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Chrysophyceae are a diverse group of planktonic protists widely distributed in freshwater. They encompass a variety of orders, whereby heterotrophy has evolved independently in several phylogenetic lineages. Therefore, closely related taxa evolved that developed different feeding strategies (photo-, mixo-, heterotrophy). In high-throughput sequencing studies, the Chrysophyceae were usually addressed as a group rather than split in individual phylogenetic orders. Also because of the close relationship of the distinct nutritional strategies, no functional statements were made about nutritional patterns. Based on an extensive phylogenetic tree and phylogenetic placement, we link OTU diversity of Chrysophyceae from 218 freshwater lakes with phylogenetic affiliations. This provides information on the relative importance of lineages affiliated with different nutrition modes. Our study demonstrates that Chrysophyceae are one of the most common groups in freshwaters. We found Chrysophyceae in 213 out of 218 sample sites across Europe and in several sites they belong to the most commonly retrieved taxa. Ochromonadales and a Chrysosacca-Apoikiida clade (including Apoikiida, Chrysosaccales, Chrysastrella) are the most widespread Chrysophyceae groups and show a high degree of OTU diversity. Most detected and assignable OTUs were affiliated with mixotrophic Chrysophyceae. Niche width differs only slightly between members of different clades and between the different trophic modes. We found several OTUs within the Ochromonadales, Synurales, and Chrysosacca-Apoikiida clade, that show a wide distribution and large tolerance ranges concerning ecophysiological factors.

It is known that microorganisms are essential for the functioning of ecosystems, but the extent to which microorganisms respond to different environmental variables in their natural habitats is not clear. In the current study, we present a methodological framework to quantify the covariation of the microbial community of a habitat and environmental variables of this habitat. It is built on theoretical considerations of systems ecology, makes use of state-of-the-art machine learning techniques and can be used to identify bioindicators. We apply the framework to a data set containing operational taxonomic units (OTUs) as well as more than twenty physicochemical and geographic variables measured in a large-scale survey of European lakes. While a large part of variation (up to 61%) in many environmental variables can be explained by microbial community composition, some variables do not show significant covariation with the microbial lake community. Moreover, we have identified OTUs that act as "multitask" bioindicators, i.e., that are indicative for multiple environmental variables, and thus could be candidates for lake water monitoring schemes. Our results represent, for the first time, a quantification of the covariation of the lake microbiome and a wide array of environmental variables for lake ecosystems. Building on the results and methodology presented here, it will be possible to identify microbial taxa and processes that are essential for functioning and stability of lake ecosystems.

The term epigenetics is used for any layer of genetic information aside from the DNA base-sequence information. Mammalian epigenetic research increased our understanding of chromatin dynamics in terms of cytosine methylation and histone modification during differentiation, aging, and disease. Instead, ciliate epigenetics focused more on small RNA-mediated effects. On the one hand, these do concern the transport of RNA from parental to daughter nuclei, representing a regulated transfer of epigenetic information across generations. On the other hand, studies of Paramecium, Tetrahymena, Oxytricha, and Stylonychia revealed an almost unique function of transgenerational RNA. Rather than solely controlling chromatin dynamics, they control sexual progeny's DNA content quantitatively and qualitatively. Thus epigenetics seems to control genetics, at least genetics of the vegetative macronucleus. This combination offers ciliates, in particular, an epigenetically controlled genetic variability. This review summarizes the epigenetic mechanisms that contribute to macronuclear heterogeneity and relates these to nuclear dimorphism. This system's adaptive and evolutionary possibilities raise the critical question of whether such a system is limited to unicellular organisms or binuclear cells. We discuss here the relevance of ciliate genetics and epigenetics to multicellular organisms.

Factors shaping community patterns of microorganisms are controversially discussed. Physical and chemical factors certainly limit the survival of individual taxa and maintenance of diversity. In recent years, a contribution of geographic distance and dispersal barriers to distribution patterns of protists and bacteria has been demonstrated. Organismic interactions such as competition, predation and mutualism further modify community structure and maintenance of distinct taxa. Here, we address the relative importance of these different factors in shaping protists and bacterial communities on a European scale using high‐throughput sequencing data obtained from lentic freshwater ecosystems. We show that community patterns of protists are similar to those of bacteria. Our results indicate that cross‐domain organismic factors are important variables with a higher influence on protists as compared with bacteria. Abiotic physical and chemical factors also contributed significantly to community patterns. The contribution of these latter factors was higher for bacteria, which may reflect a stronger biogeochemical coupling. The contribution of geographical distance was similar for both microbial groups.

Dieses Kapitel umfasst Arbeitsblatter zu Themen der Evolution und Systematik fur das Bachelorstudiums und die gymnasiale Oberstufe in Anlehnung an das Lehrbuch Boenigk Biologie (2021). Eine starke Einbindung von Abbildungen in die Aufgaben unterstutzt und fordert das visuelle Lernen und somit die Festigung des gelernten Stoffs.

Microbes are essential for element cycling and ecosystem functioning. However, many questions central to understanding the role of microbes in ecology are still open. Here, we analyze the relationship between lake microbiomes and the lakes' land cover. By applying machine learning methods, we quantify the covariance between land cover categories and the microbial community composition recorded in the largest amplicon sequencing dataset of European lakes available to date. Our results show that the aggregation of environmental features or microbial taxa before analysis can obscure ecologically relevant patterns. We observe a comparatively high covariation of the lakes' microbial community with herbaceous and open spaces surrounding the lake; nevertheless, the microbial covariation with land cover categories is generally lower than the covariation with physico-chemical parameters. Combining land cover and physico-chemical bioindicators identified from the same amplicon sequencing dataset, we develop analytical data structures that facilitate insights into the ecology of the lake microbiome. Among these, a list of the environmental parameters sorted by the number of microbial bioindicators we have identified for them points towards apparent environmental drivers of the lake microbial community composition, such as the altitude, conductivity, and area covered herbaceous vegetation surrounding the lake. Furthermore, the response map, a similarity matrix calculated from the Jaccard similarity of the environmental parameters' lists of bioindicators, allows us to study the ecosystem's structure from the standpoint of the microbiome. More specifically, we identify multiple clusters of highly similar and possibly functionally linked ecological parameters, including one that highlights the importance of the calcium-bicarbonate equilibrium for lake ecology. Taken together, we demonstrate the use of machine learning approaches in studying the interplay between microbial diversity and environmental factors and introduce novel approaches to integrate environmental molecular diversity into monitoring and water quality assessments.

Species of the ciliate genus

Biogeography in Europe is known to be crucially influenced by the large mountain ranges serving as biogeographical islands for cold‐adapted taxa and geographical barriers for warm‐adapted taxa. While biogeographical patterns are well‐known for plants and animals in Europe, we here investigated diversity and distribution patterns of protist freshwater communities on a European scale (256 lakes) in the light of the well‐studied post‐glacial distribution patterns of macroorganisms. Thus, our study compared 43 alpine protist communities of lakes located in the Alps, Carpathians, Pyrenees, and the Sierra Nevada with that of surrounding lowland lakes. We verified altitudinal diversity gradients of freshwater protists with decreasing richness and diversity across altitudes similar to those observed for plants and animals. Alpine specialists and generalists could be identified differing significantly in richness and diversity, but hardly in occurrence and proportions of major taxonomic groups. High proportions of region‐specific alpine specialists indicate an increased occurrence of distinct lineages within each mountain range and thus, suggested either separated glacial refugia or post‐glacial diversification within mountain ranges. However, a few alpine specialists were shared between mountain ranges suggesting a post‐glacial recolonization from a common lowland pool. Our results identified generalists with wide distribution ranges and putatively wide tolerance ranges toward environmental conditions as main drivers of protist diversification (specification) in alpine lakes, while there was hardly any diversification in alpine specialists., Deviations of high‐mountain protist communities from lowland communities are well known but the underlying diversification processes are hardly understood. Here, we studied protist communities in several European high‐mountain ranges and analyzed commonalities and deviations between these sites. We further analyzed patterns of diversification of specialized and generalistic taxa of mountain ranges, as well as of lowlands, and showed that particularly the high mountain specialist taxa have low‐diversification rates.

Biodiversitat oder biologische Vielfalt – also die Diversitat innerhalb von Arten, zwischen Arten und zwischen Habitaten und Okosystemen – ist die Grundlage fur die Funktion, Produktivitat und Stabilitat von Okosystemen. Somit bildet sie auch die Grundlage menschlichen Lebens. Auf globaler Ebene beeinflussen vor allem die Energiezufuhr – in der Regel durch die Intensitat der Sonneneinstrahlung – sowie die klimatische und tektonische Vergangenheit die Biomasse und die Artenzahl in den verschiedenen Okoregionen der Erde. Innerhalb eines Okosystems ist die Artenvielfalt ebenfalls nicht gleichmasig verteilt, sondern durch das Einwirken abiotischer Faktoren, aber auch biotischer Interaktionen strukturiert.

Die Biologie ist eine Naturwissenschaft und beschaftigt sich folglich mit einem Phanomen, das es auch ohne das Wirken des Menschen gabe. Sie versucht, durch Beobachtungen, Messungen und Experimente moglichst grundlegende Gesetzmasigkeiten zu finden und ihre Ergebnisse mit moglichst allgemeingultigen Theorien zu erklaren.

Energie und verschiedene chemische Elemente sind fur alle Lebewesen notwendig. In offenen Systemen wie Lebewesen wird Energie stets von ausen bezogen und muss standig nachgeliefert werden. Photoautotrophe Organismen beziehen sie in Form von Sonnenstrahlung, chemolithoautotrophe Organismen beziehen Energie aus anorganischen Molekulen. Die Energie wird durch die autotrophen Organismen chemisch festgelegt bzw. in Form von ATP fur biochemische Reaktionen des Stoffwechsels bereitgestellt. Heterotrophe Lebewesen sind fur ihren Energiemetabolismus auf die Aufnahme organischer Molekule angewiesen. Als Faustregel in einem Okosystem gilt, dass nur etwa 10 % der Energie von einer trophischen Stufe zur nachsten weitergegeben werden. Ein Grosteil der verwertbaren Energie wird beispielsweise bei Atmungs-, Garungs- oder Verdauungsprozessen in Form von Warme abgegeben oder geht durch unvollstandigen Nahrungsabbau in Form von Ausscheidungen verloren.

Ziel der biologischen Systematik ist es, die Vielfalt der Organismen zu ordnen und zu benennen. Die Systematik beschaftigt sich mit der Einteilung (Taxonomie), Benennung (Nomenklatur) und Bestimmung von Lebewesen. Die Rekonstruktion der Stammesgeschichte (Phylogenie) und die Aufklarung der Prozesse und Mechanismen, die zur heutigen Vielfalt der Lebewesen fuhrten (Evolutionsbiologie), werden je nach Sichtweise als eigene Disziplinen oder als Teildisziplinen der biologischen Systematik angesehen.

Moose, Barlappe, Farne und Samenpflanzen werden als Embryophyten (Landpflanzen) zusammengefasst. Bei diesen Pflanzen wird der Sporophyt wahrend der fruhen Entwicklung als mehrzelliger Embryo von der gametophytischen Mutterpflanze ernahrt.

Rund 2 Mio. Arten wurden bisher beschrieben, der weitaus groste Teil der Biodiversitat ist aber bislang noch nicht wissenschaftlich erfasst. Die Artenvielfalt ist auf der Erde nicht gleichmasig verteilt. In den niedrigen Breiten (Tropen) ist die Artenzahl sehr hoch, in den hohen Breiten (temperate und polare Zonen) dagegen auffallig niedriger. Die Ursache fur die auffallige Haufung von Arten in den warmen Klimazonen ist nicht einfach zu erklaren, entsprechend existiert eine Vielzahl von ganz unterschiedlichen Hypothesen zur Erklarung dieser Verteilung. Diese kann in zwei Gruppen zusammenfassen: die Gleichgewichtstheorien und die Ungleichgewichtstheorien. Aussagekraftige Daten fur die globale Verteilung von Arten gibt es allerdings nur fur wenige Organismengruppen, insbesondere fur Wirbeltiere und Landpflanzen. Die meisten Organismengruppen werden, vor allem aufgrund einer mangelnden Datengrundlage, gar nicht erst in die Betrachtungen mit einbezogen – so ist unklar, ob die Hotspots der Biodiversitat von Pflanzen und Wirbeltieren auch Gebiete hoher Diversitat von Pilzen, Protisten und Prokaryoten sind.

Prokaryoten bauen auf unterschiedlichste Weise Biomasse auf und nutzen dazu verschiedene Energiequellen. Grundsatzlich lassen sich Ernahrungstypen danach einteilen, woher die Organismen die Energie und die Elektronen fur Redoxreaktionen beziehen und welche Kohlenstoffquelle sie nutzen.

Zu den wichtigsten Voraussetzungen in der Populationsgenetik zahlen sogenannte Nullmodelle, die Erwartungswerte unter neutralen Bedingungen, also ohne den Einfluss von Evolutionsfaktoren, formulieren. Mit diesen Erwartungswerten kann man beobachtete Werte vergleichen und die Abweichungen statistisch quantifizieren. Die Hardy-Weinberg-Regel, auch als Hardy-Weinberg-Gesetz bezeichnet, formuliert ein solches Nullmodell fur die Beziehung zwischen Allel- und Genotyphaufigkeiten. Es wurde zu der wohl bekanntesten populationsgenetischen Regel.

Die Vielfalt der Eukarya, insbesondere der mikrobiellen Eukarya ist riesig. Bevor man molekulare Daten fur die Aufklarung der Grosgruppensystematik nutzen konnte, wurden viele dieser Organismen als basale Tiere oder Pflanzen angesehen. In der Benennung einiger Gruppen spiegelt sich dies immer noch wider, denn fur viele Organismengruppen ist sowohl ein zoologischer als auch ein botanischer Name in Gebrauch. In verschiedenen biologischen Fachdisziplinen werden diese Organismen nach wie vor auch nach funktionellen Kriterien zu Gruppen zusammengefasst: beispielsweise bezeichnet der Begriff Protist Eukaryoten, die keine echten Gewebe bilden, umfasst also einzellige und koloniale Formen mit Ausnahme der Tiere, Pflanzen und Pilze sowie der gewebebildenden Rotalgen und Braunalgen. Als Algen werden die photosynthetisch aktiven Eukarya mit Ausnahme der Landpflanzen zusammengefasst. Diesen werden die frei lebenden heterotrophen Protisten und die parasitischen Taxa gegenubergestellt. Nach der Fortbewegungsart werden Flagellaten von Ciliaten und von Amoben unterschieden. Sowohl die verschiedenen Ernahrungsarten als auch die verschiedenen Fortbewegungsarten haben sich aber in mehreren Linien unabhangig voneinander entwickelt.

Background: Bacteria and microbial eukaryotes occupy a wide range of ecological niches and are essential for the functioning of ecosystems. The advent of next-generation sequencing methods enabled the study of environmental microbial community compositions. Yet, many questions regarding the stability and functioning of environmental microbiomes remain open. Results: In the current study, we present a methodological framework to quantify the information shared between the microbial community of a habitat and the abiotic parameters of this habitat. It is built on theoretical considerations of systems ecology and makes use of state-of-the-art machine learning techniques. It can also be used to identify bioindicators. We apply the framework to a dataset containing operational taxonomic units (OTUs) as well as more than twenty physico-chemical and geographic parameters measured in a large-scale survey of European lakes. While a large part of variation (up to 61\%) in many physico-chemical parameters can be explained by microbial community composition, some of the examined parameters only share little information with the microbiome. Moreover, we have identified OTUs that act as `multi-task’ bioindicators that could be potential candidates for lake water monitoring schemes. Conclusions: This study demonstrates the benefits of machine learning approaches in microbial ecology. Our results represent, for the first time, a quantification of information shared between the lake microbiome and a wide array of ecosystem parameters. Building on the results and methodology presented here, it will be possible to identify microbial taxa and processes central for the functioning and stability of lake ecosystems.

Lake ecosystems are hotspots on Earth for biogeochemical cycling yet linking their microbiome to physicochemical parameters remains a challenge. Here, we assess the quality of 16S rRNA gene-based metatranscriptomics, assembled metagenomics and 16S rRNA gene amplicon sequencing for 21 lake ecosystems across Europe. We identified method-dependent, massive differences between community composition and proportional activity for key taxa like Alphaproteobacteria suggesting different ecological conclusions for the same lake ecosystems. In redundancy analysis (RDA), environmental parameters explained the greatest amount of the variance in metatranscriptomes suggesting that the active community is heavily influenced by environmental parameters. While amplicon data recruited the least amount of environmental variables in RDA (pH and temperature), four additional parameters explained the sequenced metagenomes. These results suggest that metagenomes and metatranscriptomes are currently the best methods for linking lake microbiomes to physicochemical parameters and can be used as proxies for designing future ecological surveys.

Small bacterivorous eukaryotes play a cardinal role in aquatic food webs and their taxonomic classification is currently a hot topic in aquatic microbial ecology. Despite increasing interest in their diversity, core questions regarding predator–prey specificity remain largely unanswered, e.g., which heterotrophic nanoflagellates (HNFs) are the main bacterivores in freshwaters and which prokaryotes support the growth of small HNFs. To answer these questions, we fed natural communities of HNFs from Římov reservoir (Czech Republic) with five different bacterial strains of the ubiquitous betaproteobacterial genera Polynucleobacter and Limnohabitans. We combined amplicon sequencing and catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH) targeting eukaryotic 18 S rRNA genes to track specific responses of the natural HNF community to prey amendments. While amplicon sequencing provided valuable qualitative data and a basis for designing specific probes, the number of reads was insufficient to accurately quantify certain eukaryotic groups. We also applied a double-hybridization technique that allows simultaneous phylogenetic identification of both predator and prey. Our results show that community composition of HNFs is strongly dependent upon prey type. Surprisingly, Cryptophyta were the most abundant bacterivores, although this phylum has been so far assumed to be mainly autotrophic. Moreover, the growth of a small lineage of Cryptophyta (CRY1 clade) was strongly stimulated by one Limnohabitans strain in our experiment. Thus, our study is the first report that colorless Cryptophyta are major bacterivores in summer plankton samples and can play a key role in the carbon transfer from prokaryotes to higher trophic levels.

The increasing number and duration of inundations is reported to be a consequence of climate change and may severely compromise non-adapted macroorganisms. The effect of flooding events on terrestrial and aquatic microbial communities is, however, less well understood. They may respond to the changed abiotic properties of their native habitat, and the native community may change due to the introduction of alien species. We designed an experiment to investigate the effect of five different flooding durations on the terrestrial and aquatic communities of eukaryotic microorganism, using the AquaFlow mesocosms. With amplicon sequencing of the small subunit (SSU) and internal transcribed spacer (ITS) rRNA gene regions, we analyzed community compositions directly before and after flooding. Subsequently, they were monitored for another 28 days, to determine the sustainability of community changes. Our results revealed a temporary increase in similarity between terrestrial and aquatic communities according to OTU composition (operational taxonomic unit, serves as a proxy for species). Increased similarity was mainly caused by the transmission of OTUs from water to soil. A minority of these were able to persist in soil until the end of the experiment. By contrast, the vast majority of soil OTUs was not transmitted to water. Flooding duration affected the community structure (abundance) more than composition (occurrence). Terrestrial communities responded immediately to flooding and the flooding duration influenced the community changes. Independent from flooding duration, all terrestrial communities recovered largely after flooding, indicating a remarkable resilience to the applied disturbances. Aquatic communities responded immediately to the applied inundations too. At the end of the experiment, they grouped according to the applied flooding duration and the amount of ammonium and chloride that leached from the soil. This indicates a sustained long-term response of the aquatic communities to flooding events.

Chrysophytes are a diverse group of protists belonging to the Stramenopiles. They encompass a broad range of nutrition strategies (phototrophy, mixotrophy and heterotrophy) and morphological forms (unicellular, colonial, branched, non-scaled to silica-scaled). However, taxonomy, identification and delineation of genera and species are hampered by the polyphyletic origin of several morphotypes and the low resolution of morphological features; moreover, description of these features requires in many cases special equipment like TEM or SEM. To test the congruent phylogeny, genetic resolution and to reveal the genetic diversity of chrysophytes, we evaluated in this study different gene markers, in particular SSU and LSU rRNA genes, ITS, and COI in terms of phylogenetic clustering, separation of phylogenetic lineages and genetic distances within and between clades. Our results showed that the general topology of the SSU rRNA gene phylogeny is similar to that of the LSU rRNA gene phylogeny, with a higher genetic divergence for the latter. The topology of the COI phylogeny differed from the ribosomal data, and showed the highest genetic divergence within groups and between groups for all compared markers. The 5.8S rRNA gene offered only a limited phylogenetic resolution with low genetic divergence. ITS showed a high genetic divergence, but phylogenetic analyses were hampered by high variance in sequence lengths between clades.

We studied the impact of protist grazing and exudation on the growth and transcriptomic response of the prokaryotic prey species Polynucleobacter asymbioticus. Different single- and multi-species communities of chrysophytes were used to determine a species-specific response to the predators and the effect of chrysophyte diversity. We sequenced the mRNA of Pn. asymbioticus in communities with three single chrysophyte species (Chlorochromonas danica, Poterioochromonas malhamensis and Poteriospumella lacustris) and all combinations. The molecular responses of Pn. asymbioticus significantly changed in the presence of predators with different trophic modes and combinations of species. In the single-species samples we observed significant differences related to the relative importance of grazing and exudation in the protist-bacteria interaction, i.e., to the presence of either the heterotrophic Ps. lacustris or the mixotrophic C. danica. When grazing dominates the interaction, as in the presence of Ps. lacustris, genes acting in stress response are up-regulated. Further genes associated with transcription and translation are down-regulated indicating a reduced growth of Pn. asymbioticus. In contrast, when the potential use of algal exudates dominates the interaction, genes affiliated with iron transport are up-regulated. Rapid phototrophic growth of chrysophytes, with a high demand on soluble iron, could thus lead to iron-limitation and cause changes in the iron metabolism of Pn. asymbioticus. Additionally, we observe a benefit for Pn. asymbioticus from a more diverse protistan community, which could be due to shifts in the relative importance of phototrophy in the mixotrophic chrysophytes when competing for food with other species. Our study highlights the importance of biotic interactions and the specificity of such interactions, in particular the differential effect of grazing and algal exudation in the interaction of bacteria with mixotrophic protists.

OA hybrid Inferring ecosystem functioning and ecosystem services through inspections of the species inventory is a major aspect of ecological field studies. Ecosystem functions are often stable despite considerable species turnover. Using metatranscriptome analyses, we analyse a thus‐far unparalleled freshwater data set which comprises 21 mainland European freshwater lakes from the Sierra Nevada (Spain) to the Carpathian Mountains (Romania) and from northern Germany to the Apennines (Italy) and covers an altitudinal range from 38 m above sea level (a.s.l) to 3110 m a.s.l. The dominant taxa were Chlorophyta and streptophytic algae, Ciliophora, Bacillariophyta and Chrysophyta. Metatranscriptomics provided insights into differences in community composition and into functional diversity via the relative share of taxa to the overall read abundance of distinct functional genes on the ecosystem level. The dominant metabolic pathways in terms of the fraction of expressed sequences in the cDNA libraries were affiliated with primary metabolism, specifically oxidative phosphorylation, photosynthesis and the TCA cycle. Our analyses indicate that community composition is a good first proxy for the analysis of ecosystem functions. However, differential gene regulation modifies the relative importance of taxa in distinct pathways. Whereas taxon composition varies considerably between lakes, the relative importance of distinct metabolic pathways is much more stable, indicating that ecosystem functioning is buffered against shifts in community composition through a functional redundancy of taxa.

In this study, we investigated the effect of land use intensity, soil parameters and vegetation on protistan communities in grassland soils. We performed qualitative (T-RFLP) and quantitative (qPCR) analyses using primers specifically targeting the 18S rRNA gene for all Eukarya and for two common flagellate groups, i.e. the Chrysophyceae and the Kinetoplastea. Both approaches were applied to extracted soil DNA and RNA, in order to distinguish between the potentially active protists (i.e. RNA pool) and the total protistan communities, including potentially inactive and encysted cells (i.e. DNA pool). Several environmental determinants such as site, soil parameters and vegetation had an impact on the T-RFLP community profiles and the abundance of the quantified 18S rRNA genes. Correlating factors often differed between quantitative (qPCR) and qualitative (T-RFLP) approaches. For instance the Chrysophyceae/Eukarya 18S rDNA ratio as determined by qPCR correlated with the C/N ratio, whereas the community composition based on T-RLFP analysis was not affected indicating that both methods taken together provide a more complete picture of the parameters driving protist diversity. Moreover, distinct T-RFs were obtained, which could serve as potential indicators for either active organisms or environmental conditions like water content. While site was the main determinant across all investigated exploratories, land use seemed to be of minor importance for structuring protist communities. The impact of other parameters differed between the target groups, e.g. Kinetoplastea reacted on changes to water content on all sites, whereas Chrysophyceae were only affected in the Schorfheide. Finally, in most cases different responses were observed on RNA- and DNA-level, respectively. Vegetation for instance influenced the two flagellate groups only at the DNA-level across all sites. Future studies should thus include different protistan groups and also distinguish between active and inactive cells, in order to reveal causal shifts in community composition and abundance in agriculturally used systems.

Silver ions are among the predominant anthropogenic introduced pollutants in aquatic systems. As silver has effects on species at all trophic levels the community composition in aquatic habitats can be changed as a result of silver stress. The response of planktonic protists to environmental stressors is particularly important as they act both as producers and consumers in complex planktonic communities. Chrysomonad flagellates are of major interest, since this group includes heterotrophic, mixotrophic and phototrophic taxa, and therefore allows analysis of silver stress in organisms with contrasting nutritional strategies independent of a potential taxonomic bias. In a series of lab experiments, we compared the response of different trophic chrysophyte strains to low (5 μg L−1), medium (10 μg L−1) and high (20 μg L−1) nominal Ag concentrations in combination with changes in temperature and light intensity (phototrophs), temperature and food concentration (heterotrophs), or a combination of the above settings (mixotrophs). All tested strains were negatively affected by silver in their growth rates. The phototrophic strains reacted strongly to silver stress, whereas light intensity and temperature had only minor effects on growth rates. For heterotrophic strains, high food concentration toned down the effect of silver, whereas temperatures outside the growth optimum had a combined stress effect. The mixotrophic strains reacted differently depending on whether their nutritional mode was dominated by heterotrophy or by phototrophy. The precise response pattern across all variables was uniquely different for every single species we tested. The present work contributes to a deeper understanding of the effects of environmental stressors on complex planktonic communities. It indicates that silver will negatively impact planktonic communities and may create shifts in their composition and functioning.

Stream ecosystems are affected by multiple anthropogenic stressors worldwide. Even though effects of many single stressors are comparatively well studied, the effects of multiple stressors are difficult to predict. In particular bacteria and protists, which are responsible for the majority of ecosystem respiration and element flows, are infrequently studied with respect to multiple stressors responses. We conducted a stream mesocosm experiment to characterize the responses of single and multiple stressors on microbiota. Two functionally important stream habitats, leaf litter and benthic phototrophic rock biofilms, were exposed to three stressors in a full factorial design: fine sediment deposition, increased chloride concentration (salinization) and reduced flow velocity. We analyzed the microbial composition in the two habitat types of the mesocosms using an amplicon sequencing approach. Community analysis on different taxonomic levels as well as principle component analyses (PCoAs) based on realtive abundances of operational taxonomic units (OTUs) showed treatment specific shifts in the eukaryotic biofilm community. Analysis of variance (ANOVA) revealed that Bacillariophyta responded positively salinity and sediment increase, while the relative read abundance of chlorophyte taxa decreased. The combined effects of multiple stressors were mainly antagonistic. Therefore, the community composition in multiply stressed environments resembled the composition of the unstressed control community in terms of OTU occurrence and relative abundances.

Background Most protist lineages consist of members with diverging features e.g. different modes of nutrition and adaptations for life in different habitat types and climatic zones. The nutritional mode is particularly variable in chrysophytes and they are therefore an excellent model group to study the core genes and metabolic pathways of a functionally diverse lineage. The objective of our study is the identification of the joint genetic repertoire expressed in closely related chrysophytes as well as the extent of variation on species and strain level. Therefore, we investigated the transcriptomes of six strains belonging to four species of Ochromonadales. We performed analyses on metabolic pathway level as well as on sequence level. Results We could identify 1,574 core genes shared between all six investigated strains of Ochromonadales. Most of these core genes were affiliated with the primary metabolism. Phylogenetic analysis of 166 protein-coding core genes supported a close relation of Poteriospumella lacustris and Poterioochromonas malhamensis and resolved for more than 50% of investigated genes the relationship of strains affiliated with the species P. lacustris. Further, we found diverging phylogenetic patterns for genes interacting with the environment. Conclusions In Ochromonadales, a functionally diverse lineage, the core transcriptome represents only a minor part of the individual transcriptomes. But this small fraction of genes comprises the basal metabolism essential for life in several protist lineages. Phylogenetic analyses of these genes indicate a similar degree of conservation as observed for genes coding for ribosomal proteins.

Predation by microbes is one of the main drivers of bacterial mortality in the environment. In most ecosystems multiple micropredators compete at least partially for the same bacterial resource. Predatory interactions between these micropredators might lead to shifts within microbial communities. Integrating these interactions is therefore crucial for the understanding of ecosystem functioning. In this study, we investigated the predation between two groups of micropredators, i.e. phagotrophic protists and Bdellovibrio and like organisms (BALOs). BALOs are obligate predators of Gram-negative bacteria. We hypothesised that protists can prey upon BALOs despite the small size and high swimming speed of the latter, which makes them potentially hard to capture. Predation experiments including three protists, i.e. one filter feeder and two interception feeder, showed that BALOs are a relevant prey for these protists. The growth rate on BALOs differed for the respective protists. The filter feeding ciliate was growing equally well on the BALOs and on Escherichia coli, whereas the two flagellate species grew less well on the BALOs compared to E. coli. However, BALOs might not be a favourable food source in resource-rich environments as they are not enabling all protists to grow as much as on bacteria of bigger volume.

Multiple anthropogenic stressors have been shown to impact animal and plant communities in freshwater ecosystems, but the responses of aquatic fungi remain largely unknown. Stressor effects on fungal communities may, however, result in changes of decomposition of plant litter and, thus, impact nutrient cycling, a key process for ecosystem functioning. We tested the impact of increased chloride and sediment levels, as well as reduced water flow velocity, on eukaryotic freshwater communities, with an emphasis on fungi, in a mesocosm experiment. Each of the three stressors was applied individually and in all combinations in a full-factorial design. Litterbags with non-sterilised tree leaves and sterile ceramic tiles were added to the mesocosms, to analyse the responses of communities in decaying plant material and in biofilms. Fungi preferably occurring in biofilms were supposed to represent indigenous aquatic fungi, while litterbag communities should be predominantly composed of fungi known from terrestrial litter. Community composition was assessed by high-throughput sequencing of amplified barcoding regions. Similarity matrices of operational taxonomic unit (OTU) tables calculated by UCLUST and CD-HIT-OTU-Illumina were significantly correlated. Preferred occurrence in biofilm and litter communities, respectively, was used for the grouping of OTUs into three ecological guilds. Stressor sensitivity varied among the guilds. While non-fungal, in particular autotrophic, OTUs responded to several treatments, two of the fungal guilds, i.e. those exclusively colonising litter and those preferably occurring on the ceramic tiles, showed no response to any applied treatment. Only fungi preferably, but not exclusively, colonising litter significantly responded to chloride addition. Their distribution patterns again correlated significantly with those of non-fungal OTUs, indicating possible interdependencies between both groups. The results indicate that eukaryotic freshwater communities are composed of different guilds, with distinctive sensitivity and tolerance to anthropogenic stressors.