Our research combines multiple approaches – from amplicon data analyses to genome and transcriptome analyses to functional experiments – in order to infer protistan diversity patterns shaped by environmental factors as well as their cellular responses to environmental change.
Microbial community composition and species turnover along salt gradients
Salinity is one of the most important factors globally selecting and structuring microbial assemblages as it acts as a transition barrier between freshwater and marine environments. Such marine-freshwater transitions are relatively rare events and the number of taxa that can thrive in fresh- and saltwater environments simultaneously is limited, mostly because of osmotic and ionic gradients, which require adaptive evolutions at high energetic costs. For a long time, it has been suggested that microbial eukaryotes (protists) have greater difficulties coping with the selective effect of high salinity, resulting in large decreases in the number of species as salinity increases. This thinking has led to the believe that microbial eukaryotes are a poorly represented domain in high salinity environments compared to prokaryotes and mostly restricted to a limited number of groups (preferentially fungi, a few algae and heterotroph flagellates). But, as most information about microbial eukaryote diversity in such environments derives from microscopy and fingerprinting approaches, the true extent of their diversity in these extreme habitats is still obscure. In our projects we analyze microbial eukaryotes of various hypersaline environments (salinity between 4 - 44%) distributed all over the earth.
Haloadaptation strategies in halotolerant, heterotroph ciliates
The specific distribution patterns of microbial eukaryotes raise the question for specific adaptation strategies to cope with different external salt concentrations. While high-salt adaptation strategies have been a focus of prokaryote microbiology for a long time, microbial eukaryotes are a sadly and severely neglected group in this respect. For halophilic prokaryotes, two fundamentally different processes as adaptations to high-salt environments are described: the “salt-in-strategy” involves the intracellular accumulation of molar concentrations of chloride and potassium, whereas the “salt-out-strategy” excludes salts from the cytoplasm while producing high concentrations of organic compatible solutes, which are inert and do not greatly interfere with enzymatic activities. Using transcriptome and genome analyses, as well as mechanistic approaches, we investigate the ecophysiology of halotolerant microeukaryotes, in specific heterotroph ciliates, which exhibit different salt tolerance ranges, to fill this gap in knowledge.