Marine Planktonic Ciliates Research Articles

Relating ciliary propulsion morphology and flow to particle acquisition in marine planktonic ciliates I: the tintinnid ciliate Amphorides quadrilineata

Abstract The marine tintinnid ciliate Amphorides quadrilineata is a feeding-current feeder, creating flows for particle encounter, capture and rejection. Individual-level behaviors were observed using high-speed, high-magnification digital imaging. Cells beat their cilia backward to swim forward, simultaneously generating a feeding current that brings in particles. These particles are then individually captured through localized ciliary reversals. When swimming backward, cells beat their cilia forward (=ciliary reversals involving the entire ring of cilia), actively rejecting unwanted particles. Cells achieve path-averaged speeds averaging 3–4 total lengths per second. Both micro-particle image velocimetry and computational fluid dynamics were employed to characterize the cell-scale flows. Forward swimming generates a feeding current, a saddle flow vector field in front of the cell, whereas backward swimming creates an inverse saddle flow vector field behind the cell; these ciliary flows facilitate particle encounter, capture and rejection. The model-tintinnid with a full-length lorica achieves an encounter rate Q ~29% higher than that without a lorica, albeit at a ~142% increase in mechanical power and a decrease in quasi-propulsive efficiency (~0.24 vs. ~ 0.38). It is also suggested that Q can be approximated by π(W/2 + l)2U, where W, l and U represent the lorica oral diameter, ciliary length and swimming speed, respectively.

New evidence of consistency between phylogeny and morphology for two taxa in ciliated protists, the subclasses Oligotrichia and Choreotrichia (Protista, Ciliophora)

Marine planktonic ciliates are largely oligotrichs and choreotrichs, which are two subclasses of the class Spirotrichea. The current phylogenetic assignments of oligotrichs and choreotrichs are inconsistent with previous results based on morphological features, probably hindered by the limited information from a single gene locus. Here we provide 53 new sequences from small subunit ribosomal RNA (SSU rDNA), ITS1-5.8S rDNA-ITS2, and large subunit ribosomal RNA (LSU rDNA) gene loci in 25 oligotrich and choreotrich species. We also predict RNA secondary structures for the ITS2 regions in 55 species, 48 species of which are reported for the first time. Based on these novel data, we make a more comprehensive phylogenetic reconstruction, revealing consistency between morphological taxonomy and an updated phylogenetic system for oligotrichs and choreotrichs. With the addition of data from ciliature patterns and genes, the phylogenetic analysis of the subclass Oligotrichia suggests three evolutionary trajectories, among which: 1) Novistrombidium asserts an ancestral ciliary pattern in Oligotrichia; 2) the subgenera division of Novistrombidium and Parallelostrombidium are fully supported; 3) the three families (Tontoniidae, Pelagostrombidiidae and Cyrtostrombidiidae) all evolved from the most diverse family Strombidiidae, which explains why strombidiids consistently form polyphyletic clades. In the subclass Choreotrichia, Strombidinopsis likely possesses an ancestral position to other choreotrichs, and both phylogenetic analysis and RNA secondary structure prediction support the hypothesis that tintinnids may have evolved from Strombidinopsis. The results presented here offer an updated hypothesis for the evolutionary history of oligotrichs and choreotrichs based on new evidence obtained by expanding sampling of molecular information across multiple gene loci.

Growth-promoting and low-salt adaptation responses boosted by spermidine in Strombidium parasulcatum, a marine bacteriovorous ciliate potentially applied to live feeds for marine larviculture

Ciliates have been suggested as potential live food organisms for the first-feeding stage of various aquaculture animal larvae because of, among others, their wide range of body size and relatively good availability in the surrounding environment. Unfortunately, studies on the nutritional contents or large-scale cultivation methods of ciliates are relatively sparse. Here we report a novel approach to efficiently separate the spermidine-enriched bacterial feeds from marine planktonic ciliate Strombidium parasulcatum. We also report the role of spermidine (Spd) in the standard mass culture of this ciliate. Our method was able to concentrate the ciliates up to 1.22 × 105 cells/mL (approximately 12-fold higher than the normal cultivation) with a recovery rate of 63.89 ± 2.254%. Regarding the role of Spd, we have allowed the bacterial feeds to accumulate a high amount of intracellular Spd from the culture medium (4.10-fold that of the control group). The ciliates receiving Spd-enrich feed exhibited a significant increase in the growth rate (increased by 10.5% to 56.4%), cellular Spd (increased by 1.23-fold to 2.81-fold), and clearance rate (∼20% within 4 h). In terms of stress vulnerability, we observed that S. parasulcatum was still able to accumulate Spd under low-salt stress (10‰ salinity). Besides, the addition of Spd could also assist ciliates in overcoming oxidative stress. Taken together, we concluded that Spd has an important function in the cultivation of the ciliate S. parasulcatum and our novel method facilitated its mass production. Therefore, the applied concepts and findings provided in this study may serve as a baseline for the future development of S. parasulcatum as a commercial live feed.

Do marine planktonic ciliates follow Bergmann's rule?

Body size is a fundamental trait determining individual fitness and ecological processes. Reduction in body size with increasing temperature has been widely observed in most ectotherms and endotherms, known as Bergmann's rule. However, we lack data to assess if ciliates, the major consumers of marine primary production, follow Bergmann's rule and what drives the distributions of their cell size. Here, we examined a data set (287 samples) collected across the global oceans to investigate biogeographic patterns in the mean cell‐size of ciliate communities. By measuring the sizes of every ciliate cell (< 10 to > 300 per sample), we found that community cell‐size increased with increasing latitude, conforming to Bergmann's rule. We then addressed the cause. Temperature was a main driver of the trend. Ciliate community mean cell‐size decreased 34% when temperature increased from 3.5 to 31°C, implying that temperature may be a direct physiological driver. In addition, prey (phytoplankton) size also influenced the trend, with ciliate size increasing by 35% across the gradient of phytoplankton size (0.6–15.5 μm). Generally, these findings emphasized the importance of how both biotic and abiotic factors affect size distribution of marine ciliates, a key component of pelagic ecosystems. Our novel, extensive dataset and the predictive trends arising from them contribute to understanding how climate change will influence pelagic ecosystem functions.

A light and electron microscopical study on the resting cyst of the tintinnid Schmidingerella (Alveolata, Ciliophora) including a phylogeny-aware comparison

Resting cysts protect ciliates against adverse environmental conditions. The morphology and ultrastructure of resting cysts has been described in very few Oligotrichea, a group of mainly marine planktonic ciliates. The present study provides the first ultrastructural data for loricate choreotrichids, applying light and electron microscopy on the cysts of the tintinnid Schmidingerella meunieri (Kofoid and Campbell, 1929) Agatha and Strüder-Kypke, 2012. The morphology of live cysts and the wall ultrastructure of cryofixed cysts were morphometrically analysed. The resting cyst is roughly flask-shaped, broadening to a slightly concave, laterally protruding anterior plate. An emergence pore closed by a skull cap-shaped papula is directed to the bottom of the lorica on the opposite side of the cyst. The cyst wall consists of an ectocyst, mesocyst, and endocyst differing in thickness, structure, and nitrogen concentration as revealed by conventional transmission electron microscopy, electron energy loss spectroscopy, and electron spectroscopic imaging. The cysts of S. meunieri belong to the kinetosome-resorbing type, which also occurs in the majority of hypotrich ciliates. Two main features (flask-shape and presence of an emergence pore) are shared with the closely related aloricate choreotrichids and oligotrichids, distinguishing the Oligotrichea from the hypotrich and the more distantly related euplotid ciliates.

Impacts of inorganic nutrients on the physiology of a mixoplanktonic ciliate and its cryptophyte prey.

Many marine planktonic ciliates retain functional chloroplasts from their photosynthetic prey and use them to incorporate inorganic carbon via photosynthesis. While this strategy provides the ciliates with carbon, little is known about their ability to incorporate major dissolved inorganic nutrients, such as nitrogen and phosphorus. Here, we studied how ciliates respond to different concentrations of dissolved inorganic nitrogen and phosphorus. Specifically, we tested the direct and indirect effects of nutrient availability on the ciliate Strombidium cf. basimorphum fed the cryptophyte prey Teleaulax amphioxeia. We assessed responses in the rates of growth, ingestion, photosynthesis, inorganic nutrient uptake, and excretion. Our results show that the prey changed its carbon content depending on the nutrient concentrations. Low inorganic nutrient concentrations increased S. cf. basimorphum growth and prey ingestion. The higher carbon content of the prey under these low nutrient conditions likely supported the growth of the ciliate, while the higher carbon:nutrient stoichiometry of the prey led to the higher ingestion rates. The low carbon content of the prey at high nutrient concentrations resulted in reduced growth of S. cf. basimorphum, which indicates that carbon acquired via photosynthesis in the ciliate cannot compensate for the ingestion of prey with low carbon content. In conclusion, our findings show S. cf. basimorphum is not able to utilize dissolved inorganic nitrogen and phosphorus for growth, and this species seems to be well adapted to exploit its prey when grown at low nutrient conditions.

Morphological, Molecular, and Growth Characteristics of a Cryptic Species, Strombidium parasulcatum n. sp. (Alveolata: Ciliophora: Oligotrichida).

A new marine planktonic ciliate from Taiwan, Strombidium parasulcatum sp. n., is described based on live observations, protargol staining, and molecular data. Its morphological characters are similar to those of Strombidium sulcatum Claparède and Lachmann, 1859 sensu Song et al., 2000 but differ from S. sulcatum sensu Fauré-Fremiet, 1912 and sensu Fauré-Fremiet and Ganier, 1970 by several morphological characters. The 18S rRNA gene sequences of the two forms display 76 base pair differences (about 5%), indicating that they should be considered separate species. The highest observed specific growth rates of S. parasulcatum in culture were 1.79 day–1 over 1 day and 1.52 day–1 over 2 days, both starting at day 5. Bacteria appear to be an important food resource for the cultivation of this medium-sized oligotrich ciliate. This and other recent studies suggest that cryptic species may be common in the genus Strombidium, and an integrative approach including morphological, ecological, and molecular data should be used to address this question.

Genetic Diversity in Marine Planktonic Ciliates (Alveolata, Ciliophora) Suggests Distinct Geographical Patterns – Data From Chinese and European Coastal Waters

Unraveling geographic distribution patterns of planktonic protists is a central goal in marine microbial ecology. Using a novel combination of recently developed phylogenetic and network analyses on a V4 18S rDNA metabarcoding dataset, we here analyzed the genetic diversity of marine planktonic ciliate communities in Chinese and European coastal waters. Thereby, our approach provided an unprecedented perspective on geographic patterns inferred from ciliate genetic diversity and accomplished a very fine resolution down to single nucleotides within operational taxonomic units (OTUs). While most OTUs (87%) exclusively contained sequences of either Chinese or European origin, those OTUs detected in both regions comprised the vast majority of reads (84%). Phylogenetic analyses of OTUs belonging to the same taxon revealed genetically distinct clades that were geographically restricted to either Chinese or European coastal waters. The detection of signature nucleotides emphasized this genetic distinction of Chinese and European clades. Second-level clustering of OTUs and reference sequences in two selected taxa (the oligotrichid Spirotontonia and the tintinnid Tintinnidium) revealed the presence of several potentially new species or ones lacking genetic reference data. Geographic patterns were also discovered by network analyses within 700 widespread and abundant OTUs; in 77 of these OTUs, European and Chinese sequences formed significantly assortative groups. These assortative groupings indicated a higher genetic similarity among sequences from the same region than between sequences from different regions. Our results demonstrate that detailed analyses of metabarcoding data down to single nucleotide differences expand our perception of geographical distribution patterns and provide insights into historic and ongoing effective dispersal in protists. The congruent discovery of geographic patterns at different levels of resolution (between and within OTUs) suggests that cosmopolitan distribution in marine planktonic ciliates is less common than previously postulated.

Tintinnids (Ciliophora: Tintinnida) from Mexico: a checklist

The order Tintinnida comprises 14 families and includes marine, estuarine, and freshwater planktonic ciliates. The goal of this paper is to provide an updated species checklist of Mexican tintinnids for which we revised and checked all available records including some data of their distribution. We obtained the records for 203 species of tintinnids, representing 40 genera and 12 families. The genera Tintinnopsis and Eutintinnus contained the highest number of species. The vast majority of species (199) were recorded in marine habitats. The Southern Gulf of Mexico ecoregion had the highest species richness (87), although some ecoregions have not been studied.

Species check-list for Tintinnids of the Philippines Archipelago (Protozoa, Ciliophora)

Tintinnids are an essential link between nano- and macro- planktons in the food webs of the marine environment. It is also known that tintinnids are one of themajor components of marine planktonic ciliates and has a cosmopolitan character. In the Philippine archipelago, which is recognized as a center of marine biodiversity, tintinnids checklist has not been done or published. Therefore, a checklist is presented in this study based on a compilation of previous tintinnids studies conducted at the Philippines waters. As a result of the studies done since 1941 up to present, a total of 114 taxa belonging to 14 families and 37 genera were listed. The Philippines coastal waters record a total of 50 species while the open seas document 72 species to date.

The Tara Oceans voyage reveals global diversity and distribution patterns of marine planktonic ciliates.

Illumina reads of the SSU-rDNA-V9 region obtained from the circumglobal Tara Oceans expedition allow the investigation of protistan plankton diversity patterns on a global scale. We analyzed 6,137,350 V9-amplicons from ocean surface waters and the deep chlorophyll maximum, which were taxonomically assigned to the phylum Ciliophora. For open ocean samples global planktonic ciliate diversity is relatively low (ca. 1,300 observed and predicted ciliate OTUs). We found that 17% of all detected ciliate OTUs occurred in all oceanic regions under study. On average, local ciliate OTU richness represented 27% of the global ciliate OTU richness, indicating that a large proportion of ciliates is widely distributed. Yet, more than half of these OTUs shared <90% sequence similarity with reference sequences of described ciliates. While alpha-diversity measures (richness and exp(Shannon H)) are hardly affected by contemporary environmental conditions, species (OTU) turnover and community similarity (β-diversity) across taxonomic groups showed strong correlation to environmental parameters. Logistic regression models predicted significant correlations between the occurrence of specific ciliate genera and individual nutrients, the oceanic carbonate system and temperature. Planktonic ciliates displayed distinct vertical distributions relative to chlorophyll a. In contrast, the Tara Oceans dataset did not reveal any evidence that latitude is structuring ciliate communities.

Differences in the vertical distribution and response to freshwater discharge between aloricate ciliates and tintinnids in the East China Sea

Marine planktonic ciliates are important components of microzooplankton. Depending on the presence or absence of lorica, planktonic ciliates can be divided into tintinnids and aloricate ciliates. We hypothesize that the ecological distributions of the two groups were different due to their difference in morphology. To test this hypothesis, the spatial distribution of ciliates was studied in spring, summer and autumn 2011 in the East China Sea, a large marginal sea significantly affected by freshwater discharge. We found that tintinnids and aloricate ciliates had different vertical distributions. Tintinnids were distributed mainly near the bottom waters, while higher abundance of aloricate ciliate was found in waters 30–70m above the bottom. The contribution of tintinnids to the total ciliate abundance decreased with increasing distance from the bottom. In waters with distance from the bottom >80m, tintinnids accounted for <10% of the total ciliate abundance. The Changjiang River discharge in summer enhanced aloricate ciliate abundance compared with spring and autumn, although tintinnid abundance did not change significantly. Tintinnidium primitivum was the dominant tintinnid near the bottom waters. Our study clearly showed that aloricate ciliates and tintinnids had different vertical distributions and responses to freshwater discharge in the East China Sea.

De novo transcriptomes of a mixotrophic and a heterotrophic ciliate from marine plankton.

Studying non-model organisms is crucial in the context of the current development of genomics and transcriptomics for both physiological experimentation and environmental characterization. We investigated the transcriptomes of two marine planktonic ciliates, the mixotrophic oligotrich Strombidium rassoulzadegani and the heterotrophic choreotrich Strombidinopsis sp., and their respective algal food using Illumina RNAseq. Our aim was to characterize the transcriptomes of these contrasting ciliates and to identify genes potentially involved in mixotrophy. We detected approximately 10,000 and 7,600 amino acid sequences for S. rassoulzadegani and Strombidinopsis sp., respectively. About half of these transcripts had significant BLASTP hits (E-value <10−6) against previously-characterized sequences, mostly from the model ciliate Oxytricha trifallax. Transcriptomes from both the mixotroph and the heterotroph species provided similar annotations for GO terms and KEGG pathways. Most of the identified genes were related to housekeeping activity and pathways such as the metabolism of carbohydrates, lipids, amino acids, nucleotides, and vitamins. Although S. rassoulzadegani can keep and use chloroplasts from its prey, we did not find genes clearly linked to chloroplast maintenance and functioning in the transcriptome of this ciliate. While chloroplasts are known sources of reactive oxygen species (ROS), we found the same complement of antioxidant pathways in both ciliates, except for one enzyme possibly linked to ascorbic acid recycling found exclusively in the mixotroph. Contrary to our expectations, we did not find qualitative differences in genes potentially related to mixotrophy. However, these transcriptomes will help to establish a basis for the evaluation of differential gene expression in oligotrichs and choreotrichs and experimental investigation of the costs and benefits of mixotrophy.

Pyrosequencing for assessing diversity of eukaryotic microbes: analysis of data on marine planktonic ciliates and comparison with traditional methods

Assessing microbial diversity requires analysis of all three domains of life, including eukaryotic microbes. We examined the diversity of two ecologically important clades of microbial eukaryotes, ciliates in the subclasses Oligotrichia and Choreotrichia (class Spirotrichea), by comparing pyrosequencing to Sanger-sequenced clone libraries and microscopy. Using samples from a large temperate estuary (Long Island Sound, USA), we gained three major insights. First, richness estimates varied by up to one order of magnitude either using different criteria for pyrosequence processing or among pyrosequencing, cloning and microscopy, while taxon identification was almost always coherent. Error-correcting algorithms for pyrosequences ('denoising') reduced discrepancies in richness but also removed known morphospecies from the data. Second, although most of the pyrosequenced operational taxonomic units (OTUs) were distributed within known orders and families, we found evidence of a previously uncharacterized or unknown clade even in these ciliate lineages that have a rich history of morphological description. Third, pyrosequencing allowed the detection of OTUs that were either dominant or extremely rare in different samples. Our findings confirm the potential of pyrosequencing for quantifying microbial diversity, but also highlight the importance of careful evaluation of pyrosequence processing for using this method to address ecological questions.

海洋浮游纤毛虫生长率的研究进展

Marine planktonic ciliates are a link between microbial food web and classical food chain. They play a pivotal role in material cycling and energy flow in marine ecosystem. Since the 1970s,growth rates of marine planktonic ciliates have been studied in both laboratory and in situ. Only few laboratory studies on ciliate growth rates are available in China, and no field research has been carried out to determine the growth rates of planktonic ciliates. This review summarizes previous studies on the growth rates in both laboratory and in situ. Laboratory experiments show that the growth rates varied with food type and temperature. Under a certain temperature,ciliate would stop growing or die when food availability is below its threshold value. The growth rates could increase as food concentration increase over the threshold value,and then reach intrinsic growth rate( μmax),stay or drop slightly at a high food concentrations. Scientists estimated the μmaxvalues of 34 oligotrichous ciliate species in laboratory; and the values ranged 0. 1—3. 05 d-1. Feeding on a given prey,ciliate would stop growing or die at low temperature. μmaxincreased linearly with temperature in the intermediate range. Higher pH will restrain μmax. Size-fractionated seawater incubation was used to estimate in situ ciliate growth rate,from which the maximum growth rate was 3. 3 d-1. Temperature,hypoxia,and prey( bottom up control) influenced the ciliate growth rate in differentregions. Planktonic ciliate production,calculated according to ciliate abundance and growth rate,was higher than planktonic copepod production in most cases.

Redescription of Favella ehrenbergii (Claparède and Lachmann, 1858) Jörgensen, 1924 (Ciliophora: Choreotrichia), with Phylogenetic Analyses Based on Small Subunit rRNA Gene Sequences

The identification of Favella ehrenbergii, a marine planktonic ciliate, has largely been based on its lorica features. This approach is potentially problematic given the polymorphic lorica during this organism's life cycle. We isolated a population of F. ehrenbergii from the coastal waters of Incheon, Korea, and revealed its infraciliature using the protargol staining method. Phylogenetic analysis based on small subunit rRNA gene sequences was also performed. Results showed that this population possessed 16 collar membranelles (CM) and about 100 somatic kineties. These features are highly conserved, even in later dividers. As such, the number of CM and somatic kineties can be used as key characteristics for identification of Favella species.

Evaluation of the efficiency of metabolism of dinoflagellate phosphorus and carbon by a planktonic ciliate

The trophic transfer of nutrients through the microbial food web is a key top-down control in aquatic ecosystems which is notoriously difficult to evaluate, particularly for planktonic protists. In this study, a sensitive dual-radioactive tracer technique was developed to simultaneously assess the ingestion rate, and carbon- and phosphorus-specific assimilation efficiencies, of the marine planktonic ciliate Strobilidium neptuni feeding on the autotrophic dinoflagellate Heterocapsa triquetra. Dinoflagellate prey were simultaneously 16 h pulse labelled with NaH 14CO 3 and H 3 33PO 4 before being fed to the ciliate, and radioactive labels were traced into ciliate biomass and the experimental medium, as well as being monitored in the prey cells. Rates measured in short-term (10 min) incubations, as commonly used to estimate protist uptake of fluorescently labelled prey, were approximately 6 times higher and 3–6 times more variable than rates measured in longer 3–5 h incubations. The efficiency of accumulation of prey carbon (54±9%) by ciliates was lower than that of prey phosphorus (68±3%) suggesting that the phosphorus to carbon ratio in the ciliates was 1.3 times higher than in the labelled dinoflagellate biomass. Rates of phosphorus accumulation and release were combined to reveal that ciliates consumed 3.2±0.6 dinoflagellates cell −1 h −1. The assessment of carbon tracer release by ciliates was less reliable due to 14CO 2 exchange between the experimental media and air. The study concludes that the dual phosphorus–carbon radioactive tracer labelling of algal prey allowed the quantification of protist herbivory and nutrient remineralisation in laboratory experiments, thereby providing a potential technique for studying planktonic microbial trophic interactions in situ.

Redescriptions of two marine planktonic ciliates from China, Parastrombidium faurei (Kahl, 1932) Maeda, 1986 and Strombidium capitatum (Leegaard, 1915) Kahl, 1932 (Ciliophora, Oligotrichea)

The morphology and infraciliature of two marine planktonic ciliates, Parastrombidium faurei (Kahl, 1932) Maeda, 1986 and Strombidium capitatum (Leegaard, 1915) Kahl, 1932, from coastal waters near Qingdao (Tsingtao), northern China, were investigated based on live observation and protargol impregnation. This is the first time that these two species are reported from Yellow Sea/North Pacific. Emended diagnoses for the genus Parastrombidium and its single species P. faurei are provided as they were not studied with modern methods before. The ciliary pattern and the stomatogenesis of Parastrombidium indicate that it belongs to the order Choreotrichida Small and Lynn, 1985, family Strombidinopsidae Small and Lynn, 1985. An updated description for the “well-known” Strombidium capitatum is also included based on the Qingdao population.

Morphological studies on the infraciliature of a planktonic ciliate,Tintinnopsis brasiliensis (Ciliophora: Tintinina)

A poorly-described marine planktonic ciliate,Tintinnopsis brasiliensis Kofoid & Campbell, 1929, collected from the Taiping Cape of Qingdao, China, was morphologically investigated based on permanent preparation after protargol impregnation and was compared with other related congeners. According to the infraciliature, three ciliary groups can be recognized, which reveals a very stable structure among specimens and denotes that the pattern of infraciliature is, apart from the features of the lorica, a highly reliable criterion for species identification.

Is it the tortoise or the hare? Ciliates grazing on dinoflagellates in boom–bust dynamics

This mini‐review examines the maximum growth rate and threshold levels (the food level where growth rate is zero) of marine planktonic ciliates and heterotrophic dinoflagellates. There are strong indications that ciliates will out‐compete dinoflagellates, as they have higher maximum growth rates, lower threshold levels and are able to rapidly exploit both harmful and non‐harmful dinoflagellates as prey. I suggest that ciliates are neither the tortoise (slow and steady) nor the hare (fast and foolish), but the best combination of both. To some extent, this argument is raised as a “straw‐man” to be knocked down by discussion; the session is intended to serve as a platform for evaluating the relative importance of ciliates and heterotrophic dinoflagellates in marine ecosystems.