Insight into the role of cyanobacterial bloom in the trophic link between ciliates and predatory copepods

An important group of protozooplankton, the ciliates, are a crucial component of aquatic food webs. They are the main grazers on bacteria and algae transferring carbon to higher levels of the food web (metazooplankton and fish fry). Changes in the quality and quantity of protozooplankton can modify the quality and quantity of metazooplankton, especially predatory copepods, causing changes in energy transfer and the matter cycle. Observable climate change is one of the most significant factors promoting the increase of cyanobacterial blooms. Therefore, the aim of this study was to find out how cyanobacterial blooms modify relationships between ciliates (prey) and copepods (predator), and to discover possible pathways of changes in freshwater food webs. We analysed the relationship between the biomass of predatory copepods and feeding guilds of ciliates (algivorous, bacterivorous, bacteri-algivorous). The relationship of predators biomass with algivorous and bacteri-algivorous ciliate biomasses, with a simultaneous lack of relationship with bacterivorous ciliate biomass, demonstrates that bacterial fixed carbon may be only partially contributing to the total energy passed through this link. Results demonstrated that the bloom enhanced the relationship between prey and predator. Larger and free-swimming ciliate species appear to play a greater role in energy transfer than smaller sedentary species.

Trophic Enrichment Factors of Carbon and Nitrogen Isotopic Ratios (Δ13C and Δ15N) in Four Marine Ciliates

Understanding the magnitude and causes of isotopic fractionation between organisms and their dietary resources is crucial for gaining knowledge on stable isotope ecology. However, little is known regarding the diet-tissue fractionation values of marine ciliates, which play a critical role in the reconstruction of microbial food webs. In the present study, we conducted experiments on two benthic (Pseudokeronopsis pararubra and Protocruzia labiata) and two pelagic (Strombidium sulcatum and Uronemella filificum) marine ciliates, where they were fed with isotopically constant foods (Chaetoceros calcitrans and Isochrysis galbana) under laboratory culture conditions to determine their carbon and nitrogen isotopic fractionation values (Δ13C and Δ15N). The stable isotope values (δ13C and δ15N) of ciliates for all experiments rapidly increased after the initial feeding, with half-lives ranging from 6.1 to 23.0h for δ13C and from 3.1 to 24.9h for δ15N. The Δ13C and Δ15N for all ciliates represented significantly positive enrichments, with overall mean fractionations of 0.6±0.2 and 1.2±0.4, respectively. Irrespective of the dietary type, both Δ13C and Δ15N were very similar for the same ciliate species. These results suggest that Δ13C and Δ15N for marine ciliates are similar to those found in common marine organisms with very little food-dependent variation. Overall, quantifying the specific isotopic fractionation of marine ciliates is expected to provide fundamental information on the trophic transfer of carbon, nitrogen, and energy flow through the microbial pathway in marine ecosystems.

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.

Report of Acineta euchaetae Sewell, 1951 from new locality of the Arabian Sea with notes on their taxonomy and distribution

The article deals with the data about new find of the rare suctorian species Acineta euchaetae Sewell, 1951 on calanoid copepod host Euchaeta marina (Prestandrea, 1833) from the Arabian Sea. Seven young (sub-adult) individuals of the ciliate were observed on rear part of cephalothorax and on abdomen of adult male of copepod. The data about all known finds of A. euchaetae are discussed as well as the information on different developmental stages of the ciliate species. It is suggested that A. euchaetae is euryhaline species distributed in Eurasian coastal and inland waters and have preference for calanoid copepod hosts, but do not show specificity to any calanoid genus or species. The summarized diagnosis and refined systematic position of A. euchaetae are also provided.

A checklist of ciliates (Ciliophora) inhabiting on cnidarians

A compilation of the ciliate epibiont species (Ciliophora) found on marine and fresh water cnidarians has been carried out based on published records. The checklist includes the taxonomic position of each species of epibiontic ciliate, the species of basibiont cnidarians, the geographic zones and the bibliographic references where they were recorded. Cnidarians, especially colonial sessile forms, represent suitable substrates for numerous sessile and vagile ciliates. Altogether 79 ciliate species belong to five classes viz. Spirotrichea, Heterotrichea, Phyllopharingea, Suctorea and Oligohymenophorea were listed. The most diverce as epibions on cnidarians are representatives of Suctorea with 41 species and Peritrichia (under the class Oligohymenophorea) with 25 species. Three species belong to class Spirotrichea, four Heterotrichea and one Phyllopharingea. Among the other representatives (except Peritrichia) of class Oligohymenophorea, four species belong to subclass Scutucociliatia, one species each in subclass Hymenostomatia and Apostomatia. One suctorian species Ophryodendron abietinum and two species of peritrichs, Cothurnia cordylophora and Rhabdostyla sertularium one Heterotrichea Halofolliculina corallasia and one Scutucociliatia Philaster guamensis are likely specific to cnidarian hosts only.

Retention of Prey Genetic Material by the Kleptoplastidic Ciliate Strombidium cf. basimorphum

Many marine ciliate species retain functional chloroplasts from their photosynthetic prey. In some species, the functionality of the acquired plastids is connected to the simultaneous retention of prey nuclei. To date, this has never been documented in plastidic Strombidium species. The functionality of the sequestered chloroplasts in Strombidium species is thought to be independent from any nuclear control and only maintained via frequent replacement of chloroplasts from newly ingested prey. Chloroplasts sequestered from the cryptophyte prey Teleaulax amphioxeia have been shown to keep their functionality for several days in the ciliate Strombidium cf. basimorphum. To investigate the potential retention of prey genetic material in this ciliate, we applied a molecular marker specific for this cryptophyte prey. Here, we demonstrate that the genetic material from prey nuclei, nucleomorphs, and ribosomes is detectable inside the ciliate for at least 5 days after prey ingestion. Moreover, single-cell transcriptomics revealed the presence of transcripts of prey nuclear origin in the ciliate after 4 days of prey starvation. These new findings might lead to the reconsideration of the mechanisms regulating chloroplasts retention in Strombidium ciliates. The development and application of molecular tools appear promising to improve our understanding on chloroplasts retention in planktonic protists.

Phenotypic plasticity can reverse the relative extent of intra- and interspecific variability across a thermal gradient

Intra- and interspecific variability can both ensure ecosystem functions. Generalizing the effects of individual and species assemblages requires understanding how much within and between species trait variation is genetically based or results from phenotypic plasticity. Phenotypic plasticity can indeed lead to rapid and important changes of trait distributions, and in turn community functionality, depending on environmental conditions, which raises a crucial question: could phenotypic plasticity modify the relative importance of intra- and interspecific variability along environmental gradients? We quantified the fundamental niche of five genotypes in monocultures for each of five ciliate species along a wide thermal gradient in standardized conditions to assess the importance of phenotypic plasticity for the level of intraspecific variability compared to differences between species. We showed that phenotypic plasticity strongly influences trait variability and reverses the relative extent of intra- and interspecific variability along the thermal gradient. Our results show that phenotypic plasticity may lead to either increase or decrease of functional trait variability along environmental gradients, making intra- and interspecific variability highly dynamic components of ecological systems.

Molecular characterization and transcriptional regulation of two types of H+-pyrophosphatases in the scuticociliate parasite Philasterides dicentrarchi

Proton-translocating inorganic pyrophosphatases (H+-PPases) are an ancient family of membrane bound enzymes that couple pyrophosphate (PPi) hydrolysis to H+ translocation across membranes. In this study, we conducted a molecular characterization of two isoenzymes (PdVP1 and PdVP2) located in respectively the alveolar sacs and in the membranes of the intracellular vacuoles of a scuticociliate parasite (Philasterides dicentrarchi) of farmed turbot. We analyzed the genetic expression of the isoenzymes after administration of antiparasitic drugs and after infection in the host. PdVP1 and PdVP2 are encoded by two genes of 2485 and 3069 bp, which respectively contain 3 and 11 exons and express proteins of 746 and 810 aa of molecular mass 78.9 and 87.6 kDa. Topological predictions from isoenzyme sequences indicate the formation of thirteen transmembrane regions (TMRs) for PdVP1 and seventeen TMRs for PdVP2. Protein structure modelling indicated that both isoenzymes are homodimeric, with three Mg2+ binding sites and an additional K+ binding site in PdVP2. The levels of identity and similarity between the isoenzyme sequences are respectively 33.5 and 51.2%. The molecular weights of the native proteins are 158 kDa (PdVP1) and 178 kDa (PdVP2). The isoenzyme sequences are derived from paralogous genes that form a monophyletic grouping with other ciliate species. Genetic expression of the isoenzymes is closely related to the acidification of alveolar sacs (PdVP1) and intracellular vacuoles (PdVP2): antiparasitic drugs inhibit transcription, while infection increases transcription of both isoenzymes. The study findings show that P. dicentrarchi possesses two isoenzymes with H+-PPase activity which are located in acidophilic cell compartment membranes and which are activated during infection in the host and are sensitive to antiparasitic drugs. The findings open the way to using molecular modelling to design drugs for the treatment of scuticociliatosis.

The First Record of Intestinal Ciliates from the Mountain Zebra (Equus zebra) in South Africa

This paper is a first report on species of endosymbiotic ciliates (Litostomatea, Trichostomatia) inhabiting the intestine of zebras in South Africa. Ciliates from Mountain Zebra were investigated for the first time in the world. The wild population of mountain zebras in general and the Cape Mountain Zebra subspecies in particular is low in numbers: this species is included as vulnerable in the IUCN Red List. Approximately 15 species of trichostome ciliates from 9 different genera were found in the samples collected from wild zebras in Western Cape, South Africa. Some of the ciliate species are also common to horses and other equids, while others are unique for zebras. The ciliates of Triplumaria genus common to elephants and rhinoceroses, and the species Blepharosphaera ceratotherii previously described in rhinoceroses were found in equids for the first time.

The use of ciliated microeukaryotes and zooplankton in ecotoxicological studies: a look into the future

Aquatic ecosystems have been affected by different human activities (e.g., urbanization, industrial and agricultural activities) and hence, changing the water quality, the process, and function exercised by these environments. The evaluation of water quality through ecotoxicological studies has become an effective tool for understanding the effects of pollutants on biological communities, allowing the measurement of anthropogenic effects on aquatic systems. The use of microeukaryotes ciliates as bioindicators has been identified as a great potential for assessing water quality, however, these organisms are still neglected in ecotoxicological fields being necessary to enlarge the studies with these organisms. Moreover, the interaction effect among more than one environmental stressor (e.g., chemical contaminant, temperature) also needs to be more study due to the complexity of the aquatic ecosystems functioning. In the present study, we demonstrated through three chapters that the microeukaryotes ciliates can be included in the ecotoxicological studies since as long as they are expanded the classical ecotoxicological studies where it is possible to develop standard methods and deepen knowledge. Furthermore, a fourth chapter showed the interaction between more than one environmental stressor could contribute to a biodiversity decline and even, future research should be dedicated to assessing different interactions in the Mediterranean aquatic ecosystems. (Chapter 1) By means of a mini review, and discussed a brief history, the current scenario and pointing out their methodological approaches gaps of the ecotoxicological studies with ciliates. (Chapter 2) Performing a meta-analysis, we assessed the available toxicity data of heavy metals and ciliates. The results showed the tolerance of ciliates to heavy metals varies notably being partly influenced by differences in methodological conditions across studies. Moreover, most ciliates are tolerant to heavy metal pollution than the standard test species used in ecotoxicological risk assessments, i.e., Raphidocelis subcapitata, Daphnia magna, and Onchornyncus mykiss. Finally, this study highlighted the importance of developing standard toxicity test protocols for ciliates, which could lead to a better comprehension of the toxicological impact of heavy metals and other contaminants on ciliate species. (Chapter 3) By means of ecotoxicological tests, this study demonstrated the tolerance of Paramecium caudatum to caffeine. The results showed that this species had higher resistance in the environment. Even, we observed a moderate risk for P. caudatum regarding maximum environmental concentrations of caffeine in surface freshwater being that the global distribution of caffeine and the probability of increasing environmental concentrations highlight the need for more studies to better understand caffeine in aquatic ecosystems and the associated risks. (Chapter 4) Finally, by means of an indoor microcosm experiment, it was demonstrated that the temperature can influence the direct and indirect effects of salinity and pesticides on zooplankton communities in Mediterranean coastal wetlands and highlights vulnerable taxa and ecological responses that are expected to dominate under future global change scenarios.