Predation by Acartia tonsa Dana on planktonic ciliates and rotifers

In laboratory experiments, adults and nauplii of the calanoid copepod Acartia tonsa Dana feed on planktonic ciliates and rotifers. Adults have a higher clearing rate for planktonic ciliates and rotifers than for phytoplankton. Adult copepods have a maximum clearing rate of ≈200 ml copepod⁻¹ · d⁻¹ for large ciliates, with lower clearing rates for small ciliates. Nauplii have higher clearance for small than for large ciliates. Addition of ciliates or rotifers to the diet of A. tonsa enhances egg production; this effect is due to improved food quality. Microzooplankton may be an important component of the diet of A. tonsa even when phytoplankton are plentiful. Selective predation by copepods probably influences the population dynamics of planktonic ciliates and rotifers in coastal waters.     

Intracellular bacteria in ciliates

Ciliates are frequently colonized by other micro-organisms. The large size of ciliate cells offers habitats for hundreds to thousands of bacteria in different compartments, such as cytoplasm, nuclei and even perinuclear spaces. Size, phagocytic feeding habit and other features appear to be favorable pre-adaptations of ciliates for symbiosis with bacteria. Certain intracellular bacteria are permanent symbionts that are not infectious, whereas others are highly infectious. Both types show specific adaptations. With their wide spectrum of phylogenetic positions, intracellular bacteria in ciliates show relationships to different taxa of free-living bacteria and even archaea. Certain symbionts may be deleterious for their host ciliates, whereas others may provide a selective advantage under appropriate conditions or even be essential for the host cells. Depending on the nature of a symbiont, its prevalence in a host population may be low or high. Symbionts that express a killer toxin affecting non-infected ciliates achieve high infection rates in a host population. whereas certain infectious bacteria may only show a low prevalence.     

八种纤毛虫减数分裂基因的分子进化研究

减数分裂是真核生物适应性进化的重要机制,以8种纤毛虫作为实验对象,通过生物信息学方法对其14个减数分裂基因进行了鉴定及分子进化研究。结果表明:(1)不同的纤毛虫种类存在一些特异性的减数分裂基因的丢失与复制现象;(2)减数分裂相关基因在纤毛虫中很保守;(3)纤毛虫减数分裂重要的同源重组过程是在真核生物中不常见的Ⅱ型。本研究表明,纤毛虫减数分裂可能代表了真核生物较原始的减数分裂方式,在进化的过程中很保守,为研究真核生物减数分裂起源与进化提供了重要线索。     

Ciliates expel environmental legionella-laden pellets to stockpile food

When Tetrahymena ciliates are cultured with Legionella pneumophila, the ciliates expel bacteria packaged in free spherical pellets. Why the ciliates expel these pellets remains unclear. Hence, we determined the optimal conditions for pellet expulsion and assessed whether pellet expulsion contributes to the maintenance of growth and the survival of ciliates. When incubated with environmental L. pneumophila, the ciliates expelled the pellets maximally at 2 days after infection. Heat-killed bacteria failed to produce pellets from ciliates, and there was no obvious difference in pellet production among the ciliates or bacterial strains. Morphological studies assessing lipid accumulation showed that pellets contained tightly packed bacteria with rapid lipid accumulation and were composed of the layers of membranes; bacterial culturability in the pellets rapidly decreased, in contrast to what was seen in ciliate-free culture, although the bacteria maintained membrane integrity in the pellets. Furthermore, ciliates newly cultured with pellets were maintained and grew vigorously compared with those without pellets. In contrast, a human L. pneumophila isolate killed ciliates 7 days postinfection in a Dot/Icm-dependent manner, and pellets harboring this strain did not support ciliate growth. Also, pellets harboring the human isolate were resuscitated by coculturing with amoebae, depending on Dot/Icm expression. Thus, while ciliates expel pellet-packaged environmental L. pneumophila for stockpiling food, the pellets packaging the human isolate are harmful to ciliate survival, which may be of clinical significance.     

Spatial Distribution of Marine Ciliates: Micro-Ecologic and Biogeographic Aspects of Protozoan Ecology*†

SYNOPSIS Free-living marine ciliates occur in the interstitial spaces of a wide vareity of filamentous and particulate substrata, on the surfaces of planar substrata, and in the plankton. In addition, they are found in association with a wide variety of plant and animal hosts. In this paper I review the progress during the past decade in understanding the distribution of marine ciliates, with particular emphasis on the relationship between ciliate biogeography and the species problem. It is concluded that as a general rule among marine ciliates, genera and species complexes are cosmopolitan. Specific locales may support a confusing array of sibling species or subspecific morphologic variants. Because the distributional processes and breeding biology of marine ciliates are only beginning to be understood, conventional ideas that marine ciliate species are cosmopolitan may require modification.     

Acquired phototrophy in ciliates: a review of cellular interactions and structural adaptations

Many ciliates acquire the capacity for photosynthesis through stealing plastids or harboring intact endosymbiotic algae. Both phenomena are a form of mixotrophy and are widespread among ciliates. Mixotrophic ciliates may be abundant in freshwater and marine ecosystems, sometimes making substantial contributions toward community primary productivity. While mixotrophic ciliates utilize phagotrophy to capture algal cells, their endomembrane system has evolved to partially bypass typical heterotrophic digestion pathways, enabling metabolic interaction with foreign cells or organelles. Unique adaptations may also be found in certain algal endosymbionts, facilitating establishment of symbiosis and nutritional interactions, while reducing their fitness for survival as free-living cells. Plastid retaining oligotrich ciliates possess little selectivity from which algae they sequester plastids, resulting in unstable kleptoplastids that require frequent ingestion of algal cells to replace them. Mesodinium rubrum (=Myrionecta rubra) possesses cryptophyte organelles that resemble a reduced endosymbont, and is the only ciliate capable of functional phototrophy and plastid division. Certain strains of M. rubrum may have a stable association with their cryptophyte organelles, while others need to acquire a cryptophyte nucleus through feeding. This process of stealing a nucleus, termed karyoklepty, was first described in M. rubrum and may be an evolutionary precursor to a stable, reduced endosymbiont, and perhaps eventually a tertiary plastid. The newly described Mesodinium"chamaeleon," however, is less selective of which cryptophyte species it will retain organelles, and appears less capable of sustained phototrophy. Ciliates likely stem from a phototrophic ancestry, which may explain their propensity to practice acquired phototrophy.     

Ciliates in Extreme Environments

As eukaryotic microbial life, ciliated protozoan may be found actively growing in some extreme condition where there is a sufficient energy source to sustain it because they are exceedingly adaptable and not notably less adaptable than the prokaryotes. However, a crucial problem in the study of ciliates in extreme environments is the lack of reliable cultivation techniques. To our knowledge, only a tiny fraction of ciliates can be cultured in the laboratory, even for a very limited period, which can partly explain the paucity of our understanding about ciliates diversity in various extremes although the interest in the biodiversity of extremophiles increased significantly during the past three decades. This mini‐review aims to compile the knowledge of several groups of free‐living ciliates that can be microscopically observed in extreme environmental samples, although most habitats have not been sufficiently well explored for sound generalizations.     

Alpha/beta inversion of the Euplotes and Oxytricha tubulins.

Immunoblotting studies, using a polyclonal antibody specific for the alpha-tubulin of ciliates and an anti-beta-tubulin monoclonal antibody, demonstrated that the tubulins of the ciliates Euplotes and Oxytricha show alpha/beta inversion although less accentuated than that observed in Paramecium and Tetrahymena. Results suggest that (a) the alpha/beta inversion may be a common characteristic within the Phylum Ciliophora; and (b) the electrophoretic behaviour of the alpha-tubulin may be useful for establishing evolutionary relatedness between the ciliates.     

Effects of Metazoan Predators on Ciliates in Freshwater Plankton Communities1

ABSTRACT. Ciliates are often important members of aquatic communities in terms of their biomass, productivity, trophic roles, or numerical abundance. The interaction of metazoan predators with ciliates will be mediated by a number of biotic factors, including the potential of ciliate populations for growth, the relative size of ciliates and metazooplankton, the species structure of the metazooplankton, and the defenses of ciliates. This paper reviews some of the recent laboratory an field data pertaining to these particular factor. Studies have generally shown that metazoans can reduce ciliate population growth rates, but this impact varies greatly with the ciliate and metazoans involved. Smaller ciliates are generally more vulnerable to metazoan predators than larger species, although this relationship will be affected by the defenses a ciliate may possess. The structure of the metazooplankton community itself will also affect ciliatemetazoan interactions. The suppression of ciliate populations by metazoans has important ecological consequences, and more study is needed to understand the interaction of these groups in aquatic systems.     

Can the surface immobilization antigens of Philasterides dicentrarchi (Ciliophora: Scuticociliatida) be used as target antigens to develop vaccines in cultured fish?

In order to test whether immobilization antigens (i-antigens) of Philasterides dicentrarchi could be suitable antigenic targets against scuticociliatosis, polyclonal olive flounder (Paralichthys olivaceus) sera were raised against P. dicentrarchi by immunization with lysates of ciliates grown using chinook salmon epithelial (CHSE) cells, and the ability of the immune sera to kill the ciliates via classical complement pathway was analyzed in relation to agglutination activity. The immune sera showed clear agglutination activity against the CHSE-cultured ciliates. However, the agglutinated ciliates were not killed but escaped from the agglutinated mass within a few hours. Ciliates isolated from fish artificially infected with the same population of CHSE-cultured ciliates were not agglutinated by the immune sera even at the lowest dilution. In antibody-dependent complement-mediated killing (ADCK), the immune sera completely killed the CHSE-cultured ciliates at relatively higher serum dilutions (showing low or no agglutination activity). However, CHSE-cultured ciliates were not killed completely at lower immune serum dilutions (showing high agglutination activity). In contrast to CHSE-cultured ciliates, the ciliates isolated from infected fish were killed at lower dilutions of the immune sera in spite of no agglutination response. Considering the presence of various i-antigen types, ability to change i-antigen type in response to corresponding antibody, and relatively low ADCK activity at high agglutination titer, i-antigens of P. dicentrarchi may not be good targets for subunit vaccine development. To develop subunit vaccines against scuticociliatosis, other surface antigens expressed constitutively or expressed specifically under the infection state for survival of the ciliates in the host fish might be more favorable to elicit protective antibodies than the surface i-antigens.     

Biochemical composition of algivorous freshwater ciliates: you are not what you eat

The focus of our study was to determine whether the biochemical composition of two algivorous ciliates, both fed the same alga, resembles that of their diet. By comparing both ciliated protozoa we intended to identify species-specific differences in the metabolic features of these ciliates. Carbon- and cell-specific concentrations of fatty acids and essential amino acids were investigated for the ciliates Balanion planctonicum and Urotricha farcta grown on the cryptomonad Cryptomonas phaseolus. Stepwise discriminant analyses (SDA) indicated differences in the biochemical composition between ciliates and their diet and between the two ciliated protozoa. Carbon-specific fatty acid concentrations were usually higher in the ciliates than in their diet, especially concentrations of monounsaturated and some polyunsaturated fatty acids. Except for tryptophan, valine, and lysine, amino acid concentrations were higher in the ciliates than in C. phaseolus. Furthermore, differences in the polyunsaturated fatty acids accounted for the largest discrepancies between the two ciliated protozoa. The higher concentrations in the ciliates compared to their diet suggest that these species are capable of efficiently ingesting, assimilating or possibly synthesizing some fatty acids and amino acids. We conclude that dietary fatty acid and amino acid composition influences the composition of the two ciliated protozoa to a minor extent, and that species-specific differences in fatty acid and amino acid metabolism may be more important determinants of the biochemical composition of the studied ciliates. Moreover, the metabolism of polyunsaturated fatty acids seems to differ more profoundly between the two ciliated protozoa than the metabolism of other fatty acid classes or amino acids.     

Foreign Organelle Retention by Ciliates

SYNOPSIS. Intact algal chloroplasts were found by electron microscopy in the peripheral cytoplasm of 2 ecologically important species of planktonic marine ciliates. The exact origin of the chloroplast is uncertain and the periods of their retention by the protozoa is unknown. The 2 ciliate species may function partially or fully as primary producers. In other ciliates algal eye-spots are retained and may actually be utilized. Ecologic and evolutionary implications of the observations are discussed.     

Leptomonas ciliatorum n. sp. (Kinetoplastida,Trypanosomatidae) in the Macronucleus of a Hypotrichous Ciliate1

A leptomonad flagellate found in the macronucleus of the hypotrichous ciliate Paraholosticha sterkii carries out its whole life cycle there. The ciliates can divide, encyst, and excyst even when parasitized, and the flagellates are maintained throughout. Parasite-free ciliates may be rapidly infected. The light- and electron-microscopic structure of the flagellate resembles that of other leptomonads.     

Molecular Evidence that Phylogenetically Diverged Ciliates Are Active in Microbial Mats of Deep-Sea Cold-Seep Sediment

ABSTRACT. Cold seeps are areas of the seafloor where hydrogen sulfide- and methane-rich fluid seepage occurs, often sustaining chemosynthetic ecosystems. It is well known that both archaea and bacteria oxidize sulfides and methane to produce chemical energy and that several endemic animals use this energy to thrive in cold seeps. On the other hand, there is little knowledge regarding diversity and ecology of microbial eukaryotes in this ecosystem. In this study we isolated environmental RNA and DNA from microbial mats of cold-seep sediment in Sagami Bay, Japan, and retrieved eukaryotic small-subunit ribosomal RNA sequences with polymerase chain reaction methods followed by clone library construction. Most RNA-derived clones obtained were from ciliates, although DNA-derived clones were mainly from the fungus Cryptococcus curvatus , suggesting that ciliates are active in the environment. The ciliate sequences were phylogenetically diverse, and represented eight known class lineages as well as undesignated lineages. Because most ciliates are bacterivorous, it is highly likely that the ciliates for which sequences were recovered play a role in the food web of this ecosystem as grazers of microbial mats. In addition, given that the environment studied is under highly reduced (anoxic) conditions, based on the prokaryotic community structure deduced from T-RFLP profiles, the ciliates detected may be obligatory or facultative anaerobes.     

Population Dynamics of Active and Total Ciliate Populations in Arable Soil Amended with Wheat

Soil protozoa are characterized by their ability to produce cysts, which allows them to survive unfavorable conditions (e.g., desiccation) for extended periods. Under favorable conditions, they may rapidly excyst and begin feeding, but even under optimal conditions, a large proportion of the population may be encysted. The factors governing the dynamics of active and encysted cells in the soil are not well understood. Our objective was to determine the dynamics of active and encysted populations of ciliates during the decomposition of freshly added organic material. We monitored, in soil microcosms, the active and total populations of ciliates, their potential prey (bacteria and small protozoa), their potential competitors (amoebae, flagellates, and nematodes), and their potential predators (nematodes). We sampled with short time intervals (2 to 6 days) and generated a data set, suitable for mathematical modeling. Following the addition of fresh organic material, bacterial numbers increased more than 1,400-fold. There was a temporary increase in the number of active ciliates, followed by a rapid decline, although the size of the bacterial prey populations remained high. During this initial burst of ciliate growth, the population of cystic ciliates increased 100-fold. We suggest that internal population regulation is the major factor governing ciliate encystment and that the rate of encystment depends on ciliate density. This model provides a quantitative explanation of ciliatostasis and can explain why protozoan growth in soil is less than that in aquatic systems. Internally governed encystment may be an essential adaptation to an unpredictable environment in which individual protozoa cannot predict when the soil will dry out and will survive desiccation only if they have encysted in time.     

Anti‐helminth‐induced changes in the prevalence of entodiniomorphid ciliates in semi‐captive chimpanzees

Ciliates are some of the most abundant gut fauna in wild chimpanzees. However, their presence in captive populations is usually low presumably due to anti‐helmintic prophylaxis or feeding on low fibre diet. We studied a semi‐captive colony of chimpanzees at the Sweetwaters Sanctuary in Kenya subject to routine prophylactic dose of albendazole to clear chimpanzees of parasitic helminths. Fresh faecal samples from known individuals were collected before and subsequently after prophylaxis. The samples were fixed in 10% formalin and examined by the sedimentation method. Troglodytella abrassarti had 42.5% prevalence whereas other ciliates had 65% prevalence. The prevalence of the T. abrassarti and other ciliates significantly declined immediately after prophylaxis and then rose slowly thereafter. Our results suggest that ciliates are susceptible to anti‐helmintic prophylaxis and that treatment may eliminate ciliates or inhibit their proliferation within the host subsequently lowering their prevalence in the population. Variation in prevalence was not influenced by the age of the host. However, a steady recovery of ciliate prevalence was lower for male compared to female hosts. Our results imply that the intervals between prophylactic regimes could be prolonged differently for males and females to increase the prevalence of ciliates in captive populations.     

Anaerobiosis and Symbiosis with Bacteria in Free-living Ciliates

SYNOPSIS. Marine, sediment-dwelling ciliates were examined for cytochrome oxidase activity by a cytochemical method and for fine structural details. Species of Plagiopylidae (Trichostomatida), i.e. Plagiopyla frontata, Sonderia vorax and Sonderia sp., and of Heterotrichida, i.e., Parablepharisma pellitum, Parablepharisma sp., Metopus contortus, Metopus vestitus and Caenomorpha capucina ; previously considered to be obligate anaerobes because of their sulfide-containing habitat, do not have cytochrome oxidase activity or mitochondria with cristae or tubuli. The evolutionary origin and significance of anaerobic ciliates is discussed. Most of the anaerobic ciliates harbor a flora of ecto- and endosymbiotic bacteria as demonstrated by transmission and scanning electron micrographs. It is speculated that the bacteria may utilize the metabolic end products of the protozoa for growth and energy yielding processes. These associations are also compared with other, previously described cases of symbiosis involving prokaryotes and protozoa.     

Population dynamics of active and total ciliate populations in arable soil amended with wheat

Soil protozoa are characterized by their ability to produce cysts, which allows them to survive unfavorable conditions (e.g., desiccation) for extended periods. Under favorable conditions, they may rapidly excyst and begin feeding, but even under optimal conditions, a large proportion of the population may be encysted. The factors governing the dynamics of active and encysted cells in the soil are not well understood. Our objective was to determine the dynamics of active and encysted populations of ciliates during the decomposition of freshly added organic material. We monitored, in soil microcosms, the active and total populations of ciliates, their potential prey (bacteria and small protozoa), their potential competitors (amoebae, flagellates, and nematodes), and their potential predators (nematodes). We sampled with short time intervals (2 to 6 days) and generated a data set, suitable for mathematical modeling. Following the addition of fresh organic material, bacterial numbers increased more than 1,400-fold. There was a temporary increase in the number of active ciliates, followed by a rapid decline, although the size of the bacterial prey populations remained high. During this initial burst of ciliate growth, the population of cystic ciliates increased 100-fold. We suggest that internal population regulation is the major factor governing ciliate encystment and that the rate of encystment depends on ciliate density. This model provides a quantitative explanation of ciliatostasis and can explain why protozoan growth in soil is less than that in aquatic systems. Internally governed encystment may be an essential adaptation to an unpredictable environment in which individual protozoa cannot predict when the soil will dry out and will survive desiccation only if they have encysted in time.     

Anaerobiosis and symbiosis with bacteria in free-living ciliates.

Marine, sediment-dwelling ciliates were examined for cytochrome oxidase activity by a cytochemical method and for fine structural details. Species of Plagiopylidae (Trichostomatida), i.e. Plagiopyla frontata, Sonderia vorax and Sonderia sp., and of Heterotrichda, i.e., Parablepharisma pellitum, Parablepharisma sp., Metopus contortus, Metopus vestitus and Caenomorpha capucina; previously considered to be obligate anaerobes because of their sulfide-containing habitat, do not have cytochrome oxidase activity or mitochondria with cristae or tubuli. The evolutionary origin and significance of anaerobic ciliates is discussed. Most of the anaerobic ciliates harbor a flora of ecto- and endosymbiotic bacteria as demonstrated by transmission and scanning electron micrographs. It is speculated that the bacteria may utilize the metabolic end products of the protozoa for growth and energy yielding processes. These associations are also compared with other, previously described cases of symbiosis involving prokaryotes and protozoa.     

Evaluation of double formalin--Lugol's fixation in assessing number and biomass of ciliates: an example of estimations at mesoscale in NE Atlantic

Ciliated protozoa are potential grazers of primary and bacterial production and act as intermediaries between picoplankton and copepods and other large suspension feeders. Accurate determination of ciliate abundance and feeding mode is crucial in oceanic carbon budget estimations. However, the impact of different fixatives on the abundance and cell volume of ciliates has been investigated in only a few studies using either laboratory cultures or natural populations. Lugol's solution and formalin are the most commonly used fixatives for the preservation of ciliates samples. In the present study, the aim was to compare 0.4% Lugol's solution and 2% borated-formalin fixation and evaluate the need of counting duplicate samples each using a different fixative. For this, a large number of samples (n = 110) from the NE Atlantic was analyzed in the frame of POMME program (Multidisciplinary Mesoscale Ocean Program). We established a statistically significant relationship (p < 0.0001) between Lugol's and formalin fixed samples for both abundance (r2 = 0.50) and biomass (r2 = 0.76) of aloricate ciliates which showed that counts were higher in Lugol's solution by a factor of 2 and a non-taxon specific cell-loss in formalin. However, loricate ciliate abundance in our samples which were represented primarily by Tintinnus spp. did not show any difference between the two treatments. Abundance and biomass of mixotrophic ciliates (chloroplast-bearing cells) were for various reasons underestimated in both treatments. Our results show that unique fixation by formalin may severely underestimate ciliates abundance and biomass although their population may not alter. For this reason, Lugol's solution is best for the estimation of their abundance and biomass. However, for counts of mixotrophs and the evaluation of the ecological role of ciliates in carbon flux, double fixation is essential. Compromises regarding the fixatives have lead to severe underestimations of mixotrophs in studies conducted by now.