Ciliates play apivotal role in the microbial food web of lakes. Due to their broad food rangethey act at different trophic levels. But knowledge about ciliates in Lake Zurich is scarce. The last publications originate from the 60ies and described observations of pelagic ciliate species only. My master thesis was the firstquantitative analysis of pelagic ciliates (during the spring bloom period) and included also a qualitative study of benthic ciliates in Lake Zurich.
In my PhD thesis, I investigate the ecology of ciliates in general but especially the interactions between ciliates and the main primary producer of Lake Zurich, the cyanobacterium Planktothrix rubescens. This cyanobacterium is supposed
to be toxic for all eukaryotes due to the cell internal storage of microcystins and other harmful secondary metabolites. Interestingly, in Lake Zurich several protistan species have been discovered which prefer P. rubescens as their main food source. In my PhD-project I will focus on two ciliate species, Obertrumia
aurea (Nassophorea) and Trithigmostoma cucullulus (Phyllopharyngea). Meanwhile, I can work with several clonal isolates which are kept on a diet of an axenic P. rubescens strain (A7). I study the aut- and the synecology of the isolates with a special focus on the interactions with the toxic
- P.rubescens shows increasing dominance in Lake Zurich but there mass developments of cyanobacteria feeding ciliates can not be observed. Which factors are responsible for the population control of ciliates in the lake?
- Which influence have secondary metabolites like microcystins (MCs) on growth of ciliates?
- Which strategies did ciliates develop to deal with their toxic diet?
- Do ciliates show comparable growth dynamics when fed with the toxic P. rubescens strain A7 in comparison to being feed with a MCs-free P. rubescens strain?
- Can MCs be detected in ciliate cells, and is their MCs content changing with prolonged digestion time?
- Can ciliates be maintained in axenic cultures or are accompanying bacteria required for a prolonged maintenance of cultures? Are these bacteria phylogenetically related to known MCs degrading strains?
- Do ciliates harbour intracellular bacteria from phylogenetic groups which are known to degrade MCs?
- Isolation and cultivation of ciliates
- Silver impregnation of ciliates (Protargol staining)
- Microscopy (bright-field, DIC, phase contrast) and image analysis systems
- Transmissionelectron microscopy
- HPLC (analysis of microcystins)
- Elsevier Poster Award, 1st Price, VI, European Congress of Protistology, July 25-29, Berlin, Germany. Title of the poster: Feeding of ciliates on toxic filamentous cyanobacteria in Lake Zurich (Switzerland) Authors: T. Posch, B. Eugster
- Swiss Hydrobiology- Limnology Award 2011 for the best master thesis, Foundation of Hydrobiology and Limnology in Switzerland. Title of the thesis: Diversity of planktonic and benthic ciliates (Ciliophora) in Lake Zurich
List of Publications
Derlon, N., Koch, N., Eugster, B., Posch, T., Pernthaler, J., Pronk, W., and Morgenroth, E. (2013). Activity of metazoa governs biofilm structure formation and enhances permeate flux during Gravity-Driven Membrane (GDM) filtration. Water Res 47, 2085-2095.
Pomati, F., Kraft, N.J.B., Posch, T., Eugster, B., Jokela, J., and Ibelings, B.W. (2013). Individual cell based traits obtained by scanning flow-cytometry show selection by biotic and abiotic environmental factors during a phytoplankton spring bloom. PLOS ONE 8 (8), 1-11.
Eckert, E.M., Salcher, M.M., Posch, T., Eugster, B., and Pernthaler, J. (2012) Rapid successions affect microbial N-acetyl-glucosamine uptake patterns during a lacustrine spring phytoplankton bloom. Environ Microbiol 14:794-806