Ciliate Species Research Articles

Dynamics of digestive vacuole differentiation clarified by the observation of living Paramecium bursaria.

Paramecium bursaria is a ciliate species that has a symbiotic relationship with Chlorella spp. This study aimed to elucidate the dynamics of digestive vacuole (DV) differentiation in P. bursaria, using yeast stained with a pH indicator. Previously, DV differentiation in P. bursaria has been classified into eight periods based on fixed-cell observations. However, to understand the behavior and physiology of P. bursaria in its natural state, it is essential to observe living cells. This study presented a novel method using Cornig® Cell-Tak™ to immobilize living P. bursaria cells, which enabled long-term observation of the same cell from the same direction. This technique allowed for real-time observation of DV differentiation, including the relationship between changes in the internal pH of DV and the diameter of DV, yeast budding from the DV membrane by a single cell into the cytoplasm, and separation of a DV containing multiple yeasts into two DVs. This study provides new insights into the dynamic process of DV differentiation in P. bursaria. These findings contribute to a better understanding of the cellular mechanisms underlying the symbiotic relationship between the two organisms and shed light on the complex process of intracellular digestion in ciliates.

The phenotypic and demographic response to the combination of copper and thermal stressors strongly varies within the ciliate species, Tetrahymena thermophila.

Copper pollution can alter biological and trophic functions. Organisms can utilise different tolerance strategies, including accumulation mechanisms (intracellular vacuoles, external chelation, etc.) to maintain themselves in copper-polluted environments. Accumulation mechanisms can influence the expression of other phenotypic traits, allowing organisms to deal with copper stress. Whether copper effects on accumulation strategies interact with other environmental stressors such as temperature and how this may differ within species are still unsolved questions. Here, we tested experimentally whether the combined effect of copper and temperature modulates traits linked to demography, morphology, movement and accumulation in six strains of the ciliate Tetrahymena thermophila. We also explored whether copper accumulation might modulate environmental copper concentration effects on phenotypic and demographic traits. Results showed high intraspecific variability in the phenotypic and demographic response to copper, with interactive effects between temperature and copper. In addition, they suggested an attenuation effect of copper accumulation on the sensitivity of traits to copper, but with great variation between strains, temperatures and copper concentrations. Diversity of responses among strains and their thermal dependencies pleads for the integration of intraspecific variability and multiple stressors approaches in ecotoxicological studies, thus improving the reliability of assessments of the effects of pollutants on biodiversity.

Cancer and One Health: tumor-bearing individuals can act as super spreaders of symbionts in communities

Recent theoretical advances in the One Health approach have suggested that cancer pathologies should be given greater consideration, as cancers often render their hosts more vulnerable to infectious agents, which could turn them into super spreaders within ecosystems. Although biologically plausible, this hypothesis has not yet been validated experimentally. Using a community of cnidarians of the Hydra genus (Hydra oligactis, Hydra viridissima, Hydra vulgaris) and a commensal ciliate species (Kerona pediculus) that colonizes them, we tested whether tumoral polyps of H. oligactis, compared to healthy ones, played an amplifying role in the number of ciliates, potentially resulting in a higher likelihood of infection for other community members through spillovers. Our results indicate that K. pediculus has a higher proliferation rate on tumoral polyps of H. oligactis than on healthy ones, which results in the infestation of other hydras. However, the magnitude of the spillover differed between recipient species. This study provides to our knowledge the first elements of proof of concept that tumoral individuals in communities could act as super spreaders of symbionts within and between species, and thus affect biotic interactions and dynamics in ecosystems.

Complex evolutionary patterns within the tubulin gene family of ciliates, unicellular eukaryotes with diverse microtubular structures

BackgroundTubulins are major components of the eukaryotic cytoskeletons that are crucial in many cellular processes. Ciliated protists comprise one of the oldest eukaryotic lineages possessing cilia over their cell surface and assembling many diverse microtubular structures. As such, ciliates are excellent model organisms to clarify the origin and evolution of tubulins in the early stages of eukaryote evolution. Nonetheless, the evolutionary history of the tubulin subfamilies within and among ciliate classes is unclear.ResultsWe analyzed the evolutionary pattern of ciliate tubulin gene family based on genomes/transcriptomes of 60 species covering 10 ciliate classes. Results showed: (1) Six tubulin subfamilies (α_Tub, β_Tub, γ_Tub, δ_Tub, ε_Tub, and ζ_Tub) originated from the last eukaryotic common ancestor (LECA) were observed within ciliates. Among them, α_Tub, β_Tub, and γ_Tub were present in all ciliate species, while δ_Tub, ε_Tub, and ζ_Tub might be independently lost in some species. (2) The evolutionary history of the tubulin subfamilies varied. Evolutionary history of ciliate γ_Tub, δ_Tub, ε_Tub, and ζ_Tub showed a certain degree of consistency with the phylogeny of species after the divergence of ciliate classes, while the evolutionary history of ciliate α_Tub and β_Tub varied among different classes. (3) Ciliate α- and β-tubulin isoforms could be classified into an “ancestral group” present in LECA and a “divergent group” containing only ciliate sequences. Alveolata-specific expansion events probably occurred within the “ancestral group” of α_Tub and β_Tub. The “divergent group” might be important for ciliate morphological differentiation and wide environmental adaptability. (4) Expansion events of the tubulin gene family appeared to be consistent with whole genome duplication (WGD) events in some degree. More Paramecium-specific tubulin expansions were detected than Tetrahymena-specific ones. Compared to other Paramecium species, the Paramecium aurelia complex underwent a more recent WGD which might have experienced more tubulin expansion events.ConclusionsEvolutionary history among different tubulin gene subfamilies seemed to vary within ciliated protists. And the complex evolutionary patterns of tubulins among different ciliate classes might drive functional diversification. Our investigation provided meaningful information for understanding the evolution of tubulin gene family in the early stages of eukaryote evolution.

Micro-/nano-plastics as vectors of heavy metals and stress response of ciliates using transcriptomic and metabolomic analyses

The escalating presence of microplastics and heavy metals in marine environments significantly jeopardizes ecological stability and human health. Despite this, research on the combined effects of microplastics/nanoplastics (MPs/NPs) and heavy metals on marine organisms remains limited. This study evaluated the impact of two sizes of polystyrene beads (approximately 2 μm and 200 nm) combined with cadmium (Cd) on the ciliate species Euplotes vannus. Results demonstrated that co-exposure of MPs/NPs and Cd markedly elevated reactive oxygen species (ROS) levels in ciliates while impairing antioxidant enzyme activities, thus enhancing oxidative damage and significantly reducing carbon biomass in ciliates. Transcriptomic profiling indicated that co-exposure of MPs/NPs and Cd potentially caused severe DNA damage and protein oxidation, as evidenced by numerous differentially expressed genes (DEGs) associated with mismatch repair, DNA replication, and proteasome function. Integrated transcriptomic and metabolomic analysis revealed that DEGs and differentially accumulated metabolites (DAMs) were significantly enriched in the TCA cycle, glycolysis, tryptophan metabolism, and glutathione metabolism. This suggests that co-exposure of MPs/NPs and Cd may reduce ciliate abundance and carbon biomass by inhibiting energy metabolism and antioxidant pathways. Additionally, compared to MPs, the co-exposure of NPs and Cd exhibited more severe negative effects due to the larger specific surface area of NPs, which can carry more Cd. These findings provide novel insights into the toxic effects of MPs/NPs and heavy metals on protozoan ciliates, offering foundational data for assessing the ecological risks of heavy metals exacerbated by MPs/NPs.

Identification of Boveria labialis parasitism in the respiratory tree of the Cultured Sea cucumber, Apostichopus japonicus

Aquaculture of the sea cucumber Apostichopus japonicus has emerged as a pivotal industry in northern China in the early 21st century. It is estimated that the cultivation area for this species spans 250,356 ha, yielding an annual production of 248,508 tons. The swift growth and intensification of sea cucumber farming practices have triggered a spectrum of diseases, resulting in significant economic detriment. This study offers an exhaustive account of a particular ciliate species, identified through smear and histopathological observations, hematoxylin-eosin staining, scanning electron microscopy, and molecular biology techniques, detailing its morphology, size, cellular architecture, and reproductive mode. The ciliate exhibits a torch-like shape, measuring 40–82 μm in length and 12–35 μm in width. It is characterized by the presence of both a macronucleus and a micronucleus. The anterior end is slender and blunt, while the posterior end is the widest part of the organism. A peristomal disc (PD) is situated at the body's terminus, with the mouth positioned centrally on the PD and a lip-like projection (6–10 μm in length) extending from one side. The organism's surface, particularly the area surrounding the oral region, is adorned with an abundance of long cilia. A single contractile vacuole is observable at the aboral end of the ciliate. It possesses 17–21 somatic kineties, complemented by 3 membranelles (M1, M2, M3) and a paroral membrane (PM) within the buccal cavity. One contractile vacuole was seen at the aboral end. There were 17–21 somatic kineties, while three membranes (M1, M2, M3) and a paroral membrane (PM) located within the buccal cavity. The first somatic kinety is notably more extended than the others, uniquely reaching a length of 10 μm around the PM. The PM, comprised of 2 somatic kineties in a “zig-zag” formation, follows a spiral path, making approximately 360-degree turns in conjunction with M1, M2, and M3, and culminates at the mouth depression. The ciliate reproduces through transverse binary fission or sexual conjugation. Based on these distinguishing features and molecular biological identification results, the ciliate is provisionally classified within the genus Boveria, as Boveria labialis. Histopathological examination has shown that these ciliates are predominantly found within the respiratory trees of their hosts, where they inflict damage to the epithelial tissues. This damage manifests as cell necrosis, structural disintegration, and the shedding of cells from the respiratory tree's epithelial lining. In severe cases, the affected respiratory tree and other viscera may be expelled. Epidemiological studies have indicated that infected individuals do not present with any overt external lesions. The findings of this research are instrumental for the management of diseases and the promotion of health within the sea cucumber aquaculture industry.

Thermal response of freshwater ciliates: Can they survive at elevated lake temperatures?

Abstract Ciliates are a well‐defined, species‐rich, versatile group of heterotrophic and mixotrophic protists. Their response to increased temperature during global warming is critical for the structure and functioning of freshwater food webs. I conducted a meta‐analysis of the literature from field studies and experimental evidence to assess the parameters characterising the thermal response of freshwater ciliates. The shape of the thermal performance curve predicts the ciliates' survival at supraoptimal temperatures (i.e., the width of the thermal safety margin). The ciliates' typical thermal safety margin is c. 5°C. More than two‐thirds of the freshwater ciliates dwelling permanently or occasionally in the pelagial cannot survive at temperatures exceeding 30°C. Likewise, cold‐stenothermic species, which represent a significant fraction of euplanktonic ciliates, cannot survive by evolutionary adaptation to rapidly warming environments. The statistical analysis revealed that the ciliates' thermal performance is affected by their planktonic lifestyle (euplanktonic vs. tychoplanktonic), ability to form cysts and nutritional ecology. Bactivorous ciliates have the widest temperature niche, and algivorous ciliates have the narrowest temperature niche. Phenotypic plasticity and genetic variation, favouring the selection of pre‐adapted species in a new environment, are widespread among freshwater ciliates. However, the lack of evidence for the temperature optima and imprecisely defined tolerance limits of most species hampers the present analysis. The extent of acclimation and adaptation requires further research with more ciliate species than the few chosen thus far. Recent eco‐evolutionary experimental work and modelling approaches have demonstrated that the ciliates' thermal responses follow general trends predicted by the metabolic theory of ecology and mechanistic functions inherent in enzyme kinetics. The present analysis identified current knowledge gaps and avenues for future research that may serve as a model study for other biota. Thermal adaptation may conflict with adaptation to other stressors (predators, food availability, pH), making general predictions on the future role of freshwater ciliates in a warmer environment difficult, if not impossible, at present.

Soil water content drives the spatiotemporal the distribution and community assembly of soil ciliates in the Nianchu River Basin, Qinghai-Tibet Plateau, China.

Ciliated protozoa (ciliates) are an ecologically important group of microeukaryotes that play roles in the flow of energy and nutrients in aquatic and terrestrial ecosystems. The community distribution and diversity of soil ciliates in the Nianchu River Basin were investigated by sampling four major habitats, i.e., grassland, farmland, wetland and sea buckthorn forest during May, August and October 2020. Cultivation identification and enumeration of soil ciliates were performed by the non-submerged culture method, in vivo observations and protargol silver staining, and direct counting methods, respectively. A total of 199 species were identified representing, 89 genera, 67 families, 31 orders and 11 classes. Haptorida was the dominant group with 35 species, accounting for 17.59% of the total. The results showed that the α and β diversity indices of soil ciliate communities in the Nianchu River Basin varied significantly in spatial distribution, but not in temporal distribution. Mantel test showed that soil water content, total nitrogen and organic matter were significantly correlated with soil ciliates. Soil water content was the main environmental factor driving the spatial distribution of soil ciliates. Co-occurrence network analysis showed that soil ciliate species in the Nianchu River Basin depend on each other in the relationship of solidarity and cooperation or ecological complementarity. Thus maintaining or enhancing the diversity and stability of the community. Community assembly shows that randomness process was an important ecological process driving soil ciliate community construction in the Nianchu River Basin.

Giants' cooperation: a draft genome of the giant ciliate Muniziella cunhai suggests its ecological role in the capybara's digestive metabolism.

Several hundred ciliate species live in animals' guts as a part of their microbiome. Among them, Muniziella cunhai (Trichostomatia, Pycnotrichidae), the largest described ciliate, is found exclusively associated with Hydrochoerus hydrochaeris (capybara), the largest known rodent reaching up to 90 kg. Here, we present the sequence, structural and functional annotation of this giant microeukaryote macronuclear genome and discuss its phylogenetic placement. The 85 Mb genome is highly AT rich (GC content 25.71 %) and encodes a total of 11 397 protein-coding genes, of which 2793 could have their functions predicted with automated functional assignments. Functional annotation showed that M. cunhai can digest recalcitrant structural carbohydrates, non-structural carbohydrates, and microbial cell walls, suggesting a role in diet metabolization and in microbial population control in the capybara's intestine. Moreover, the phylogenetic placement of M. cunhai provides insights on the origins of gigantism in the subclass Trichostomatia.

The evolutionary origins and ancestral features of septins.

Septins are a family of membrane-associated cytoskeletal guanine-nucleotide binding proteins that play crucial roles in various cellular processes, such as cell division, phagocytosis, and organelle fission. Despite their importance, the evolutionary origins and ancestral function of septins remain unclear. In opisthokonts, septins form five distinct groups of orthologs, with subunits from multiple groups assembling into heteropolymers, thus supporting their diverse molecular functions. Recent studies have revealed that septins are also conserved in algae and protists, indicating an ancient origin from the last eukaryotic common ancestor. However, the phylogenetic relationships among septins across eukaryotes remained unclear. Here, we expanded the list of non-opisthokont septins, including previously unrecognized septins from glaucophyte algae. Constructing a rooted phylogenetic tree of 254 total septins, we observed a bifurcation between the major non-opisthokont and opisthokont septin clades. Within the non-opisthokont septins, we identified three major subclades: Group 6 representing chlorophyte green algae (6A mostly for species with single septins, 6B for species with multiple septins), Group 7 representing algae in chlorophytes, heterokonts, haptophytes, chrysophytes, and rhodophytes, and Group 8 representing ciliates. Glaucophyte and some ciliate septins formed orphan lineages in-between all other septins and the outgroup. Combining ancestral-sequence reconstruction and AlphaFold predictions, we tracked the structural evolution of septins across eukaryotes. In the GTPase domain, we identified a conserved GAP-like arginine finger within the G-interface of at least one septin in most algal and ciliate species. This residue is required for homodimerization of the single Chlamydomonas septin, and its loss coincided with septin duplication events in various lineages. The loss of the arginine finger is often accompanied by the emergence of the α0 helix, a known NC-interface interaction motif, potentially signifying the diversification of septin-septin interaction mechanisms from homo-dimerization to hetero-oligomerization. Lastly, we found amphipathic helices in all septin groups, suggesting that membrane binding is an ancestral trait. Coiled-coil domains were also broadly distributed, while transmembrane domains were found in some septins in Group 6A and 7. In summary, this study advances our understanding of septin distribution and phylogenetic groupings, shedding light on their ancestral features, potential function, and early evolution.

Phylogeny and species delimitation of ciliates in the genus Spirostomum (Class, Heterotrichea) using single-cell transcriptomes.

Ciliates are single-celled microbial eukaryotes that diverged from other eukaryotic lineages over a billion years ago. The extensive evolutionary timespan of ciliate has led to enormous genetic and phenotypic changes, contributing significantly to their high level of diversity. Recent analyses based on molecular data have revealed numerous cases of cryptic species complexes in different ciliate lineages, demonstrating the need for a robust approach to delimit species boundaries and elucidate phylogenetic relationships. Heterotrich ciliate species of the genus Spirostomum are abundant in freshwater and brackish environments and are commonly used as biological indicators for assessing water quality. However, some Spirostomum species are difficult to identify due to a lack of distinguishable morphological characteristics, and the existence of cryptic species in this genus remains largely unexplored. Previous phylogenetic studies have focused on only a few loci, namely the ribosomal RNA genes, alpha-tubulin, and mitochondrial CO1. In this study, we obtained single-cell transcriptome of 25 Spirostomum species populations (representing six morphospecies) sampled from South Korea and the USA, and used concatenation- and coalescent-based methods for species tree inference and delimitation. Phylogenomic analysis of 37 Spirostomum populations and 265 protein-coding genes provided a robustious insight into the evolutionary relationships among Spirostomum species and confirmed that species with moniliform and compact macronucleus each form a distinct monophyletic lineage. Furthermore, the multispecies coalescent (MSC) model suggests that there are at least nine cryptic species in the Spirostomum genus, three in S. minus , two in S. ambiguum, S. subtilis , and S. teres each. Overall, our fine sampling of closely related Spirostomum populations and wide scRNA-seq allowed us to demonstrate the hidden crypticity of species within the genus Spirostomum , and to resolve and provide much stronger support than hitherto to the phylogeny of this important ciliate genus.

Dynamics and timing of diversification events of ciliated eukaryotes from a large phylogenomic perspective

Ciliophora, an exceptionally diverse lineage of unicellular eukaryotes, exhibits a remarkable range of species richness across classes in the ciliate Tree of Life. In this study, we have acquired transcriptome and genome data from 40 representative species in seven ciliate classes. Utilizing 247 genes and 105 taxa, we devised a comprehensive phylogenomic tree for Ciliophora, encompassing over 60 % of orders and constituting the most extensive dataset of ciliate species to date. We established a robust phylogenetic framework that encompasses ambiguous taxa and the major classes within the phylum. Our findings support the monophyly of each of two subphyla (Postciliodesmatophora and Intramacronucleata), along with three subclades (Protocruzia, CONTHREEP, and SAPML) nested within Intramacronucleata, and elucidate evolutionary positions among the major classes within the phylum. Drawing on the robust ciliate Tree of Life and three constraints, we estimated the radiation of Ciliophora around 1175 Ma during the middle of the Proterozoic Eon, and most of the ciliate classes diverged from their sister lineage during the latter half of this period. Additionally, based on the time-calibrated tree and species richness pattern, we investigated net diversification rates of Ciliophora and its classes. The global net diversification rate for Ciliophora was estimated at 0.004979 species/Ma. Heterogeneity in net diversification rates was evident at the class level, with faster rates observed in Oligohymenophorea and Spirotrichea than other classes within the subclades CONTHREEP and SAPML, respectively. Notably, our analysis suggests that variations in net diversification rates, rather than clade ages, appear to contribute to the differences in species richness in Ciliophora at the class level.

Ciliate symbionts of bivalves with notes on their worldwide geographic distribution

The shells, mantle cavities and various organs of mollusks serve as suitable habitats for symbiotic ciliates, as commensal, epibiotic and parasitic. With about 80,000 species, molluscans are distributed in freshwater, marine and terrestrial habitats; symbiotic ciliates have been recorded in bivalves, gastropods and polyplacophorans; however these records have not been integrated in comprehensive revisions. The goal of this work is to provide an updated checklist of the ciliates involved as symbionts of bivalve molluscs worldwide. Available records of symbiotic species of ciliates were compiled and checked, along with their molluscan hosts and localities. We obtained data for 165 species of ciliates as symbionts of 158 bivalve hosts, distributed in 31 countries, regions and seas. This is the first comprehensive study to review the biodiversity of ciliates associated with bivalves and show that only a small fraction of this class of molluscs has been studied in terms of their symbiotic relationships with ciliates.

Genomic insights into the cellular specialization of predation in raptorial protists

BackgroundPredation is a fundamental mechanism for organisms to acquire energy, and various species have evolved diverse tools to enhance their hunting abilities. Among protozoan predators, raptorial Haptorian ciliates are particularly fascinating as they possess offensive extrusomes known as toxicysts, which are rapidly discharged upon prey contact. However, our understanding of the genetic processes and specific toxins involved in toxicyst formation and discharge is still limited.ResultsIn this study, we investigated the predation strategies and subcellular structures of seven Haptoria ciliate species and obtained their genome sequences using single-cell sequencing technology. Comparative genomic analysis revealed distinct gene duplications related to membrane transport proteins and hydrolytic enzymes in Haptoria, which play a crucial role in the production and discharge of toxicysts. Transcriptomic analysis further confirmed the abundant expression of genes related to membrane transporters and cellular toxins in Haptoria compared to Trichostomatia. Notably, polyketide synthases (PKS) and l-amino acid oxidases (LAAO) were identified as potentially toxin genes that underwent extensive duplication events in Haptoria.ConclusionsOur results shed light on the evolutionary and genomic adaptations of Haptorian ciliates for their predation strategies in evolution and provide insights into their toxic mechanisms.

Intraspecific demographic and trait responses to environmental change drivers are linked in two species of ciliate.

Over the past decade, theory and observations have suggested intraspecific variation, trait-based differences within species, as a buffer against biodiversity loss from multiple environmental changes. This buffering effect can only occur when different populations of the same species respond differently to environmental change. More specifically, variation of demographic responses fosters buffering of demography, while variation of trait responses fosters buffering of functioning. Understanding how both responses are related is important for predicting biodiversity loss and its consequences. In this study, we aimed to empirically assess whether population-level trait responses to multiple environmental change drivers are related to the demographic response to these drivers. To this end, we measured demographic and trait responses in microcosm experiments with two species of ciliated protists. For three clonal strains of each species, we measured responses to two environmental change drivers (climate change and pollution) and their combination. We also examined if relationships between demographic and trait responses existed across treatments and strains. We found different demographic responses across strains of the same species but hardly any interactive effects between the two environmental change drivers. Also, trait responses (summarized in a survival strategy index) varied among strains within a species, again with no driver interactions. Demographic and trait responses were related across all strains of both species tested in this study: Increasing intrinsic growth and self-limitation were associated with a shift in survival strategy from sit-and-wait towards flee. Our results support the existence of a link between a population's demographic and trait responses to environmental change drivers in two species of ciliate. Future work could dive deeper into the specifics of phenotypical trait values, and changes therein, related to specific life strategies in different species of ciliate and other zooplankton grazers.

Genome assembly of a symbiotic balantidia (Balantidium ctenopharyngodoni) in fish hindgut

Balantidium ctenopharyngodoni is identified as the sole ciliate species that exclusively resides within the hindgut of grass carp with high prevalence and intensity. In this study, the successful cultivation of B. ctenopharyngodoni enabled us to collect enough cells for genome sequencing. Consequently, we acquired a high-quality genome assembly spanning 68.66 Mb, encompassing a total of 22,334 nanochromosomes. Furthermore, we predicted 29,348 protein-coding genes, and 95.5% of them was supported by the RNA-seq data. The trend of GC content in the subtelomeric regions of single-gene chromosomes was similar to other ciliates containing nanochromosomes. A large number of genes encoding carbohydrate-binding modules with affinities for starch and peptidoglycans was identified. The identification of mitochondrion-related organelles (MROs) within genome indicates its well-suited adaptation to the anaerobic conditions in the hindgut environment. In summary, our results will offer resources for understanding the genetic basis and molecular adaptations of balantidia to hindgut of herbivorous fish.

Coinfection of slime feather duster worms (Annelida, Myxicola) by different gregarine apicomplexans (Selenidium) and astome ciliates reflects spatial niche partitioning and host specificity.

Individual organisms can host multiple species of parasites (or symbionts), and one species of parasite can infect different host species, creating complex interactions among multiple hosts and parasites. When multiple parasite species coexist in a host, they may compete or use strategies, such as spatial niche partitioning, to reduce competition. Here, we present a host–symbiont system with two species of Selenidium (Apicomplexa, Gregarinida) and one species of astome ciliate co-infecting two different species of slime feather duster worms (Annelida, Sabellidae, Myxicola) living in neighbouring habitats. We examined the morphology of the endosymbionts with light and scanning electron microscopy (SEM) and inferred their phylogenetic interrelationships using small subunit (SSU) rDNA sequences. In the host ‘Myxicola sp. Quadra’, we found two distinct species of Selenidium; S. cf. mesnili exclusively inhabited the foregut, and S. elongatum n. sp. inhabited the mid to hindgut, reflecting spatial niche partitioning. Selenidium elongatum n. sp. was also present in the host M. aesthetica, which harboured the astome ciliate Pennarella elegantia n. gen. et sp. Selenidium cf. mesnili and P. elegantia n. gen. et sp. were absent in the other host species, indicating host specificity. This system offers an intriguing opportunity to explore diverse aspects of host–endosymbiont interactions and competition among endosymbionts.

Spatiotemporal distribution patterns of soil ciliate communities in the middle reaches of the Yarlung Zangbo River

Introduction: Soil ciliates, as protozoa, play a crucial role in biogeochemical cycling and the soil food web, yet they are highly sensitive to environmental fluctuations in soil conditions. The diversity and biogeographic characteristics of soil ciliates in the Tibetan Plateau remain poorly understood. As part of a regional survey focused on soil ciliate diversity, we investigated the composition and spatiotemporal variations of soil ciliate communities along the Yarlung Zangbo River, a representative soil habitat in the Tibetan Plateau.Methods: A total of 290 soil samples were collected from four habitat types of grassland, shrubland, forestland and wetland in the middle reaches of the Yarlung Zangbo River during the wet and dry seasons, and 138 species of ciliates were identified.Results: Soil ciliate diversity exhibited greater variation across habitat types than seasons. Moreover, soil ciliate diversity was higher during the wet season compared to the dry season, with the wetland habitat showing the highest diversity and the grassland habitat displaying the lowest. We observed spatiotemporal heterogeneity in the composition of soil ciliate communities across different seasons and habitat types. Notably, Litostomatea, Karyorelictea, and Prostomatea predominated in ciliate communities during the wet season and in grassland habitat. Phyllopharyngers dominated during dry seasons and in forested regions, while Spirotrichea species were prevalent in wetland and forested areas. The co-occurrence network analysis showed that soil ciliate community was more complex in wet season than in dry season, and the stability of soil ciliate community in wet season was higher than that in dry season. The stability of soil ciliate community in wetland was higher than that in forestland, shrubland and grassland, and the anti-interference ability was stronger. Soil temperature (ST), Total nitrogen (TN), Soil organic matter (SOM) and Soil water content (SWC) are important factors affecting the structure of soil ciliate community. By influencing the metabolic rate and nutrient acquisition of soil ciliates, the distribution pattern of soil ciliate community diversity in the middle reaches of Yarlung Zangbo River is shaped.Discussion: In summary, this study revealed the distribution pattern of soil ciliate community diversity in the Yarlung Zangbo River Basin, and the key factors affecting the spatial and temporal differences and stability of the community, enhancing our understanding of how ciliates adapt to environmental conditions in soil habitats across the Tibetan Plateau.

Ciliate diversity in rodrigo de freitas lagoon (Rio de Janeiro, Brazil) from an integrative standpoint.

The Rodrigo de Freitas Lagoon is a highly eutrophic lacustrine system and has one of the longest histories of exploration and anthropic alteration in Brazil. Despite its relevance, limited studies explored the diversity of micro-eukaryotes in the lagoon. Ciliates (Alveolata, Ciliophora) are overlooked in environmental microbiology, especially in tropical and subtropical ecosystems, resulting in limited knowledge about their diversity and functional relevance in South American habitats, particularly in coastal lagoons. To fill this gap, here we investigated the diversity of ciliates in a brackish coastal lagoon in an urban area of Rio de Janeiro, Brazil, applying and comparing the performance of morphological and metabarcoding approaches. The metabarcoding analysis, based on high-throughput sequencing of the hipervariable region V4 of the 18S rRNA genes detected 37 molecular operational taxonomic units (MOTUs) assigned to Ciliophora, representing only about a half (56.9%) of the diversity detected by microscopy, which counted 65 ciliate morphotypes. The most representative classes in both approaches were Spirotrichea and Oligohymenophorea. The metabarcoding analysis revealed that 35.3% of the ciliate MOTUs had less than 97% similarity to available sequences in the NCBI database, indicating that more than one-third of these MOTUs potentially represents still not represented or undescribed ciliate species in current databases. Our findings indicate that metabarcoding techniques can significantly enhance the comprehension of ciliate diversity in tropical environments, but the scarcity of reference sequences of brackish ciliates in molecular databases represents a challenge to the taxonomic assignment of the MOTUs. This study provides new insights into the diversity of ciliates in a threatened coastal lagoon, revealing a vast array of still unknown and rare ciliate taxonomic units in tropical environments.

Rumen ciliates (Ciliophora, Trichostomatia) in Brazilian domestic cattle feeding on diets with crescent urea levels

Since their discovery, rumen ciliates of domestic cattle have been reported from various geographic locations. However, until now there is only one taxonomic inventory of ciliates associated with Brazilian cattle. The present study aimed to assess the community composition, relative abundance, richness, and density of rumen ciliates in Brazilian cattle, whose feeding diets were supplemented with crescent urea levels. Across all treatments analyzed, one subclass, two orders, three families, 11 genera, and 31 species of ciliates were identified. The ciliate community composition and species richness varied among the four treatments used. However, the total ciliate density was not affected by the experimental diets. We described a new entodiniid morphotype, Entodinium caudatum m. orbonuclearis, and recorded Oligoisotricha bubali for the second time in Brazil.