Genus Euplotes Research Articles

Morphology and molecular phylogeny of Euplotes baugilensis n. sp. (Ciliophora, Spirotrichea), with an illustrated key to Euplotes species with reduced cirri

Euplotes baugilensis n. sp. was discovered in a temporary puddle that formed after rainfall on a mountain footpath near Gangneung-Wonju National University in Gangneung, South Korea. After isolation, a pure culture was established, and the new species was examined using live observation, silver-impregnation (protargol and ‘wet’ silver nitrate), scanning electron microscopy, and the analysis of the 18S rRNA gene sequence. Morphologically, E. baugilensis n. sp. is characterized by small body size (on average 49 × 31 µm in vivo), 9 ordinary fronto-ventral cirri (cirrotype-9) with one reduced cirrus V/2 (composed of four non-ciliated basal bodies), 5 transverse cirri, 7 or 8 dorsolateral kineties, 6 dorsal prominent ridges, and a dargyrome (silverline system) of double type. In this study, we have used a combination of morphological and molecular techniques to characterize E. baugilensis n. sp. and determine its phylogenetic position within the genus Euplotes. Molecular analysis using 18S rRNA gene sequences indicated that E. baugilensis n. sp. is most closely related to E. curdsi (with a sequence identity of 96.8 %).

Redescription of two Euplotes species (Ciliophora, Euplotida) from Yangtze River Estuary, China, with a note on the distributions of this genus in China

Ciliates are important unicellular organisms in the studies of biomolecules, genetics, and evolution. Euplotids are a highly diversified and widely distributed group. The morphology of two euplotids, Euplotes dominicanus and E. parkei, isolated from the Yangtze River Estuary, China, were investigated based on live observation, protargol-, and Chatton-Lwoff staining methods. The Chinese population of E. dominicanus resembles the original abyssal population except for having two caudal cirri and seven dorsolateral kineties. The Chinese population of E. parkei corresponds well with the original description in size, having eight frontoventral cirri, two marginal cirri, and a double-eurystomus dorsal silverline system. The diagnoses were improved by incorporating newly obtained data, detailed illustrations, and photomicrographs were supplemented. Euplotes parkei sensu needs to be reinvestigated. Phylogenetic analyses based on SSU rRNA gene sequence data confirmed the branching position of the two taxa within the genus Euplotes. The geographical distribution of the genus Euplotes in China was also briefly reviewed, and further exploration is needed in the brackish habitat, particularly focusing on the estuary zone.

Unusual Dependence between Gene Expression and Negative Selection in Euplotes

In most of the studied organisms, gene expression is associated with a number of evolutionary features pertaining to the protein-coding sequences. In particular, gene expression positively correlates with the average intensity of negative selection and influences codon usage. Here, we study the connection between gene expression and selection patterns in two species of ciliate protists of the genus Euplotes. We find that codon usage is influenced by gene expression in these organisms, pointing at additional evolutionary constraints on mutations in heavily expressed genes relative to the genes expressed at lower rates. At the same time, at the level of synonymous vs. non-synonymous substitutions we observe a stronger constraint on the genes expressed at lower rates relative to those with higher rates of expression. Our study adds to the discussion about the general evolutionary patterns and opens new questions about the mechanisms of control of gene expression in ciliates.

Single-cell Microbiomics Unveils Distribution and Patterns of Microbial Symbioses in the Natural Environment.

Protist-bacteria associations are extremely common. Among them, those involving ciliates of the genus Euplotes are emerging as models for symbioses between prokaryotes and eukaryotes, and a great deal of information is available from cultured representatives of this system. Even so, as for most known microbial symbioses, data on natural populations is lacking, and their ecology remains largely unexplored; how well lab cultures represent actual diversity is untested. Here, we describe a survey on natural populations of Euplotes based on a single-cell microbiomic approach, focusing on taxa that include known endosymbionts of this ciliate. The results reveal an unexpected variability in symbiotic communities, with individual hosts of the same population harboring different sets of bacterial endosymbionts. Co-occurring Euplotes individuals of the same population can even have different essential symbionts, Polynucleobacter and "Candidatus Protistobacter," which might suggest that replacement events could be more frequent in nature than previously hypothesized. Accessory symbionts are even more variable: some showed a strong affinity for one host species, some for a sampling site, and two ("Candidatus Cyrtobacter" and "Candidatus Anadelfobacter") displayed an unusual pattern of competitive exclusion. These data represent the first insight into the prevalence and patterns of bacterial symbionts in natural populations of free-living protists.

The hidden genomic diversity of ciliated protists revealed by single-cell genome sequencing

BackgroundCiliated 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.ResultsWe 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.ConclusionsWe 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.

The macronuclear genome of the Antarctic psychrophilic marine ciliate Euplotes focardii reveals new insights on molecular cold adaptation

The macronuclear (MAC) genomes of ciliates belonging to the genus Euplotes species are comprised of numerous small DNA molecules, nanochromosomes, each typically encoding a single gene. These genomes are responsible for all gene expression during vegetative cell growth. Here, we report the analysis of the MAC genome from the Antarctic psychrophile Euplotes focardii. Nanochromosomes containing bacterial sequences were not found, suggesting that phenomena of horizontal gene transfer did not occur recently, even though this ciliate species has a substantial associated bacterial consortium. As in other euplotid species, E. focardii MAC genes are characterized by a high frequency of translational frameshifting. Furthermore, in order to characterize differences that may be consequent to cold adaptation and defense to oxidative stress, the main constraints of the Antarctic marine microorganisms, we compared E. focardii MAC genome with those available from mesophilic Euplotes species. We focussed mainly on the comparison of tubulin, antioxidant enzymes and heat shock protein (HSP) 70 families, molecules which possess peculiar characteristic correlated with cold adaptation in E. focardii. We found that α-tubulin genes and those encoding SODs and CATs antioxidant enzymes are more numerous than in the mesophilic Euplotes species. Furthermore, the phylogenetic trees showed that these molecules are divergent in the Antarctic species. In contrast, there are fewer hsp70 genes in E. focardii compared to mesophilic Euplotes and these genes do not respond to thermal stress but only to oxidative stress. Our results suggest that molecular adaptation to cold and oxidative stress in the Antarctic environment may not only be due to particular amino acid substitutions but also due to duplication and divergence of paralogous genes.

Microbiota associated with the large-scale outdoor cultivation of the cyanobacterium Synechococcus sp. PCC 7002

The model euryhaline cyanobacterium Synechococcus sp. PCC 7002 has potential as a platform for biotechnological applications because of its genetic amenability and fast growth rates. The purpose of this work was to measure the outdoor productivity metrics of Synechococcus sp. PCC 7002, which we tested by cultivation in 110 L flat-panel photobioreactors and 1025 L open raceway ponds at the Algae Testbed Public Private Partnership (ATP3) algae culturing testbed site at the Arizona Center for Algae Technology and Innovation (AzCATI). This work was carried out during the summer growing season when ambient temperatures and light availability are highest to support maximum photoautotrophic biomass yields. Modifications to the traditional A+ laboratory growth media for Synechococcus sp. PCC 7002 included the use of urea as a nitrogen source, and CO2 sparging for automated pH control in open ponds. Synechococcus showed robust growth in flat-panel photobioreactors, which are suited for the containment of modified organisms; however, cultivation in the open-raceway pond system was challenging due to pond crashes. We investigated the microbiota associated with Synechococcus pond cultures using Illumina amplicon sequencing of the 16S rRNA genes of bacteria and archaea and the 18S rRNA genes of microbial eukaryotes, to identify potential competitor and predator genera. These results pointed to likely predation of Synechococcus by a ciliated protozoan of the genus Euplotes. Development of crop protection strategies will be crucial for enabling the mass cultivation of Synechococcus in open pond systems.

Genome Analysis of a Verrucomicrobial Endosymbiont With a Tiny Genome Discovered in an Antarctic Lake.

Organic Lake in Antarctica is a marine-derived, cold (−13∘C), stratified (oxic-anoxic), hypersaline (>200 gl–1) system with unusual chemistry (very high levels of dimethylsulfide) that supports the growth of phylogenetically and metabolically diverse microorganisms. Symbionts are not well characterized in Antarctica. However, unicellular eukaryotes are often present in Antarctic lakes and theoretically could harbor endosymbionts. Here, we describe Candidatus Organicella extenuata, a member of the Verrucomicrobia with a highly reduced genome, recovered as a metagenome-assembled genome with genetic code 4 (UGA-to-Trp recoding) from Organic Lake. It is closely related to Candidatus Pinguicocccus supinus (163,218 bp, 205 genes), a newly described cytoplasmic endosymbiont of the freshwater ciliate Euplotes vanleeuwenhoeki (Serra et al., 2020). At 158,228 bp (encoding 194 genes), the genome of Ca. Organicella extenuata is among the smallest known bacterial genomes and similar to the genome of Ca. Pinguicoccus supinus (163,218 bp, 205 genes). Ca. Organicella extenuata retains a capacity for replication, transcription, translation, and protein-folding while lacking any capacity for the biosynthesis of amino acids or vitamins. Notably, the endosymbiont retains a capacity for fatty acid synthesis (type II) and iron–sulfur (Fe-S) cluster assembly. Metagenomic analysis of 150 new metagenomes from Organic Lake and more than 70 other Antarctic aquatic locations revealed a strong correlation in abundance between Ca. Organicella extenuata and a novel ciliate of the genus Euplotes. Like Ca. Pinguicoccus supinus, we infer that Ca. Organicella extenuata is an endosymbiont of Euplotes and hypothesize that both Ca. Organicella extenuata and Ca. Pinguicocccus supinus provide fatty acids and Fe-S clusters to their Euplotes host as the foundation of a mutualistic symbiosis. The discovery of Ca. Organicella extenuata as possessing genetic code 4 illustrates that in addition to identifying endosymbionts by sequencing known symbiotic communities and searching metagenome data using reference endosymbiont genomes, the potential exists to identify novel endosymbionts by searching for unusual coding parameters.

Systematic positions and taxonomy of two new ciliates found in China: Euplotes tuffraui sp. nov. and E. shii sp. nov. (Alveolata, Ciliophora, Euplotida)

The morphology and SSU rDNA-based phylogeny of two small marine euplotid species isolated from China, Euplotes tuffraui sp. nov. and E. shii sp. nov., were investigated. Euplotes tuffraui sp. nov. has a combination of features including body size (35–50 μm × 15–35 μm), body shape (generally triangle-shaped) adoral membranelles gradually bending at rear end, 10 frontoventral, five transverse, two caudal and two closed marginal cirri with the lower one bearing smaller basal plaques, six dorsal kineties with 1–3 and 6–11 dikinetids in leftmost and mid-dorsal kineties, respectively, and dorsal silverline system double-patella-I type. Euplotes shii sp. nov. is a small-sized form (25–35 μm × 15–25 μm) with 10 frontoventral, five transverse, one marginal and two caudal cirri; six or seven dorsal kineties with about seven dikinetids in mid-dorsal kineties and dorsal silverline system double-eurystomus type. Phylogenetic analyses based on molecular data confirmed the branching positions of these new taxa within the genus Euplotes and supported the validity of the two organisms as novel and distinct species.

Characterization of Euplotes lynni nov. spec., E. indica nov. spec. and description of E. aediculatus and E. woodruffi (Ciliophora, Euplotidae) using an integrative approach

Four species belonging to the genus Euplotes have been investigated, namely: E. lynni nov. spec., E. indica nov. spec., E. aediculatus, and E. woodruffi. All populations are from India and were investigated using morphological and molecular markers. The phylogenetic relationships were inferred from small subunit ribosomal rRNA gene (SSU rRNA), internal transcribed spacer (ITS) region, and mitochondrial cytochrome c oxidase subunit I (COI) gene. Predicted secondary structure models for two new species using the hypervariable region of the SSU rRNA gene and ITS2 region support the distinctness of both species. Morphological characters were subjected to principal component analysis (PCA) and genetic variations were studied in-depth to analyze the relatedness of the two new species with their congeners. An integrative approach combining morphological features, molecular analysis, and ecological characteristics was carried out to understand the phylogenetic position of the reported species within the different clades of the genus Euplotes.

Novel Contributions to the Taxonomy of the Ciliates Genus Euplotes (Ciliophora, Euplotida): Redescription of Two Poorly Known Species, With a Brief Note on the Distributions of This Genus in Coastal Waters of Southern China

As the typical periphytic ciliate, the genus Euplotes Ehrenberg, 1830 is highly diversified and commonly observed in marine water. In this study, the living morphology, infraciliature and silverline system of two poorly known Euplotes species, E. neapolitanusWichterman, 1964 and E. antarcticusFenchel and Lee, 1972, isolated from coastal water of southern China, were investigated. The original description of these two species were brief, and thus we provided detailed redescription based on our Chinese population. Their diagnoses were improved by adding some morphology characteristics and their detailed illustrations and photomicrographs were first supplied here. Based on the sufficient justification for identification of our population by morphology, their small subunit ribosomal RNA gene sequences which have been reported were linked to the accurate species name. Phylogenetic analyses showed that these two species cluster with their congeners which shared high morphological similarities with them. In addition, the geographic distribution of the genus Euplotes in coast of southern China was revealed, and the mangrove was considered as the ideal habitat for them by possessing the higher species richness.

Simple morphology-based species identification in Euplotes spp.

Ciliates are unicellular protists of the phylum Ciliophora and found in high abundances in water systems world-wide. Today their important ecological role in all aquatic systems is well known. However, morphological species identification in ciliates is difficult due to sometimes tiny morphological characteristics. We here present a simplified method visualizing all important species classification patterns. We focused on species identification in the genus Euplotes using immunocytochemistry and confocal laser scanning microscopy. With these tools, we identify and describe the shape of the interphase macronucleus, the number and distribution of the ventral cirri as well as the species-specific body surface tubulin pattern. We visualize and describe three species difficult to distinguish: Euplotes octocarinatus, Euplotes aediculatus and Euplotes daidaleos. Species identification was subsequently validated with the help of 18S rDNA genome sequencing. We anticipate that this method can also be applied for the identification of different ciliate species in a cost and time effective manner.

Euplotes octocarinatus Carter, 1972 (Ciliophora, Spirotrichea, Euplotidae): Considerations on its morphology, phylogeny, and biogeography

The cosmopolitan genus Euplotes Ehrenberg, 1830 comprises a highly distinguishable group of ciliates. However, details of the cell surface, the ciliature, and molecular data are still scarce for some species. We studied Euplotes octocarinatus Carter, 1972 from two Mexican freshwater bodies, providing data on its morphology, SSU rRNA gene sequence, and phylogeny. In addition, we obtained all data of previous records to show its geographic distribution and biogeographical pattern. The current populations showed some differences as compared with the original description and we provide an improved diagnosis. Morphologically, the species is very similar to Euplotes patella and E. daidaleos but differs by invariably having eight dorsolateral kineties (vs. nine in Euplotes patella and E. daidaleos), and lacking endosymbiotic green algae (vs. present in E. daidaleos). Phylogenetically, the Mexican population of E. octocarinatus nested with four isolates of the species lacking morphological characterization. The Euplotes octocarinatus described herein grouped into a fully-supported clade, which includes E. patella, E. amieti, E. daidaleos, E. eurystomus, E. woodruffi and E. aediculatus. Biogeographically, E. octocarinatus seems to have a wide distribution.

Biogeography and Character Evolution of the Ciliate Genus Euplotes (Spirotrichea, Euplotia), with Description of Euplotes curdsi sp. nov.

Ciliates comprise a diverse and ecologically important phylum of unicellular protists. One of the most specious and best-defined genera is Euplotes, which constitutes more than 70 morphospecies, many of which have never been molecularly tested. The increasing number of described Euplotes taxa emphasizes the importance for detailed characterizations of new ones, requiring standardized morphological observations, sequencing of molecular markers and careful comparison with previous literature. Here we describe Euplotes curdsi sp. nov., distinguishable by the combination of the following features: 45–65 μm length, oval or elongated shape with both ends rounded, narrow peristome with 25–34 adoral membranelles, conspicuous paroral membrane, double-eurystomus dorsal argyrome type, 6–7 dorsolateral kineties and 10 frontoventral cirri. Three populations of the novel species have been found in brackish and marine samples in the Mediterranean and the White Sea. We provide the SSU rRNA gene sequences of these populations, and an updated phylogeny of the genus Euplotes. Using the molecular phylogenetic tree, we inferred aspects of the biogeographical history of the genus and the evolution of its most important taxonomic characters in order to provide a frame for future descriptions. Ultimately, these data reveal recurrent trends of freshwater invasion and highlight the dynamic, yet convergent, morphological evolution of Euplotes.

Reclassification of four Polynucleobacter necessarius strains as representatives of Polynucleobacter asymbioticus comb. nov., Polynucleobacter duraquae sp. nov., Polynucleobacter yangtzensis sp. nov. and Polynucleobacter sinensis sp. nov., and emended description of Polynucleobacter necessarius.

Genome comparisons based on average nucleotide identity (ANI) values of four strains currently classified as Polynucleobacter necessarius subsp. asymbioticus resulted in ANI values of 75.7–78.4 %, suggesting that each of those strains represents a separate species. The species P. necessarius was proposed by Heckmann and Schmidt in 1987 to accommodate obligate endosymbionts of ciliates affiliated with the genus Euplotes. The required revision of this species is, however, hampered by the fact, that this species is based only on a description and lacks a type strain available as pure culture. Furthermore, the ciliate culture Euplotes aediculatus ATCC 30859, on which the description of the species was based, is no longer available. We found another Euplotes aediculatus culture (Ammermann) sharing the same origin with ATCC 30859 and proved the identity of the endosymbionts contained in the two cultures. A multilocus sequence comparison approach was used to estimate if the four strains currently classified as Polynucleobacter necessarius subsp. asymbioticus share ANI values with the endosymbiont in the Ammermann culture above or below the threshold for species demarcation. A significant correlation (R2 0.98, P<0.0001) between multilocus sequence similarity and ANI values of genome-sequenced strains enabled the prediction that it is highly unlikely that these four strains belong to the species P. necessarius. We propose reclassification of strains QLW-P1DMWA-1T (=DSM 18221T=CIP 109841T), MWH-MoK4T (=DSM 21495T=CIP 110977T), MWH-JaK3T (=DSM 21493T=CIP 110976T) and MWH-HuW1T (=DSM 21492T=CIP 110978T) as Polynucleobacter asymbioticus comb. nov., Polynucleobacter duraquae sp. nov., Polynucleobacter yangtzensis sp. nov. and Polynucleobacter sinensis sp. nov., respectively.

On molecular biology of ciliated protozoa: Frontier areas and progresses

Ciliated protists are important organisms which play significant roles in studies on cell biology, genetics, biodiversity, biogeography and ecology, environmental biology etc. In last decade, molecular investigations on phylogeny, barcoding, epigenetics, genomics, and gene evolution have been performed by the authors’ groups and the main results can be summarized as follows: (i) Phylogenetic relationships within over 50 classes/orders are analyzed, and two new classes, six new orders/suborders are established by the authors’ groups, based on more than 2000 new sequences. Additionally, theoretical researches focusing on gene marker selection and topological optimization are also performed, in order to provide theoretical guidance for future study. We suggested that unidentified environmental sequences, and secondary structures of rRNA gene could be used for inferring phylogenetic relationships of ciliates, at least on some taxon level. And we also discussed the impact of missing data present in concatenated analyses, and paralogs of protein-coding genes on phylogenetic analyses. (ii) Transcriptome/genome genome of six representative ciliates ( Strombidium sulcatum , Uronema marinum , Metanophrys similis , Euplotes vannus , Uroleptopsis citrina , Paramecium caudatum ) were sequenced and analyzed, which will help to find out the evolutionary position of key species, the relationship between expression of the functional gene family and morphological characteristics, and to understand the association between genetic information and phenotype; Also, we compared mitochondrial genome of the genus Euplotes species, thus found the gene order and transcriptional directions were the same among three species, but 3 split protein coding genes ( nad9 , nad2 and rpl16 ) were predicted only in mt-genome of E. vannus . (iii) Knockout of histone methyltransferase TXR1 ( Tetrahymena Trithorax related 1), specific for H3 lysine 27 mono-methylation (H3K27me1), leads to severe replication stress in the model organism Tetrahymena thermophila . Consequently, cells mobilize the DNA damage response, indicating that perturbation of epigenetic information can directly affect replication elongation. (iv) Alternative processing is extensive among gene families in Chilodonella uncinata which are likely to be C. uncinata specific; and the processing patterns are different among gene families which is more complex than previously believed. We propose a new model whereby gene scrambling evolves by gene duplication followed by partial and reciprocal degradation of the duplicate sequences. In this model, alternative processing represents an intermediate step in the evolution of scrambled genes and yields important insights into the mechanism for speciation in ciliates. (v) Four gene markers, viz. COI , ITS1, ITS2, D2 region of 28SrRNA gene, are evaluated as promising candidate barcoding markers, by comparing 8 gene makers on the same organisms for the first time. DNA barcoding sequences of 83 species covering subclass Peniculia, Oligotrichia and Euplotia are firstly sequenced. And sampling information, morphological characters and pictures of these species are also recorded for constructing DNA barcoding database of ciliates.

High frequency of +1 programmed ribosomal frameshifting in Euplotes octocarinatus.

Programmed −1 ribosomal frameshifting (−1 PRF) has been identified as a mechanism to regulate the expression of many viral genes and some cellular genes. The slippery site of −1 PRF has been well characterized, whereas the +1 PRF signal and the mechanism involved in +1 PRF remain poorly understood. Previous study confirmed that +1 PRF is required for the synthesis of protein products in several genes of ciliates from the genus Euplotes. To accurately assess the frequency of genes requiring frameshift in Euplotes, the macronuclear genome and transcriptome of Euplotes octocarinatus were analyzed in this study. A total of 3,700 +1 PRF candidate genes were identified from 32,353 transcripts, and the gene products of these putative +1 PRFs were mainly identified as protein kinases. Furthermore, we reported a putative suppressor tRNA of UAA which may provide new insights into the mechanism of +1 PRF in euplotids. For the first time, our transcriptome-wide survey of +1 PRF in E. octocarinatus provided a dataset which serves as a valuable resource for the future understanding of the mechanism underlying +1 PRF.

Monoculture of the ciliate protozoan Euplotes sp. (Ciliophora; Hypotrichia) fed with different diets

Ciliate protozoa of the genus Euplotes commonly appears contaminating mass cultures of rotifers but also with potential to be used as live food in the larviculture of marine fish. To obtain a monoculture of Euplotes sp., three diets were tested: 1) microalgae Nannochloropsis oculata, 2) commercial diet for rotifers Culture Selco 3000, and 3) baker's yeast (Saccharomyces cerevisiae). The ciliates were inoculated at 10 ind. mL - ¹. On day 5, protozoa densities in the groups fed the commercial diet (1,911.0 ± 248.7 ind. mL - ¹) and the baker's yeast (2,600.0 ± 195.3 ind. mL -1 ) did not differ, but were higher than the group fed microalgae (2.0 ± 1.4 ind. mL -1 ) (p < 0.05). On day 6, the density in the group fed baker's yeast was higher (15,484.0 ± 1,164.9 ind. mL - ¹) than in the groups fed microalgae (3.0 ± 1.4 ind. mL - ¹) or commercial diet (11,287.0 ± 1,468.0 ind. mL - ¹). An exponential growth curve was observed for the protozoa fed baker's yeast (R² = 0.992; p < 0.05) and commercial diet (R² = 0.979; p < 0.05). The microalgae diet did not result in satisfactory growth of the protozoan. Feeding baker's yeast or commercial rotifer's diet to a monoculture of Euplotes sp. can result in very high densities of this protozoan.

Diterpenoids from Marine Ciliates: Chemical Polymorphism of Euplotes rariseta

AbstractA homogeneous, though multifaceted, secondary metabolic character emerges from a detailed investigation of secondary metabolites produced by the ciliate species Euplotes rariseta. In particular, from the strain NZ2, collected in New Zealand (Omaha Bay), two new irregular diterpenoids, omaholidenol (6) and omaholidenal (7), have been isolated which are the C5 homologues of rarisetenolide (1), the latter being previously found as the main secondary metabolite in different strains of the same species. On the other hand, from strain Ubt22, three new diterpenoids, ubatubaolidenal (8), ubatubadial A (9), and ubatubadial B (10), have been found. Finally, two new diterpenoids, epoxyfocardolide (11) and prenyl epoxyrarisetenolde (12), were isolated in low yields from the sister species Euplotes quinquecarinatus and Euplotes parkei, respectively. All these findings strongly suggest, in addition to a wide chemical polymorphism in E. rariseta populations, a close parallelism between the production pattern of secondary metabolites and the phylogenetic relationships of the species, confirming the chemotaxonomic utility of these compounds in the ciliate genus Euplotes.

Betaproteobacterial symbionts of the ciliate Euplotes: origin and tangled evolutionary path of an obligate microbial association

The Polynucleobacter-Euplotes association is an obligatory symbiotic system between a monophyletic group of ciliate species belonging to the genus Euplotes and bacteria of the species Polynucleobacter necessarius (Betaproteobacteria). Both organisms are unable to survive independently. Several studies revealed the existence of free-living populations of Polynucleobacter bacteria which are phylogenetically closely related to the endosymbiotic ones, but never share associations with Euplotes in the natural environment. Hence, following the most parsimonious explanation on the origin of the association, this symbiosis should represent a synapomorphic character for the hosts' clade. Nevertheless, phylogenetic analyses performed on an increased number of strains here presented suggest that Euplotes species, during their evolution, recruited Polynucleobacter bacteria as symbionts more than once. Moreover, in three cases, we observed different bacteria as obligate symbionts. These symbionts are the first characterized representatives of a phylogenetic lineage branching in a basal position with respect to the genus Polynucleobacter. The hypothesis that the original obligate symbionts belonged to this newly discovered clade and that, only subsequently, in most cases they have been replaced by Polynucleobacter bacteria recruited from the environment is proposed and discussed. The evolutionary path of this association seems anyway to have been more complex than so far supposed.