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We isolated an encysted ciliate from a geothermal field in Iceland. The morphological features of this isolate fit the descriptions of Dexiotricha colpidiopsis (Kahl, 1926) Jankowski, 1964 very well. These comprise body shape and size in vivo, the number of somatic kineties, and the positions of macronucleus and contractile vacuole. Using state-of-the-art taxonomic methods, the species is redescribed, including phylogenetic analyses of the small subunit ribosomal RNA (SSU rRNA) gene as molecular marker. In the phylogenetic analyses, D. colpidiopsis clusters with the three available SSU rRNA gene sequences of congeners, suggesting a monophyly of the genus Dexiotricha. Its closest relative in phylogenetic analyses is D. elliptica, which also shows a high morphological similarity. This is the first record of a Dexiotricha species from a hot spring, indicating a wide temperature tolerance of this species at least in the encysted state. The new findings on D. colpidiopsis are included in a briefly revision of the scuticociliate genus Dexiotricha and an identification key to the species.
Słowa kluczowe: Dexiotricha, hot spring, morphology, phylogeny, SSU rRNA gene
The analysis of benthic bacterial community structure has emerged as a powerful alternative to traditional microscopy-based taxonomic approaches to monitor aquaculture disturbance in coastal environments. However, local bacterial diversity and community composition vary with season, biogeographic region, hydrology, sediment texture, and aquafarm-specific parameters. Therefore, without an understanding of the inherent variation contained within community complexes, bacterial diversity surveys conducted at individual farms, countries, or specific seasons may not be able to infer global universal pictures of bacterial community diversity and composition at different degrees of aquaculture disturbance. We have analyzed environmental DNA (eDNA) metabarcodes (V3–V4 region of the hypervariable SSU rRNA gene) of 138 samples of different farms located in different major salmon-producing countries. For these samples, we identified universal bacterial core taxa that indicate high, moderate, and low aquaculture impact, regardless of sampling season, sampled country, seafloor substrate type, or local farming and environmental conditions. We also discuss bacterial taxon groups that are specific for individual local conditions. We then link the metabolic properties of the identified bacterial taxon groups to benthic processes, which provides a better understanding of universal benthic ecosystem function(ing) of coastal aquaculture sites. Our results may further guide the continuing development of a practical and generic bacterial eDNA-based environmental monitoring approach.
Microbial planktonic communities are the basis of food webs in aquatic ecosystems since they contribute substantially to primary production and nutrient recycling. Network analyses of DNA metabarcoding data sets emerged as a powerful tool to untangle the complex ecological relationships among the key players in food webs. In this study, we evaluated co-occurrence networks constructed from time-series metabarcoding data sets (12 months, biweekly sampling) of protistan plankton communities in surface layers (epilimnion) and bottom waters (hypolimnion) of two temperate deep lakes, Lake Mondsee (Austria) and Lake Zurich (Switzerland). Lake Zurich plankton communities were less tightly connected, more fragmented and had a higher susceptibility to a species extinction scenario compared to Lake Mondsee communities. We interpret these results as a lower robustness of Lake Zurich protistan plankton to environmental stressors, especially stressors resulting from climate change. In all networks, the phylum Ciliophora contributed the highest number of nodes, among them several in key positions of the networks. Associations in ciliate-specific subnetworks resembled autecological species-specific traits that indicate adaptions to specific environmental conditions. We demonstrate the strength of co-occurrence network analyses to deepen our understanding of plankton community dynamics in lakes and indicate biotic relationships, which resulted in new hypotheses that may guide future research in climate-stressed ecosystems.