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Ciliated microeukaryotes (ciliates) are distinguished by their cilia, which are rich in tubulin. We developed a method for tubulin staining in ciliate cells that involves using live-cell tubulin-staining dyes instead of antibodies thereby streamlining the staining process, which is effective across diverse ciliate lineages. Moreover, our method allows integration with immunofluorescence staining using antibodies when needed. The potential applications of this technique extend to cell biology and ciliate morphological and ecological studies. [ABSTRACT FROM AUTHOR]

Vorticella convallaria are microscopic sessile suspension feeders that live attached to substrates in aquatic environments. They feed using a self‐generated current and help maintain the health of aquatic ecosystems and wastewater treatment facilities by consuming bacteria and detritus. Their environmental impact is mediated by their feeding rate. In ambient flow, feeding rates are highly dependent on an individual's orientation relative to the substrate and the flow. Here, we investigate how this orientation is impacted by flow speed. Furthermore, we examined whether individuals actively avoid orientations unfavorable for feeding. We exposed individuals to unidirectional laminar flow at shear rates of 0, 0.5, 1.0, and 1.5 s−1, and recorded their 3D orientation using a custom biplanar microscope. We determined that V. convallaria orientation became progressively tilted downstream as the shear rate increased, but individuals were still able to actively reorient. Additionally, at higher shear rates, individuals spent a larger fraction of their time in orientations with reduced feeding rates. Our shear rates correspond to freestream flows on the scale of mm s−1 to cm s−1 in natural environments. [ABSTRACT FROM AUTHOR]

Coastal and estuarine protists are frequently exposed to salinity undulation. While the tolerance and stress responses of microalgae to salinity have been extensively studied, there have been scarce studies on the physiological response of heterotrophic protists to salinity stressing. In this study, we investigated the physiological response of the heterotrophic ciliate Gastrostyla setifera to a salinity of 3, via a transcriptomic approach. The first transcriptome of genus Gastrostyla was obtained utilizing a group of manually isolated ciliate individuals (cells) and RNA-seq technique. The completeness of the transcriptome was verified. Differentially expressed gene (DEG) analysis was performed among the transcriptomes of G setifera acclimated in saline water (salinity 3) and those cultured in fresh water. The results demonstrated a significant alternation in gene transcription, in which the ciliate exhibits a transcripttomic acclimation in responding salinity stressing. The up-regulated DEGs were enriched in the pathways of cytoskeleton proteins, membrane trafficking, protein kinases and protein phosphatases. These may represent enhanced functions of ion transport, stress response and cell protections. Pathways involved in energy metabolism and biosynthesis were markedly down-regulated, reflecting decreased cell activity. Particularly, we detected significantly down-regulated genes involved in several pathways of amino acid catabolism, which may lead to accumulation of amino acids in the ciliate cell. Amino acid could act as compatible solutes in the cytoplasm to maintain the osmotic balance in saline water. Overall, this work is an initial exploration to the molecular basis of the heterotrophic protist responding to salinity stressing. The result sheds light on the mechanisms of enhancement of cell protection, reduction of cell activity, and osmotic pressure regulation in ciliates acclimated to salinity. [ABSTRACT FROM AUTHOR]

Abstract Background Hosts, parasites, and microbiota interact with each other, forming a complex ecosystem. Alterations to the microbial structure have been observed in various enteric parasitic infections (e.g. parasitic protists and helminths). Interestingly, some parasites are associated with healthy gut microbiota linked to the intestinal eubiosis state. So the changes in bacteria and metabolites induced by parasite infection may offer benefits to the host, including protection from other parasitesand promotion of intestinal health. The only ciliate known to inhabit the hindgut of grass carp, Balantidium ctenopharyngodoni, does not cause obvious damage to the intestinal mucosa. To date, its impact on intestinal microbiota composition remains unknown. In this study, we investigated the microbial composition in the hindgut of grass carp infected with B. ctenopharyngodoni, as well as the changes of metabolites in intestinal contents resulting from infection. Results Colonization by B. ctenopharyngodoni was associated with an increase in bacterial diversity, a higher relative abundance of Clostridium, and a lower abundance of Enterobacteriaceae. The family Aeromonadaceae and the genus Citrobacter had significantly lower relative abundance in infected fish. Additionally, grass carp infected with B. ctenopharyngodoni exhibited a significant increase in creatine content in the hindgut. This suggested that the presence of B. ctenopharyngodoni may improve intestinal health through changes in microbiota and metabolites. Conclusions We found that grass carp infected with B. ctenopharyngodoni exhibit a healthy microbiota with an increased bacterial diversity. The results suggested that B. ctenopharyngodoni reshaped the composition of hindgut microbiota similarly to other protists with low pathogenicity. The shifts in the microbiota and metabolites during the colonization and proliferation of B. ctenopharyngodoni indicated that it may provide positive effects in the hindgut of grass carp.

Ciliates assemble numerous microtubular structures into complex cortical patterns. During ciliate division, the pattern is duplicated by intracellular segmentation that produces a tandem of daughter cells. In Tetrahymena thermophila, the induction and positioning of the division boundary involves two mutually antagonistic factors: posterior CdaA (cyclin E) and anterior CdaI (Hippo kinase). Here, we characterized the related cdaH-1 allele, which confers a pleiotropic patterning phenotype including an absence of the division boundary and an anterior-posterior mispositioning of the new oral apparatus. CdaH is a Fused or Stk36 kinase ortholog that localizes to multiple sites that correlate with the effects of its loss, including the division boundary and the new oral apparatus. CdaH acts downstream of CdaA to induce the division boundary and drives asymmetric cytokinesis at the tip of the posterior daughter. CdaH both maintains the anterior-posterior position of the new oral apparatus and interacts with CdaI to pattern ciliary rows within the oral apparatus. Thus, CdaH acts at multiple scales, from induction and positioning of structures on the cell-wide polarity axis to local organelle-level patterning. [ABSTRACT FROM AUTHOR]

Endosymbiosis is a widespread and important phenomenon requiring diverse model systems. Ciliates are a widespread group of protists that often form symbioses with diverse microorganisms. Endosymbioses between the ciliate Euplotes and heritable bacterial symbionts are common in nature, and four essential symbionts were described: Polynucleobacter necessarius, “Candidatus Protistobacter heckmanni,” “Ca. Devosia symbiotica,” and “Ca. Devosia euplotis.” Among them, only the genus Polynucleobacter comprises very close free-living and symbiotic representatives, which makes it an excellent model for investigating symbiont replacements and recent symbioses. In this article, we characterized a novel endosymbiont inhabiting the cytoplasm of Euplotes octocarinatus and found that it is a close relative of the free-living bacterium Fluviibacter phosphoraccumulans (Betaproteobacteria and Rhodocyclales). We present the complete genome sequence and annotation of the symbiotic Fluviibacter. Comparative analyses indicate that the genome of symbiotic Fluviibacter is small in size and rich in pseudogenes when compared with free-living strains, which seems to fit the prediction for recently established endosymbionts undergoing genome erosion. Further comparative analysis revealed reduced metabolic capacities in symbiotic Fluviibacter, which implies that the symbiont relies on the host Euplotes for carbon sources, organic nitrogen and sulfur, and some cofactors. We also estimated substitution rates between symbiotic and free-living Fluviibacter pairs for 233 genes; the results showed that symbiotic Fluviibacter displays higher dN/dS mean value than free-living relatives, which suggested that genetic drift is the main driving force behind molecular evolution in endosymbionts. IMPORTANCE In the long history of symbiosis research, most studies focused mainly on organelles or bacteria within multicellular hosts. The single-celled protists receive little attention despite harboring an immense diversity of symbiotic associations with bacteria and archaea. One subgroup of the ciliate Euplotes species is strictly dependent on essential symbionts for survival and has emerged as a valuable model for understanding symbiont replacements and recent symbioses. However, almost all of our knowledge about the evolution and functions of Euplotes symbioses comes from the Euplotes– Polynucleobacter system. In this article, we report a novel essential symbiont, which also has very close free-living relatives. Genome analysis indicated that it is a recently established endosymbiont undergoing genome erosion and relies on the Euplotes host for many essential molecules. Our results provide support for the notion that essential symbionts of the ciliate Euplotes evolve from free-living progenitors in the natural water environment. [ABSTRACT FROM AUTHOR]

Unicellular ciliates like Tetrahymena are best known as free-living bacteriovores, but many species are facultative or obligate parasites. These "histophages" feed on the tissues of hosts ranging from planarian flatworms to commercially important fish and the larvae of imperiled freshwater mussels. Here, we developed a novel bioinformatics pipeline incorporating the nonstandard ciliate genetic code and used it to search for Ciliophora sequences in 34 publicly available Platyhelminthes EST libraries. From 2,615,036 screened ESTs, we identified nearly 6,000 high-confidence ciliate transcripts, supporting parasitism of seven additional flatworm species. We also cultured and identified Tetrahymena from nine terrestrial and freshwater planarians, including invasive earthworm predators from the genus Bipalium and the widely studied regeneration models Dugesia japonica and Schmidtea mediterranea. A co-phylogenetic reconstruction provides strong evidence for the coevolution of histophagous Ciliophora with their Platyhelminthes hosts. We further report the antiprotozoal aminoglycoside paromomycin expels Tetrahymena from S. mediterranea , providing new opportunities to investigate the effects of this relationship on planarian biology. Together, our findings raise the possibility that invasive flatworms constitute a novel dispersal mechanism for Tetrahymena parasites and position the Platyhelminthes as an ideal model phylum for studying the ecology and evolution of histophagous ciliates. [ABSTRACT FROM AUTHOR]

The genus Blepharisma (Alveolata, Ciliophora) is a unicellular organism distributed worldwide, even in extreme environments, and comprises numerous species. While usually proliferating through cell division, Blepharisma undergoes sexual reproduction (conjugation) when cells are moderately starved. Conjugation is initiated by mating pheromones (gamone 1 and gamone 2) secreted by complementary mating-type cells. Gamone 1, a glycoprotein, functions in a species-specific manner, while gamone 2, an amino acid derivative, is a common molecule across species. The specific function of gamone 1 suggests the possibility that mutations in gamone 1 might have led to reproductive isolation during the evolutionary process, triggering species diversification. In this study, by comparing the amino acid sequences of gamone 1 homologs from 15 strains (representing five species), we found that mutations resulting in distinct amino acid properties occur across species boundaries and are mainly concentrated at two specific regions within gamone 1. These mutations potentially alter the binding affinity of gamone 1 to its receptors, suggesting their effect in causing reproductive isolation. The interspecies artificial conjugation conducted previously and the molecular phylogenetic tree constructed using the gamone 1 homolog sequences in this study provide insights into the speciation process within the genus Blepharisma. [ABSTRACT FROM AUTHOR]

Background: Hosts, parasites, and microbiota interact with each other, forming a complex ecosystem. Alterations to the microbial structure have been observed in various enteric parasitic infections (e.g. parasitic protists and helminths). Interestingly, some parasites are associated with healthy gut microbiota linked to the intestinal eubiosis state. So the changes in bacteria and metabolites induced by parasite infection may offer benefits to the host, including protection from other parasitesand promotion of intestinal health. The only ciliate known to inhabit the hindgut of grass carp, Balantidium ctenopharyngodoni, does not cause obvious damage to the intestinal mucosa. To date, its impact on intestinal microbiota composition remains unknown. In this study, we investigated the microbial composition in the hindgut of grass carp infected with B. ctenopharyngodoni, as well as the changes of metabolites in intestinal contents resulting from infection. Results: Colonization by B. ctenopharyngodoni was associated with an increase in bacterial diversity, a higher relative abundance of Clostridium, and a lower abundance of Enterobacteriaceae. The family Aeromonadaceae and the genus Citrobacter had significantly lower relative abundance in infected fish. Additionally, grass carp infected with B. ctenopharyngodoni exhibited a significant increase in creatine content in the hindgut. This suggested that the presence of B. ctenopharyngodoni may improve intestinal health through changes in microbiota and metabolites. Conclusions: We found that grass carp infected with B. ctenopharyngodoni exhibit a healthy microbiota with an increased bacterial diversity. The results suggested that B. ctenopharyngodoni reshaped the composition of hindgut microbiota similarly to other protists with low pathogenicity. The shifts in the microbiota and metabolites during the colonization and proliferation of B. ctenopharyngodoni indicated that it may provide positive effects in the hindgut of grass carp. [ABSTRACT FROM AUTHOR]

Tintinnids (Ciliophora) are important microzooplankton grazers. In the Southern Ocean, they are found in the Antarctic Zone, Polar Front and Subantarctic Zone. The Antarctic Zone encompasses large gyres (Weddell Gyre and Ross Gyre) and the Antarctic Slope Current around the continent. The influence of these water masses on tintinnid communities has not been studied. This study investigated the tintinnid community structure in the Weddell and Cosmonaut seas in the summer of 2022. In the Weddell Gyre, tintinnid abundance was significantly lower in the interior than at the fronts. The dominant species differed between the east and west fronts: the proportion of Codonellopsis gaussi was high at the west front, whilst Laackmanniella naviculaefera, Salpingella sp. and Salpingella faurei showed high abundances at the east front. Tintinnid communities varied from inshore to offshore of the Cosmonaut Sea, possibly because of the influence from the Antarctic Slope Current and Antarctic Circumpolar Current. The Antarctic Slope Current was characterized by the occurrence of Cymatocylis drygalskii, whilst the Antarctic Circumpolar Current was characterized by Codonellopsis glacialis, Cymatocylis convallaria and Cy. calyciformis. We proposed that Cy. drygalskii can be used as an indicator of the Antarctic Slope Current. Moreover, we classify polymorphic C. gaussi into three types, in accordance with their loricae, and report their distribution characteristics in water masses. Our results contribute to a better understanding of tintinnid horizontal distribution in different parts of the Weddell Gyre and water masses and serve as a baseline for future studies of pelagic community responses to climate change in the Southern Ocean.

The subclass Cyrtophoria is a group of morphologically specialized ciliates with diverse characteristics, which can be found in a variety of aquatic and terrestrial habitats. In the present study, two cyrtophorian ciliates, Aegyria oliva Claparède & Lachmann, 1859 and A. peculiaris sp. nov., isolated from coastal waters of China, were investigated based on microscopic observations of live and protargol-stained specimens, and SSU rRNA gene sequence analyses. For A. oliva, the type species of the genus, detailed morphometric data, and improved diagnosis are provided. The new species, Aegyria peculiaris sp. nov. is characterized by a body size of 70–115 × 30–65 μm in vivo, an inverted oval body shape with a protrusion at the anterior left and a posterior bulge on the dorsal side, 45–58 somatic kineties, 31–46 nematodesmal rods, 4–6 transpodial segments, and about six contractile vacuoles. Phylogenetic analyses unveiled a close relationship between the newly identified species and A. foissneri, thereby confirming the monophyly of the genus Aegyria. [ABSTRACT FROM AUTHOR]

Serine(S)/threonine(T)-glutamine(Q) cluster domains (SCDs), polyglutamine (polyQ) tracts and polyglutamine/asparagine (polyQ/N) tracts are Q-rich motifs found in many proteins. SCDs often are intrinsically disordered regions that mediate protein phosphorylation and protein-protein interactions. PolyQ and polyQ/N tracts are structurally flexible sequences that trigger protein aggregation. We report that due to their high percentages of STQ or STQN amino acid content, four SCDs and three prion-causing Q/N-rich motifs of yeast proteins possess autonomous protein expression-enhancing activities. Since these Q-rich motifs can endow proteins with structural and functional plasticity, we suggest that they represent useful toolkits for evolutionary novelty. Comparative Gene Ontology (GO) analyses of the near-complete proteomes of 26 representative model eukaryotes reveal that Q-rich motifs prevail in proteins involved in specialized biological processes, including Saccharomyces cerevisiae RNA-mediated transposition and pseudohyphal growth, Candida albicans filamentous growth, ciliate peptidyl-glutamic acid modification and microtubule-based movement, Tetrahymena thermophila xylan catabolism and meiosis, Dictyostelium discoideum development and sexual cycles, Plasmodium falciparum infection, and the nervous systems of Drosophila melanogaster, Mus musculus and Homo sapiens. We also show that Q-rich-motif proteins are expanded massively in 10 ciliates with reassigned TAAQ and TAGQ codons. Notably, the usage frequency of CAGQ is much lower in ciliates with reassigned TAAQ and TAGQ codons than in organisms with expanded and unstable Q runs (e.g. D. melanogaster and H. sapiens), indicating that the use of noncanonical stop codons in ciliates may have coevolved with codon usage biases to avoid triplet repeat disorders mediated by CAG/GTC replication slippage.

Phyllosphere microbiota play an important role in shaping plant health and function but most research has focused only on bacterial and fungal communities. As a result, little is known about the composition of diverse microeukaryotes in the phyllosphere, including protist predators and algae, or how they are affected by host species or cooccurring bacteria. Using universal eukaryotic primers and a peptide nucleic acid clamp to block amplification of the plant 18S ribosomal RNA gene, we profiled the phyllosphere and rhizosphere microbiomes of five solanaceous crop species grown in a field plot in Connecticut, United States. Phyllosphere communities of protists, like those of bacteria, were far less diverse and more variable than those of the rhizosphere. Phyllosphere samples contained hundreds of protist sequence variants from at least seven major eukaryotic lineages, of which one-fifth were not observed in bulk soil or rhizosphere samples. Phyllosphere samples were highly enriched for a few specific sequence variants representing green algae (Chlorophyta order Chlamydomonales) and ciliates (Ciliophora class Colpodea), while rhizospheres were dominated by protists from the phylum Cercozoa. Correlation analysis identified Sphingomonas spp. bacteria as central network hubs positively associated with protists in the phyllosphere and rhizosphere. These findings indicate that, although leaf surfaces host a highly variable protist community of limited diversity, certain ciliates and green algae may be well adapted for the phyllosphere habitat.

Temporal variations in the primary production of the size-fractionated autotrophic plankton community were studied in coastal-estuarine waters of the eutrophic Gulf of Riga, Baltic Sea. The community was net-autotrophic during spring and summer and net-heterotrophic during autumn. The results of the present study clearly demonstrate strong covariation between net primary production (NPP) and

We sampled the respiratory mucus from voluntary blowhole exhalations (“blow”) of three healthy beluga whales (Delphinapterus leucas) under professional human care. Blow samples were collected from three resident belugas, one adult male (M1) and two adult females (F1, F2), with voluntary behaviors via non-invasive methods over three days in July 2021 (four days for M1). Samples were weighed and examined microscopically for the enumeration of eukaryotic and prokaryotic microbes, and then were used to evaluate carbon substrate use and taxonomic diversity of prokaryotic communities in the host respiratory sytem. Microscopical observations and 18S rRNA gene sequencing indicated the presence of eukaryotic microbiota, the ciliate genera Planilamina and Kyaroikeus in all three individuals. Exposure of samples to different metabolic carbon substrates indicated significant differences in the number of carbon sources usable by the prokaryotic communities of different whales (range: 11-25 sources), as well as a signficantly decreased diversity of carbon sources used by the community in the habitat water (5 sources). Sequencing of the hypervariable V4 region of the 16S rRNA gene revealed 19 amplicon sequence variants (ASVs) that were present in all whale samples. The oldest female D. leucas (F2) had the lowest overall diversity, and was significantly different from M1 and F1 in taxon composition, including an anomalously low ratio of Baccillota: Bacteroidota (0.01) compared to the other whales. In comparisons of microbial community composition, M1 had a significantly higher diversity than F1 and F2. These results suggest that attention should be given to regular microbiome sampling, and indicate a need for the pairing of microbiome and clinical data for animals in aquaria. Overall, these data contribute to the growing database on the core respiratory microbiota in cohabiting cetaceans under professional human care, indicate the utility of non-invasive sampling, and help characterize a baseline for healthy D. leucas.

ATP-binding cassette subfamily B (ABCB) has been implicated in various essential functions such as multidrug resistance, auxin transport and heavy metal tolerance in animals and plants. However, the functions, the genomic distribution and the evolutionary history have not been characterized systematically in lower eukaryotes. As a lineage of highly specialized unicellular eukaryotes, ciliates have extremely diverse genomic features including nuclear dimorphism. To further understand the genomic structure and evolutionary history of this gene family, we investigated the ABCB gene subfamily in 11 ciliates. The results demonstrate that there is evidence of substantial gene duplication, which has occurred by different mechanisms in different species. These gene duplicates show consistent purifying selection, suggesting functional constraint, in all but one species, where positive selection may be acting to generate novel function. We also compare the gene structures in the micronuclear and macronuclear genomes and find no gene scrambling during genome rearrangement, despite the abundance of such scrambling in two of our focal species. These results lay the foundation for future analyses of the function of these genes and the mechanisms responsible for their evolution across diverse eukaryotic lineages.

The genus Blepharisma (Alveolata, Ciliophora) is a unicellular organism distributed worldwide, even in extreme environments, and comprises numerous species. While usually proliferating through cell division, Blepharisma undergoes sexual reproduction (conjugation) when cells are moderately starved. Conjugation is initiated by mating pheromones (gamone 1 and gamone 2) secreted by complementary mating-type cells. Gamone 1, a glycoprotein, functions in a species-specific manner, while gamone 2, an amino acid derivative, is a common molecule across species. The specific function of gamone 1 suggests the possibility that mutations in gamone 1 might have led to reproductive isolation during the evolutionary process, triggering species diversification. In this study, by comparing the amino acid sequences of gamone 1 homologs from 15 strains (representing five species), we found that mutations resulting in distinct amino acid properties occur across species boundaries and are mainly concentrated at two specific regions within gamone 1. These mutations potentially alter the binding affinity of gamone 1 to its receptors, suggesting their effect in causing reproductive isolation. The interspecies artificial conjugation conducted previously and the molecular phylogenetic tree constructed using the gamone 1 homolog sequences in this study provide insights into the speciation process within the genus Blepharisma.

Protozoal infections are a world-wide problem. The toxicity and somewhat low effectiveness of the existing drugs require the search for new ways of protozoa suppression. Snake venom contains structurally diverse components manifesting antiprotozoal activity; for example, those in cobra venom are cytotoxins. In this work, we aimed to characterize a novel antiprotozoal component(s) in the Bungarus multicinctus krait venom using the ciliate Tetrahymena pyriformis as a model organism. To determine the toxicity of the substances under study, surviving ciliates were registered automatically by an original BioLaT-3.2 instrument. The krait venom was separated by three-step liquid chromatography and the toxicity of the obtained fractions against T. pyriformis was analyzed. As a result, 21 kDa protein toxic to Tetrahymena was isolated and its amino acid sequence was determined by MALDI TOF MS and high-resolution mass spectrometry. It was found that antiprotozoal activity was manifested by β-bungarotoxin (β-Bgt) differing from the known toxins by two amino acid residues. Inactivation of β-Bgt phospholipolytic activity with p-bromophenacyl bromide did not change its antiprotozoal activity. Thus, this is the first demonstration of the antiprotozoal activity of β-Bgt, which is shown to be independent of its phospholipolytic activity. [ABSTRACT FROM AUTHOR]

This review provides background and perspective for the articles contributing to the Special Issue of MDPI Micro-organisms on Paramecium as a Modern Model Organism. The six articles cover a variety of topics, each taking advantage of an important aspect of Paramecium biology: peripheral surface proteins that are developmentally regulated, endosymbiont algae and bacteria, ion channel regulation by calmodulin, regulation of cell mating reactivity and senescence, and the introns that dwell in the large genome. Each article highlights a significant aspect of Paramecium and its versatility. [ABSTRACT FROM AUTHOR]

In recent decades, sustainable forest management has been increasingly recognized, promoting the diffusion of silvicultural practices aimed at considering all components of the forest system. Deadwood is an important component of the forest ecosystem. It plays a fundamental role in providing nutrients and habitats for a wide variety of saprotrophic and heterotrophic organisms and significantly contributes to soil formation and carbon storage. Deadwood is inhabited by a plethora of organisms from various kingdoms that have evolved the ability to utilize decaying organic matter. This community, consisting of both eukaryotic and prokaryotic species, can be defined as “necrobiome”. Through the interactions between its various members, the necrobiome influences the decay rates of deadwood and plays a crucial role in the balance between organic matter decomposition, carbon sequestration, and gas exchanges (e.g., CO2) with the atmosphere. The present work aims to provide an overview of the biodiversity and role of the microbial communities that inhabit deadwood and their possible involvement in greenhouse gas (CO2, N2O, and CH4) emissions.

The mortality rate of red-tide dinoflagellates owing to predation is a major parameter that affects their population dynamics. The dinoflagellates Ansanella granifera and Ansanella sp. occasionally cause red tides. To understand the interactions between common heterotrophic protists and A. granifera, we explored the feeding occurrence of nine heterotrophic protists on A. granifera and the growth and ingestion rates of the heterotrophic dinoflagellate Gyrodinium dominans on A. granifera as a function of prey concentration and those of Oxyrrhis marina at a single high prey concentration. The heterotrophic dinoflagellates Aduncodinium glandula, G. dominans, Gyrodinium moestrupii, Luciella masanensis, Oblea rotunda, O. marina, Polykrikos kofoidii, and Pfiesteria piscicida and the naked ciliate Strombidium sp. were able to feed on A. granifera. With increasing mean prey concentrations, the growth and ingestion rates of G. dominans feeding on A. granifera rapidly increased and became saturated or slowly increased. The maximum growth and ingestion rates of G. dominans on A. granifera were 0.305 d-1 and 0.42 ng C predator-1 d-1 (3.8 cells predator-1 d-1), respectively. Furthermore, the growth and ingestion rates of O. marina on A. granifera at 1,700 ng C mL-1 (15,454 cells mL-1) were 0.037 d-1 and 0.19 ng C predator-1 d-1 (1.7 cells predator-1 d-1), respectively. The growth and ingestion rates of G. dominans and O. marina feeding on A. granifera were almost the lowest among those on the dinoflagellate prey species. Therefore, G. dominans and O. marina may prefer A. granifera less than other dinoflagellate prey species. The low mortality rate of A. granifera may positively affect its bloom formation. [ABSTRACT FROM AUTHOR]

Our knowledge of ciliate endosymbiont diversity greatly expanded over the past decades due to the development of characterization methods for uncultivable bacteria. Chlamydia‐like bacteria have been described as symbionts of free‐living amoebae and other phylogenetically diverse eukaryotic hosts. In the present work, a systematic survey of the bacterial diversity associated with the ciliate Euplotes octocarinatus strain Zam5b‐1 was performed, using metagenomic screening as well as classical full‐cycle rRNA approach, and a novel chlamydial symbiont was characterized. The metagenomic screening revealed 16S rRNA gene sequences from Polynucleobacter necessarius, three previously reported accessory symbionts, and a novel chlamydia‐like bacterium. Following the full‐cycle rRNA approach, we obtained the full‐length 16S rRNA gene sequence of this chlamydia‐like bacterium and developed probes for diagnostic fluorescence in situ hybridizations. The phylogenetic analysis of the 16S rRNA gene sequences unambiguously places the new bacterium in the family Rhabdochlamydiaceae. This is the first report of chlamydia‐like bacterium being found in Euplotes. Based on the obtained data, the bacterium is proposed as a new candidate genus and species: "Candidatus Euplotechlamydia quinta." [ABSTRACT FROM AUTHOR]

In recent decades, sustainable forest management has been increasingly recognized, promoting the diffusion of silvicultural practices aimed at considering all components of the forest system. Deadwood is an important component of the forest ecosystem. It plays a fundamental role in providing nutrients and habitats for a wide variety of saprotrophic and heterotrophic organisms and significantly contributes to soil formation and carbon storage. Deadwood is inhabited by a plethora of organisms from various kingdoms that have evolved the ability to utilize decaying organic matter. This community, consisting of both eukaryotic and prokaryotic species, can be defined as "necrobiome". Through the interactions between its various members, the necrobiome influences the decay rates of deadwood and plays a crucial role in the balance between organic matter decomposition, carbon sequestration, and gas exchanges (e.g., CO2) with the atmosphere. The present work aims to provide an overview of the biodiversity and role of the microbial communities that inhabit deadwood and their possible involvement in greenhouse gas (CO2, N2O, and CH4) emissions. [ABSTRACT FROM AUTHOR]

G protein-coupled receptors (GPCRs) are the largest family of transmembrane receptors and play important roles in many physiological processes. As a representative group of protozoa, ciliates represent the highest stage of eukaryotic cell differentiation and evolution in terms of their reproductive mode, two-state karyotype, and extremely diverse cytogenesis patterns. GPCRs have been poorly reported in ciliates. In this study, we identified 492 GPCRs in 24 ciliates. Using the existing classification system for animals, GPCRs in ciliates can be assigned to four families, including families A, B, E, and F. Most (377 members) belong to family A. The number of GPCRs is extremely different in different ciliates; the Heterotrichea ciliates usually have more GPCRs than other ciliates. Parasitic or symbiotic ciliates usually have only a few GPCRs. Gene/genome duplication events seem to play important roles in the expansion of the GPCR superfamily in ciliates. GPCRs in ciliates displayed seven typical domain organizations. GPCRs in an ortholog group are common and conserved in all ciliates. The gene expression analysis of the members in this conserved ortholog group in the model ciliate, Tetrahymena thermophila, suggested that these GPCRs play important roles in the life cycle of ciliates. In summary, this study provides the first comprehensive genome-wide identification of GPCRs in ciliates, improving our understanding of the evolution and function of GPCR in ciliates. [ABSTRACT FROM AUTHOR]

Most eukaryotes employ a combination of transcriptional and post-transcriptional silencing mechanisms to suppress transposons, yet ciliates employ a more extreme approach. They separate germline and somatic functions into distinct nuclei, enabling the elimination of transposons from the active somatic genome through diverse small RNA-mediated genome rearrangement pathways during sexual processes. [ABSTRACT FROM AUTHOR]

Nuclear dimorphism is a fundamental feature of ciliated protozoa, which have separate somatic and germline genomes in two distinct organelles within a single cell. The transcriptionally active somatic genome, contained within the physically larger macronucleus, is both structurally and functionally different from the silent germline genome housed in the smaller micronucleus. This difference in genome architecture is particularly exaggerated in Oxytricha trifallax, in which the somatic genome comprises tens of thousands of gene-sized nanochromosomes maintained at a high and variable ploidy, while the germline has a diploid set of megabase-scale chromosomes. To examine the compositional differences between the nuclear structures housing the genomes, we performed a proteomic survey of both types of nuclei and of macronuclear histones using quantitative mass spectrometry. We note distinct differences between the somatic and germline nuclei, with many functional proteins being highly enriched in one of the two nuclei. To validate our conclusions and the efficacy of nuclear separation, we used protein localization through a combination of transformations and immunofluorescence. We also note that the macronuclear histones strikingly display only activating marks, consistent with the conclusion that the macronucleus is the hub of transcription. These observations suggest that the compartmentalization of different genome features into separate structures has been accompanied by a similar specialization of nuclear components that maintain and facilitate the functions of the genomes specific to each nucleus. [ABSTRACT FROM AUTHOR]

Resting cyst formation is a crucial process of cryptobiosis in protists. In colpodid ciliates, cyst formation is accompanied by largescale morphological changes such as changes of cell shape, resorption of cilia, and formation of a cyst wall; additionally, the cell cycle is arrested. These changes provide acquired tolerance against environmental stresses. During cyst formation, mitochondrial membrane potential is reduced and the level of the ATP synthase beta chain is suppressed, strongly indicating that metabolism has ceased. Here, however, we show that ATP levels are elevated during the initial phases of encystment implying that metabolism may not be completely suppressed. This finding suggests another aspect of resting cyst formation that is not applicable to cryptobiosis. [ABSTRACT FROM AUTHOR]

Periphytic ciliates play a vital role in the material cycle and energy flow of microbial food web, however, their taxonomy and biodiversity are inadequately studied given their high species richness. Two new and one little known species, viz. Derouxella lembodes gen. et sp. nov., Cyrtophoron multivacuolatum sp. nov., and Cyrtophoron apsheronica Aliev, 1991, collected from coastal waters of China, were investigated using modern methods. Derouxella gen. nov. can be recognized by having dorsoventrally flattened body, a podite, one fragmented preoral kinety, two parallel circumoral kineties, and somatic kineties progressively shortened from right to left. Morphological classification and phylogenetic analyses based on nuclear small subunit ribosomal RNA (nSSU rRNA) and mitochondrial small subunit ribosomal RNA (mtSSU rRNA) gene sequence data inferred that Derouxella gen. nov. occupies an intermediate position between Hartmannulidae and Dysteriidae. Cyrtophoron multivacuolatum sp. nov. is characterized by large body size, the numbers of somatic kineties and nematodesmal rods, and having numerous contractile vacuoles. The genus Cyrtophoron and the poorly known species C. apsheronica were redefined. Even with the addition of newly obtained nSSU rRNA and mtSSU rRNA gene sequences of Cyrtophoron, the family Chlamydodontidae was still recovered as a monophyletic group, the monophyly of Cyrtophoron was supported too. [ABSTRACT FROM AUTHOR]

The protistan genus Epistylis contains freshwater colonial species that attach to aquatic organisms in an epibiotic or parasitic relationship. They are known to attach to the epidermis and shells of aquatic turtles, but have not been reported to cause heavy infestations or morbidity in turtles. We documented heavy infestations of Epistylis spp. in several populations of Sonoran mud turtles (Kinosternon sonoriense) inhabiting livestock ponds in Arizona, USA, and rough-footed mud turtles (Kinosternon hirtipes) from livestock ponds in Texas, USA, over the course of several years. Severe Epistylis spp. infestations on mud turtles appeared to alter diving and swimming behavior when compared to uninfested conspecifics. Infestations were cleared in captivity using tap water or a 10% salt solution, and the turtles had no permanent damage to their shell or epidermis upon clearing. While several of the mud turtles we observed had poor body condition, it is possible that the severe infestations we observed were caused by a comorbidity associated with a pathogen, parasite, or poor habitat quality that made the turtles more susceptible to the Epistylis spp. infestation. Further research on causes for these severe infestations are warranted because they contribute to changes in behavior of the heavily infested turtles and may contribute to morbidity in Kinosternon spp. when mud turtles inhabit extremely warm, shallow, eutrophic aquatic habitats, such as livestock ponds. [ABSTRACT FROM AUTHOR]

In the genus Blepharisma, reproductive isolation between different species appears to be established at least by two barriers: (1) a mating pheromone, i.e., gamone 1, and (2) a factor involved in pair formation. Using four species, we experimentally investigated other potential barriers to interspecific conjugation in Blepharisma, as well as the first and second barriers. Cell-free fluid from type I cells (CFF1) of B. americanum had no effect on B. undulans, B. japonicum, or B. stoltei. Type II cells of B. americanum responded to CFF1 from B. americanum but not to CFF1 from B. undulans, B. japonicum, or B. stoltei. Gamone 1, therefore, seems to be the first reproductive barrier (with the inclusion of B. americanum species [megakaryotype 3]) as reported previously. In pretreated cells with complementary gamones in B. undulans and B. americanum, inter-species pair formation was rare, but pair formation between B. americanum and B. japonicum and between B. americanum and B. stoltei occurred at relatively high frequency. Most of the inter-species B. americanum–B. stoltei pairs underwent nuclear changes specific to conjugation. No significant difference was observed between the intra- and inter-species pairs over the time course of the nuclear changes, but the percentage of abnormal cells was higher in inter-species pairs than in intra-species pairs, and no progenies were produced by inter-species pairs. These results suggest a third barrier or step, in addition to the first and second ones, in nuclear changes after pair formation that prevents interspecific conjugation in Blepharisma. [ABSTRACT FROM AUTHOR]

Parasite conservation is important for the maintenance of ecosystem diversity and function. Conserving parasites relies first on understanding parasite biodiversity and second on estimating the extinction risk to that biodiversity. Although steps have been taken independently in both these areas, previous studies have overwhelmingly focused on helminths in vertebrate hosts over broad scales, providing low resolution and excluding a large proportion of possible host and parasite diversity. We estimated both total obligate parasite richness and parasite extinction risk in freshwater mussels (Unionidae and Margaritiferidae) from Europe and the United States to provide a case study for considering parasite conservation in a severely understudied system. We used currently reported host–parasite relationships to extrapolate parasite diversity to all possible mussel hosts and then used the threat levels of those hosts to estimate the extinction risk for both described and undescribed parasites. An estimated 67% of parasite richness in freshwater mussels is undescribed and over 80% of the most host‐specific groups (digenean trematodes and ciliates) are undescribed. We estimated that 21% of this total parasite fauna is at immediate risk of extinction, corresponding to 60 unique species, many of which will likely go extinct before being described. Given the important roles parasites play in community structure and function and the strong ecosystem engineering capacities of freshwater mussels, such extinctions are likely to severely affect freshwater ecosystems. Our detailed study of mussel parasites provides compelling evidence for the hidden conservation threat to parasites through extinction cascades and shows parasites are deserving of immediate attention. Article Impact Statement: Two‐thirds of freshwater mussel parasites are undescribed and over one‐fifth are at immediate risk of extinction. [ABSTRACT FROM AUTHOR]

The purpose of this study is to determine which taxonomic methods can elucidate clear and quantifiable differences between two cryptic ciliate species, and to test the utility of genome architecture as a new diagnostic character in the discrimination of otherwise indistinguishable taxa. Two cryptic tintinnid ciliates, Schmidingerella arcuata and Schmidingerella meunieri, are compared via traditional taxonomic characters including lorica morphometrics, ribosomal RNA (rRNA) gene barcodes and ecophysiological traits. In addition, single‐cell 'omics analyses (single‐cell transcriptomics and genomics) are used to elucidate and compare patterns of micronuclear genome architecture between the congeners. The results include a highly similar lorica that is larger in S. meunieri, a 0%–0.5% difference in rRNA gene barcodes, two different and nine indistinguishable growth responses among 11 prey treatments, and distinct patterns of micronuclear genomic architecture for genes detected in both ciliates. Together, these results indicate that while minor differences exist between S. arcuata and S. meunieri in common indices of taxonomic identification (i.e., lorica morphology, DNA barcode sequences and ecophysiology), differences exist in their genomic architecture, which suggests potential genetic incompatibility. Different patterns of micronuclear architecture in genes shared by both isolates also enable the design of species‐specific primers, which are used in this study as unique "architectural barcodes" to demonstrate the co‐occurrence of both ciliates in samples collected from a NW Atlantic estuary. These results support the utility of genomic architecture as a tool in species delineation, especially in ciliates that are cryptic or otherwise difficult to differentiate using traditional methods of identification. [ABSTRACT FROM AUTHOR]

Heavily melanized gills in crustaceans, often referred to as black gill, have been reported in both wild and cultured marine species. Tissue melanization is generally the result of a response of the crustacean innate immune system to the presence of an irritant or pathogen. While black gill can be caused by a variety of abiotic stressors and nutritional deficiencies, biotic agents are the cause of most reported black gill cases in crustaceans. In high density culture systems, fungi are identified as the most common causes of black gill outbreaks. In the wild, epidemic-scale outbreaks of black gill appear largely to be caused by ciliate rather than fungal infections. Black gill epidemics caused by ciliates have recently been reported in two commercially important fishery species including penaeid shrimp in the South Atlantic Bight USA (Western North Atlantic) and the Gulf of Mexico, and in pandalid shrimp in the Gulf of Maine, USA. Here we review the reports of the occurrence, causative agents, biology, ecology, and impacts of black gill on wild crustacean species of black gill with special focus on the pandalid shrimp species Pandalus borealis parasitized by the apostome ciliate Synophrya sp. and penaeid shrimp in the Western North Atlantic and Gulf of Mexico parasitized by a newly described apostome ciliate species Hyalophysa lynni. A review of the literature reveals large knowledge gaps with respect to black gill in both commercially exploited and other keystone crustacean species. Recommendations for future research include improved surveillance and identification of causative agents of black gill, improved understanding of their interactions with crustacean hosts including distribution, transmission, morbidity, and mortality, epidemiology, molecular biology, and relationship with climate. [ABSTRACT FROM AUTHOR]

Calcium (Ca2+) is a universal second messenger that plays a key role in cellular signaling. However, Ca2+ signals are transduced with the help of Ca2+-binding proteins, which serve as sensors, transducers, and elicitors. Among the collection of these Ca2+-binding proteins, calmodulin (CaM) emerged as the prototypical model in eukaryotic cells. This is a small protein that binds four Ca2+ ions and whose functions are multiple, controlling many essential aspects of cell physiology. CaM is universally distributed in eukaryotes, from multicellular organisms, such as human and land plants, to unicellular microorganisms, such as yeasts and ciliates. Here, we review most of the information gathered on CaM in Paramecium, a group of ciliates. We condense the information here by mentioning that mature Paramecium CaM is a 148 amino acid-long protein codified by a single gene, as in other eukaryotic microorganisms. In these ciliates, the protein is notoriously localized and regulates cilia function and can stimulate the activity of some enzymes. When Paramecium CaM is mutated, cells show flawed locomotion and/or exocytosis. We further widen this and additional information in the text, focusing on genomic data. [ABSTRACT FROM AUTHOR]

Objective:This study aims to provide comparative information on the rumen ciliate fauna of goat (Capra aegagrus hircus) and sheep (Ovis aries) living in Zawiya, Libya.Methods:We obtained rumen samples from 16 goats and 17 sheep after the slaughter in Zawiya, Libya between June and August 2016. We immediately fixed the well-mixed samples with an equal volume of 18.5% formalin. We filtered and stained the samples in the laboratory with methyl green formalin saline solution to determine the nuclei and added 2% Lugol’s iodine solution to visualize the skeletal plates.Results:We found that the mean number (± standard deviation) of ciliates in the rumen contents from goats and sheep was 70.9±61.6×104 cells mL-1 (minimum-maximum value, 4.0-187.0×104 cells mL-1) and 96.3±49.3×104 cells mL-1 (minimum-maximum value, 19.5-235.0×104 cells mL-1), respectively. Results also showed that the total number of species per goat and sheep was 1-17 (mean, 8.2±4.7) and 1-13 (mean, 7.9±3.8), respectively. We identified 10 genera, 19 species, and 11 morphotypes in goats and 9 genera, 16 species, and 13 morphotypes in sheep. Additionally, we found that Entodinium simulans prevalence in all goats and sheep was 100%. On the other hand, we observed Hsiungia triciliata and Ostracodinium gracile in only one goat (6.3% prevalence) and Polyplastron multivesiculatum in only one sheep (5.9% prevalence). Overall, the ruminal ciliate fauna of goat and sheep in Libya comprised Entodinium species (mean for goats, 85.9%; mean for sheep, 83.5%).Conclusion:This study recorded Hsiungia triciliata as a new endosymbiont in goats. To our knowledge, this study is the first to report all of the species detected in goats from Libya. Similarly, this is the first to detect Diplodinium anisacanthum, Entodinium bursa, E. ellipsoideum, E. longinucleatum, E. simulans, Isotricha prostoma, Ophryoscolex caudatus, Ostracodinium gracile, and Polyplastron multivesiculatum in sheep from Libya.

Abstract Background Ciliated protists are a widely distributed, morphologically diverse, and genetically heterogeneous group of unicellular organisms, usually known for containing two types of nuclei: a transcribed polyploid macronucleus involved in gene expression and a silent diploid micronucleus responsible for transmission of genetic material during sexual reproduction and generation of the macronucleus. Although studies in a few species of culturable ciliated protists have revealed the highly dynamic nature of replicative and recombination events relating the micronucleus to the macronucleus, the broader understanding of the genomic diversity of ciliated protists, as well as their phylogenetic relationships and metabolic potential, has been hampered by the inability to culture numerous other species under laboratory conditions, as well as the presence of symbiotic bacteria and microalgae which provide a challenge for current sequencing technologies. Here, we optimized single-cell sequencing methods and associated data analyses, to effectively remove contamination by commensal bacteria, and generated high-quality genomes for a number of Euplotia species. Results We obtained eight high-quality Euplotia genomes by using single-cell genome sequencing techniques. The genomes have high genomic completeness, with sizes between 68 and 125 M and gene numbers between 14K and 25K. Through comparative genomic analysis, we found that there are a large number of gene expansion events in Euplotia genomes, and these expansions are closely related to the phenotypic evolution and specific environmental adaptations of individual species. We further found four distinct subgroups in the genus Euplotes, which exhibited considerable genetic distance and relative lack of conserved genomic syntenies. Comparative genomic analyses of Uronychia and its relatives revealed significant gene expansion associated with the ciliary movement machinery, which may be related to the unique and strong swimming ability. Conclusions We employed single-cell genomics to obtain eight ciliate genomes, characterized the underestimated genomic diversity of Euplotia, and determined the divergence time of representative species in this subclass for the first time. We also further investigated the extensive duplication events associated with speciation and environmental adaptation. This study provides a unique and valuable resource for understanding the evolutionary history and genetic diversity of ciliates.

Holotrichous ciliates, like Paramecium, swim through their aqueous environment by beating their many cilia. They can alter swimming speed and direction, which seems to have mesmerized early microscopists of the 1600s. We know from extensive and elegant physiological studies and generation of mutants that these cells can be considered little swimming neurons because their ciliary beating is under bioelectric control of ion channels in the cilia. This chapter will focus on the ionic control of swimming behavior by ciliary ion channels, primarily in the holotrichous ciliate Paramecium. Voltage‐gated and calcium‐activated channels for calcium, magnesium, sodium, and potassium are regulated in a closely orchestrated manner that allows cilia to bend and propel the cell forward or backward. Sensory input that generates receptor potentials feeds into the control of this channel activity and allows the cell to turn or speed up. This in turn helps the cell to avoid predators or toxic conditions. While the focus is on P. tetraurelia and P. caudatum, the principles of ciliary ion channel activity and control are easily extendable to other ciliates and protists. The high conservation of channel and ion pump structures also extends the lessons from Paramecium to higher organisms. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Ciliates are defined by the presence of dimorphic nuclei as they have both a somatic macronucleus and germline micronucleus within each individual cell. The size and structure of both germline micronuclei and somatic macronuclei vary tremendously among ciliates. Except just after conjugation (i.e. the nuclear exchange in their life cycle), the germline micronucleus is transcriptionally inactive and contains canonical chromosomes that will be inherited between generations. In contrast, the transcriptionally active macronucleus contains chromosomes that vary in size in different classes of ciliates, with some lineages having extensively fragmented gene‐sized somatic chromosomes while others contain longer multigene chromosomes. Here, we describe the variation in somatic macronuclear architecture in lineages sampled across the ciliate tree of life, specifically focusing on lineages with extensively fragmented chromosomes (e.g. the classes Phyllopharyngea and Spirotrichea). Further, we synthesize information from the literature on the development of ciliate macronuclei, focusing on changes in nuclear architecture throughout life cycles. These data highlight the tremendous diversity among ciliate nuclear cycles, extend our understanding of patterns of genome evolution, and provide insight into different germline and somatic nuclear features (e.g. nuclear structure and development) among eukaryotes. [ABSTRACT FROM AUTHOR]

Mobile genetic elements (MGEs) are transient genetic material that can move either within a single organism's genome or between individuals or species. While historically considered "junk" DNA (i.e., deleterious or at best neutral), more recent studies reveal the potential adaptive advantages MGEs provide in lineages across the tree of life. Ciliates, a group of single‐celled microbial eukaryotes characterized by nuclear dimorphism, exemplify how epigenetic influences from MGEs shape genome architecture and patterns of molecular evolution. Ciliate nuclear dimorphism may have evolved as a response to transposon invasion and ciliates have since co‐opted transposons to carry out programmed DNA deletion. Another example of the effect of MGEs is in providing mechanisms for lateral gene transfer (LGT) from bacteria, which introduces genetic diversity and, in several cases, may drive ecological specialization in ciliates. As a third example, the integration of viral DNA, likely through transduction, provides new genetic materials and can change the way host cells defend themselves against other viral pathogens. We argue that the acquisition of MGEs through non‐Mendelian patterns of inheritance, coupled with their effects on ciliate genome architecture and persistence throughout evolutionary history, exemplify how the transmission of mobile elements should be considered a mechanism of transgenerational epigenetic inheritance. [ABSTRACT FROM AUTHOR]

The generation of efficient fluid flow is crucial for organismal development and homeostasis, sexual reproduction, and motility. Multi‐ciliated cells possess fields of motile cilia that beat in synchrony to propel fluid. Ciliary arrays are remarkably conserved in their organization and function. Ciliates have polarized multi‐ciliary arrays (MCAs) to promote fluid flow for cell motility. The ciliate cortex is decorated with hundreds of basal bodies (BB) forming linear rows along the cellʼs anterior–posterior axis. BBs scaffold and position cilia to form the organized ciliary array. Nascent BBs assemble at the base of BBs. As nascent BBs mature, they integrate into the cortical BB and cytoskeletal network and nucleate their own cilium. The organization of MCAs is balanced between cortical stability and cortical dynamism. The cortical cytoskeletal network both establishes and maintains a stable organization of the MCA in the face of mechanical forces exerted by ciliary beating. At the same time, MCA organization is plastic, such that it remodels for optimal ciliary mobility during development and in response to environmental conditions. Such plasticity promotes effective feeding and ecological behavior required for these organisms. Together, these properties allow an organism to effectively sense, adapt to, and move through its environment. [ABSTRACT FROM AUTHOR]

The propagule sizes of these green seaweeds were ca. 3-10 m. Ciliates feeding on seaweed propagules were observed even when other known foods, such as diatoms and phytoflagellates, were available. I Monostroma i propagules measure 5-10 m, swim using flagella, and settle on benthic substrates; these characteristics resemble those of the propagules of many other green seaweed species. Keywords: ciliate; coastal ecosystem; food web; green seaweed; life history; microscopic grazer; population dynamics; propagule survival EN ciliate coastal ecosystem food web green seaweed life history microscopic grazer population dynamics propagule survival 1 5 5 08/03/22 20220801 NES 220801 Seaweeds, such as green (Ulvophyceae), brown (Phaeophyceae), and red (Rhodophyta) macroalgae, are primary producers in coastal ecosystems that fix carbon and release oxygen by photosynthesis, form diverse habitats, and provide food sources for various marine organisms, ranging from protists to vertebrates (Hurd et al., 2014). Although whether propagules of other green, brown, and red seaweeds are grazed by ciliates requires further investigation, propagule grazing by ciliates may be potentially widespread, which could explain the high propagule mortality rate. [Extracted from the article]

Dinoflagellates is one dominant group in coastal marine phytoplankton communities and, on occasion, form blooms in estuaries and coastal ecosystems. While relationships between dinoflagellate bloom dynamics and nutrients are well-studied, information regarding bloom dissipation in estuaries is limited. We studied the dissipation of dinoflagellate Polykrikos geminatum blooms in the Pearl River Estuary, South China Sea, during August of 2011 using ecological, molecular, and satellite remote sensing data. We found that the dinoflagellate bloom was associated with water temperatures of 29.2–31 °C, salinities ranging 16.4–20, and ambient water nutrient concentrations that were not limited. The abundance of the ciliate Euplotes rariseta, which feeds on P. geminatum cell debris and bacteria, functions as an indicator species of P. geminatum bloom dissipation. In situ and satellite data indicate that bloom water masses were transferred from the central to inner estuary near Shenzhen Bay, driven by continuous, strong southerly winds; at which point in time, P. geminatum blooms dissipated to a high-salinity area near the estuary mouth driven by northerly winds and freshwater discharge, whereupon the blooms rapidly vanished. A low tolerance to low or high salinities resulted in P. geminatum bloom demise in the Pearl River Estuary. We propose that interactions among salinity, wind, and freshwater incursion result in P. geminatum bloom dissipation in the Pearl River Estuary. [ABSTRACT FROM AUTHOR]

Ciliates are unique in having nuclear dimorphism (i.e., possessing both a germline micronucleus and a somatic macronucleus in one cell), and undergo dramatic changes during their sexual process (known as conjugation). Here we investigate the nuclear events and morphogenetic processes during conjugation in the freshwater species Euplotes aediculatus. In addition, three conjugation-related pheromone genes were sequenced and analyzed. The results indicate that: (i) the 65-hour-long conjugation process includes five nuclear divisions, i.e., three prezygotic divisions (mitosis, meiosis I and II) and two postzygotic divisions; (ii) the ciliature reorganizes twice during conjugation with the frontoventral-transverse cirral anlagen regenerating during both morphogenetic events and breaking apart in a 3:3:3:2:2 pattern; and (iii) each of three pheromone genes contains a 444 bp coding region and encodes 147 amino acid polypeptides. These results suggest a broadly shared morphogenetic pattern during conjugation in Euplotes species and provide new information for studies on the evolutionary history of pheromone genes.

Protozoal infections are a world-wide problem. The toxicity and somewhat low effectiveness of the existing drugs require the search for new ways of protozoa suppression. Snake venom contains structurally diverse components manifesting antiprotozoal activity; for example, those in cobra venom are cytotoxins. In this work, we aimed to characterize a novel antiprotozoal component(s) in the Bungarus multicinctus krait venom using the ciliate Tetrahymena pyriformis as a model organism. To determine the toxicity of the substances under study, surviving ciliates were registered automatically by an original BioLaT-3.2 instrument. The krait venom was separated by three-step liquid chromatography and the toxicity of the obtained fractions against T. pyriformis was analyzed. As a result, 21 kDa protein toxic to Tetrahymena was isolated and its amino acid sequence was determined by MALDI TOF MS and high-resolution mass spectrometry. It was found that antiprotozoal activity was manifested by β-bungarotoxin (β-Bgt) differing from the known toxins by two amino acid residues. Inactivation of β-Bgt phospholipolytic activity with p-bromophenacyl bromide did not change its antiprotozoal activity. Thus, this is the first demonstration of the antiprotozoal activity of β-Bgt, which is shown to be independent of its phospholipolytic activity.

This review provides background and perspective for the articles contributing to the Special Issue of MDPI Micro-organisms on Paramecium as a Modern Model Organism. The six articles cover a variety of topics, each taking advantage of an important aspect of Paramecium biology: peripheral surface proteins that are developmentally regulated, endosymbiont algae and bacteria, ion channel regulation by calmodulin, regulation of cell mating reactivity and senescence, and the introns that dwell in the large genome. Each article highlights a significant aspect of Paramecium and its versatility.