Salinity shifts characterize a boundary which is one of the most difficult barriers to cross for organisms in all
three domains of life . While mechanisms to cope with high salt concentrations are relatively well studied in prokaryotes, they are still largely unknown in protists (with the exception of the model algae Dunaliella salina). While there is evidence that many protists have narrow ranges of salt tolerance [45, 46], some taxa are known to occur under a wide range of salinities, from freshwater to hypersaline . One example is the ciliate Cyclidium glaucoma, which may explain the occurrence IAP inhibitor of some of the same phylotypes in haloclines and brines of specific DHABs. Other examples are likely to exist. In contrast, adaptations to anoxia in GANT61 chemical structure Ciliates are well known. Ciliates are one of the most successful eukaryotic taxon groups in hypoxic and anoxic habitats. In their long evolutionary history, they have acquired several strategies that allow for an anaerobic lifestyle, including hydrogenosomes [49, 50], anaerobic mitochondria , and/or symbiotic
networks [52, 53]. The high taxonomic diversity of anaerobe ciliates includes taxa such as Nyctotherus, Loxodes, Pleuronema, Strombidium, Trimyema, Cyclidium and Metopus, some of which were also detected in our genetic diversity survey. Electron microscopy and fluorescence in situ hybridization assays provide unbiased evidence that the genetic signatures we detected in our rRNA-targeted gene survey can be assigned to ciliates living
in the selleck screening library DHABs rather than reflecting ancient nucleic acids. (Figure 5, [25, 54]). Taking advantage of phylotypes that we detected exclusively in specific habitats and phylotypes that can be found in several habitats with distinct hydrochemical CYTH4 characteristics, we may assume that the latter have a character of more generalist taxa compared to the more locally restricted phylotypes. The total number of observed taxon groups is 102 distributed over eight different datasets (samples or habitats) (Additional file 1: Figure S1). In those eight samples there are 13 generalist taxonomic groups that appeared simultaneously in at least six of the datasets. Only four taxonomic groups appeared in all of the eight datasets. Specialists, i.e. taxa that are restricted to a single unique habitat account for 34 different taxonomic groups. This results in a specialist/generalist ratio of 8.5 to 1, indicating a high specialization of taxa in the habitats under study. However, there is a limitation to infer the autecology of specific evolutionary lineages based on sequence data and microscopy evidence . We do not make any attempt to explain the presence or absence of specific phylotypes in individual samples, and we instead focus only on community level ciliate diversity.