by a board of external ESF-nominated reviewers. Part of this research was reported upon invitation in the DFG magazine “forschung” (02/2013) and is nominated for the international edition of this magazine. Several articles about this project were published in daily newspapers.
Projektbezogene Publikationen (Auswahl)
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Conference “Frontiers in Ecological and Evolutionary Genomics“, 2013, Noordwijkerhout, Netherlands: “Microbial eukaryote plankton community structure in the Matapan- Vavilov Deep (Mediterranean Sea).“
Filker S., Pachiadaki M., Oikonomou A., Yakimov M., Smedile F., Stoeck T.
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Meeting of the German Society of Protozoology, Wart-Weiningen, Switzerland 2013. “Protistan predation on prokaryotic population in a meromictic lake.“
Oikonomou A., Pachiadaki M. & Stoeck T.
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(2014) Protistan grazing in a meromictic freshwater lake with anoxic bottom water. FEMS Microbiol Ecol 87:691-703
Oikonomou, A., Pachiadaki, M. and Stoeck, T.
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In situ grazing experiments apply new technology to gain insights into deep-sea microbial food webs. Deep Sea Research Part II: Topical Studies in Oceanography, Volume 129, July 2016, Pages 223-231
Pachiadaki, M.G., Taylor, C., Oikonomou, A., Yakimov, M.M., Stoeck, T., and Edgcomb, V.
