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Microplastic particles are ubiquitous in aquatic environments and are considered a major threat to the large range of heterotrophic organisms that involuntarily consume them. However, there is current uncertainty around the mechanisms underpinning microplastic uptake by aquatic consumers and the consequences for both the fate of the microplastics and the growth potential of consumer populations. We performed a feeding experiment, exposing a model freshwater ciliate, Tetrahymena pyriformis, to six different microplastic concentrations and measured microplastic uptake and population growth over the course of several generations. Microplastic uptake increased in a saturating fashion with concentration, consistent with a Type II functional response, with a maximum feeding rate of 22 microplastic particles individual -1  h -1 . Interestingly, microplastic uptake decreased through time and we observed that, after egestion, microplastic particles aggregated, rendering them too large for re-consumption. We built and tested a simulation model which matched rates of microplastic uptake when incorporating functional response parameters and assuming 50 % immobilisation of microplastics after egestion. Nevertheless, ciliate population growth was compromised by the presence of microplastics, decreasing by 43 % over the full microplastic concentration range. Taken together, our results demonstrate the potential for aquatic ciliates to play an important role in the uptake, transfer, and modification of microplastics in freshwater environments with associated negative impacts on population fitness., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 The Authors. Published by Elsevier B.V. All rights reserved.)

Human adenoviruses are ubiquitous contaminants of surface water. Indigenous protists may interact with adenoviruses and contribute to their removal from the water column, though the associated kinetics and mechanisms differ between protist species. In this work, we investigated the interaction of human adenovirus type 2 (HAdV2) with the ciliate Tetrahymena pyriformis . In co-incubation experiments in a freshwater matrix, T. pyriformis was found to efficiently remove HAdV2 from the aqueous phase, with ≥4 log 10 removal over 72 hours. Neither sorption onto the ciliate nor secreted compounds contributed to the observed loss of infectious HAdV2. Instead, internalization was shown to be the dominant removal mechanism, resulting in the presence of viral particles inside food vacuoles of T. pyriformis , as visualized by transmission electron microscopy. The fate of HAdV2 once ingested was scrutinized and no evidence of virus digestion was found over the course of 48 hours. This work shows that T. pyriformis can exert a dual role in microbial water quality: while they remove infectious adenovirus from the water column, they can also accumulate infectious viruses.

A quantitative structure-toxicity relationship (QSTR) model based on four descriptors was successfully developed for 1163 chemical toxicants against Tetrahymena pyriformis by applying general regression neural network (GRNN). The training set consisting of 600 organic compounds was used to train GRNN models that were evaluated with the test set of 563 compounds. For the optimal GRNN model, the training set possesses the coefficient of determination R 2 of 0.86 and root mean square (rms) error of 0.41, and the test set has R 2 of 0.80 and rms of 0.41. Investigated results indicate that the optimal GRNN model is accurate, although the GRNN model has only four descriptor and more samples in the test set., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The unicellular Tetrahymena distinguishes structure-related vertebrate hormones by its chemosensory reactions. In the present work, the selectivity of hormone receptors was evaluated by analyzing the effects of various gonadotropin-releasing hormone (GnRH) analogs (GnRH-I, GnRH-III) as well as truncated (Ac-SHDWKPG-NH 2 ) and dimer derivatives ([GnRH-III(C)] 2 and [GnRH-III(CGFLG)] 2 ) of GnRH-III on (i) locomotory behaviors, (ii) cell proliferation, and (iii) intracellular hormone contents of Tetrahymena pyriformis . The migration, intracellular hormone content, and proliferation of Tetrahymena were investigated by microscope-assisted tracking analysis, flow cytometry, and a CASY TT cell counter, respectively. Depending on the length of linker sequence between the two GnRH-III monomers, the GnRH-III dimers had the opposite effect on Tetrahymena migration. [GnRH-III(CGFLG)] 2 dimer had a slow, serpentine-like movement, while [GnRH-III(C)] 2 dimer had a rather linear swimming pattern. All GnRH-III derivatives significantly induced cell growth after 6 h incubation. Endogenous histamine content was uniformly enhanced by Ac-SHDWKPG-NH 2 and GnRH-III dimers, while some differences between the hormonal activities of GnRHs were manifested in their effects on intracellular levels of serotonin and endorphin. The GnRH peptides could directly affect Tetrahymena migration and proliferation in a structure-dependent manner, and they could indirectly regulate these reactions by paracrine/autocrine mechanisms. Present results support the theory that recognition ability and selectivity of mammalian hormone receptors can be deduced from a phylogenetically ancient level like the unicellular Tetrahymena .

The continuous and extensive use of pesticides, particularly in the field of agriculture, leads to contamination of all ecosystems (water, soil, and atmosphere). Among pesticides, fungicides constitute a larger group whose impact on the environment are still poorly studied. Difenoconazole belongs to triazole group of fungicides having high photochemical stability and have low biodegradability, which makes them persistent in water bodies. The present study focuses on the physiological and cytotoxic impact of difenoconazole fungicide on ciliated protozoa, Tetrahymena pyriformis with reference to growth, morphology, behaviour and its generation time. Morphological studies showed changes in the shape and size of T. pyriformis. Our result showed an inhibitory effect on population growth of T. pyriformis and the IC 50 concentration was found to be 6.8 μg mL -1 .The numbers of generations decreased and generation time was found to be extended in a concentration and time dependent manner. Difenoconazole caused significant depletion in phagocytic activity and also ultra-structural changes were observed by Transmission electron microscopy (TEM) analysis. The results indicate that the Tetrahymena toxicity assay could be used as a complementary system to rapidly elucidate the cytotoxic potential of fungicide., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Skin sensitization is an important occupational health problem and immunotoxicity endpoint. Considering animal welfare and time and cost savings, many alternative approaches, such as those conducted in vitro, in silico, and in chemo, have been proposed and applied to predict skin sensitization of compounds. Toxicologically, sensitizers can elicit excess toxicity at greater levels than non-sensitizers due to their capacity to react with proteins/peptides. Based on this understanding, calculated toxicity enhancements (T e ) of 65 organic compounds from three in vitro bioassays, i.e. 48-hr ciliate (Tetrahymena pyriformis) growth inhibition, and both 96-hr fathead minnow and 48-hr Daphnia magna acute lethal toxicities, were employed to qualitatively and quantitatively predict skin sensitization potencies of the test agents. The sensitivity, specificity, and accuracy reaching 80% strongly suggested toxicity enhancement was an excellent parameter for predicting skin sensitization. Linear regressions of skin sensitization against toxicity enhancement were fitted for each bioassay, and they were improved after the sensitizers were categorized into different reaction mechanistic domains, which, in decreasing order of contribution from T e to sensitization, were S N Ar > S N 1 > MA. These results indicated that toxicity bioassays are useful tools and that T e could be a useful parameter that might be applied to predict skin sensitization.

Endosymbiotic interactions are frequently found in nature, especially in the group of protists. Even though many endosymbioses have been studied in detail, little is known about the mechanistic origins and physiological prerequisites of endosymbiont establishment. A logical step towards the development of endocytobiotic associations is evading digestion and escaping from the host's food vacuoles. Surface properties of bacteria are probably involved in these processes. Therefore, we chemically modified the surface of a transformant strain of Escherichia coli prior to feeding to Tetrahymena pyriformis. N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide allows any substance carrying amino- or carboxyl groups to be bound covalently to the bacterial surface by forming a peptide bond, thus, altering its properties biochemically and biophysically in a predictable manner. The effect of different traits on digestion of T. pyriformis was examined by fluorescence and transmission electron microscopy. The efficiency of digestion differs considerably depending on the coupled substances. Alkaline substances inhibit digestion partially, resulting in incomplete digestion and slightly enhanced escape rates. Increasing hydrophobicity leads to much higher escape frequencies. Both results point to possible mechanisms employed by pathogenic bacteria or potential endosymbionts in evading digestion and transmission to the host's cytoplasm., (© 2018 The Author(s) Journal of Eukaryotic Microbiology © 2018 International Society of Protistologists.)

An important habit of ciliates, namely, their behavioral preference for walls, is revealed through experiments and hydrodynamic simulations. A simple mechanical response of individual ciliary beating (i.e., the beating is stalled by the cilium contacting a wall) can solely determine the sliding motion of the ciliate along the wall and result in a wall-preferring behavior. Considering ciliate ethology, this mechanosensing system is likely an advantage in the single cell's ability to locate nutrition. In other words, ciliates can skillfully use both the sliding motion to feed on a surface and the traveling motion in bulk water to locate new surfaces according to the single "swimming" mission., Competing Interests: The authors declare no conflict of interest., (Copyright © 2018 the Author(s). Published by PNAS.)

Mycobacteria are widespread microorganisms that live in various environments, including man-made water systems where they cohabit with protozoa. Environmental mycobacterial species give rise to many opportunistic human infections and can infect phagocytic protozoa. Protozoa such as amoebae and ciliates feeding on bacteria can sometimes get rid of non-digestible or pathogenic material by packaging it into secreted fecal pellets. Usually, packaged bacteria are still viable and are protected against chemical and physical stresses. We report here that mycobacteria can be packaged into pellets by ciliates. The model bacterium Mycobacterium smegmatis survived digestion in food vacuoles of the ciliate Tetrahymena pyriformis and was included in expelled fecal pellets. LIVE/DEAD® staining confirmed that packaged M. smegmatis cells preserved their viability through the process. Scanning and transmission electron microscopy revealed that bacteria are packaged in undefined filamentous and/or laminar substances and that just a thin layer of material seemed to keep the pellet contents in a spherical shape. These results imply that packaging of bacteria is more common than expected, and merits further study to understand its role in persistence and dissemination of pathogens in the environment., (© FEMS 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The soil is a complex ecosystem where interactions between biotic and abiotic factors determine the survival and fate of microbial inhabitants of the system. Having previously shown that Escherichia coli requires the general stress response regulator, RpoS, to survive long term in soil, it was important to determine what specific conditions in this environment necessitate a functional RpoS. This study investigated the susceptibility of soil-persistent E. coli to predation by the single-celled eukaryotes Acanthamoeba polyphaga and Tetrahymena pyriformis, and the role RpoS plays in resisting this predation. Strain-specific differences were observed in the predation of E. coli strains, with soil-persistent strain COB583 being the most resistant to predation by both protozoans. RpoS and curli, proteinaceous fibres used for attachment to biotic and abiotic surfaces, increased the ability of E. coli to resist predation by A. polyphaga and T. pyriformis. Furthermore, soil moisture content impacted the survival of E. coli BW25113 but wild-type COB583 had similar survival irrespective of soil moisture content. Overall, this study confirmed that RpoS contributes to the resistance of E. coli to protozoan predation and that RpoS is crucial for the increased fitness of soil-persistent E. coli against predation and reduced moisture in soil., (© FEMS 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Despite considerable research on the environmental impacts of nanomaterials, we know little about how they influence interactions between species. Here, we investigated the acute (12 d) and chronic (64 d) toxicities of cerium oxide nanoparticles (CeO 2 NPs) and bulk particles (0-200 mg/L) to three ciliated protist species (Loxocephalus sp., Paramecium aurelia, and Tetrahymena pyriformis) in single-, bi-, and multispecies microcosms. The results show that CeO 2 NPs strongly affected the interactions between ciliated protozoan species. When exposed to the highest CeO 2 NPs (200 mg/L), the intrinsic growth rates of Loxocephalus and Paramecium were significantly decreased by 18.87% and 88.27%, respectively, while their carrying capacities declined by more than 90%. However, CeO 2 NP exposure made it difficult to predict outcomes of interspecific competition between species. At higher NP exposure (100 and 200 mg/L), competition led to the extinction of both species in the Loxocephalus and Paramecium microcosms that survived in the absence of competitors or CeO 2 NPs. Further, the presence of potential competitors improved the survival of Loxocephalus to hundreds of individuals per milliliter in microcosms with Tetrahymena where Loxocephalus would otherwise not be able to tolerate high levels of NP exposure. This result could be attributed to weakened NP adsorption on the cell surface due to competitor-caused reduction of NP surface charge (from -18.52 to -25.17 mV) and intensified NP aggregation via phagocytosis of NPs by ciliate cells. Our results emphasize the need to explicitly consider species interactions for a more comprehensive understanding of the ecological consequences of NP exposure.

Background: Species recovery after disturbances depends on the strength and duration of disturbance, on the species traits and on the biotic interactions with other species. In order to understand these complex relationships, it is essential to understand mechanistically the transient dynamics of interacting species during and after disturbances. We combined microcosm experiments with simulation modelling and studied the transient recovery dynamics of a simple microbial food web under pulse and press disturbances and under different predator couplings to an alternative resource., Results: Our results reveal that although the disturbances affected predator and prey populations by the same mortality, predator populations suffered for a longer time. The resulting diminished predation stress caused a temporary phase of high prey population sizes (i.e. prey release) during and even after disturbances. Increasing duration and strength of disturbances significantly slowed down the recovery time of the predator prolonging the phase of prey release. However, the additional coupling of the predator to an alternative resource allowed the predator to recover faster after the disturbances thus shortening the phase of prey release., Conclusions: Our findings are not limited to the studied system and can be used to understand the dynamic response and recovery potential of many natural predator-prey or host-pathogen systems. They can be applied, for instance, in epidemiological and conservational contexts to regulate prey release or to avoid extinction risk of the top trophic levels under different types of disturbances.

Toxicity of human blood serum for ciliate Tetrahymena pyriformis is determined by the complement system. When ciliate are dying after being exposed to blood serum, cell membrane permeability for low-molecular-weight compounds significantly increases, probably due to pore formation. Serine protease inhibitors or exposure to physical factors inducing complement inactivation (e.g., heating up to 56°C) completely prevented ciliate death under the effect of human serum. Activation of serum complement upon interaction with Tetrahymena cells occurred by the classical or lectin pathway, while the contribution of the alternative activation pathway was negligible.

Escherichia coli O157:H7 is a food-borne bacterium that causes hemorrhagic diarrhea and hemolytic uremic syndrome in humans. While cattle are a known source of E. coli O157:H7 exposure resulting in human infection, environmental reservoirs may also be important sources of infection for both cattle and humans. Bacteriophage-encoded Shiga toxins (Stx) carried by E. coli O157:H7 may provide a selective advantage for survival of these bacteria in the environment, possibly through their toxic effects on grazing protozoa. To determine Stx effects on protozoan grazing, we co-cultured Paramecium caudatum, a common ciliate protozoon in cattle water sources, with multiple strains of Shiga-toxigenic E. coli O157:H7 and non-Shiga toxigenic cattle commensal E. coli. Over three days at ambient laboratory temperature, P. caudatum consistently reduced both E. coli O157:H7 and non-Shiga toxigenic E. coli populations by 1-3 log cfu. Furthermore, a wild-type strain of Shiga-toxigenic E. coli O157:H7 (EDL933) and isogenic mutants lacking the A subunit of Stx 2a, the entire Stx 2a-encoding bacteriophage, and/or the entire Stx 1-encoding bacteriophage were grazed with similar efficacy by both P. caudatum and Tetrahymena pyriformis (another ciliate protozoon). Therefore, our data provided no evidence of a protective effect of either Stx or the products of other bacteriophage genes on protozoan predation of E. coli. Further research is necessary to determine if the grazing activity of naturally-occurring protozoa in cattle water troughs can serve to decrease cattle exposure to E. coli O157:H7 and other Shiga-toxigenic E. coli.

Adrenomedullin (AMD), proadrenomedullin N-terminal 20 peptide (PAMP) and calcitonin gene-related peptide (CGRP) were studied for chemotaxis, chemotactic selection and G-actin/F-actin transition in Tetrahymena. The aim of the experiments was to study the effects of two different peptides encoded by the same gene compared to a peptide related to one of the two, but encoded by a different gene, at a low level of phylogeny. The positive, chemotactic effect of ADM and the strong negative, chemorepellent effect of PAMP suggest that in Tetrahymena, the two peptides elicit their chemotactic effects via different signalling mechanisms. The complexity of swimming behaviour modulated by the three peptides underlines that chemotaxis, chemokinesis and some characteristics of migratory behaviour (velocity, tortuosity) are working as a sub-population level complex functional unit. Chemotactic responsiveness to ADM and CGRP is short-term, in contrast to PAMP, which as a chemorepellent ligand, has the ability to select sub-populations with negative chemotactic responsiveness. The different effects of ADM and PAMP on the polymerization of actin networks show that the microtubular structure of cilia is more essential to chemotactic response than are transitions of the actin network. The results draw attention to the characteristic effects of vasoactive peptides at this low level of phylogeny.

Antibiotics leak constantly into environments due to widespread use in agriculture and human therapy. Although sublethal concentrations are well known to select for antibiotic-resistant bacteria, little is known about how bacterial evolution cascades through food webs, having indirect effect on species not directly affected by antibiotics (e.g. via population dynamics or pleiotropic effects). Here, we used an experimental evolution approach to test how temporal patterns of antibiotic stress, as well as migration within metapopulations, affect the evolution and ecology of microcosms containing one prey bacterium, one phage and two protist predators. We found that environmental variability, autocorrelation and migration had only subtle effects for population and evolutionary dynamics. However, unexpectedly, bacteria evolved greatest fitness increases to both antibiotics and enemies when the sublethal levels of antibiotics were highest, indicating positive pleiotropy. Crucially, bacterial adaptation cascaded through the food web leading to reduced predator-to-prey abundance ratio, lowered predator community diversity and increased instability of populations. Our results show that the presence of natural enemies can modify and even reverse the effects of antibiotics on bacteria, and that antibiotic selection can change the ecological properties of multitrophic microbial communities by having indirect effects on species not directly affected by antibiotics., (© 2015 The Author(s) Published by the Royal Society. All rights reserved.)

Chemotaxis is one of the most essential cell physiological responses, which was developed in parallel the molecular evolution of signal molecules. Previously good correlations were found between chemotactic moieties and physicochemical properties (SEA, solubility, pKa) of peptide type ligands in Tetrahymena model. However, references are rather weak in eukaryotic chemotaxis about significance of simple carbohydrates. In the present work our goal is (i) to investigate the chemotactic effect of 10 mono- and disaccharides in the eukaryotic Tetrahymena pyriformis; (ii) to describe effective ligands with physicochemical parameters; (iii) to test whether sugars are acting via induction of metabolic pathways. Our results are: (i) the tested sugars can trigger both significant attractant (D-glucose, D-mannose) and significant repellent (D-glucosamine, D-fructose, N-acetyl-D-galactosamine, D-arabinose) effects, while some of the sugars (maltose, lactose, sucrose, D-galactose) had no effect. (ii) Correlations were described between the chemotactic effectiveness of the ligands and their physicochemical characters (TPSA, XLogP), which are supposed to influence the internalization of the sugars. (iii) All ligands proved to have low selection potential, which refers to a 'short-term' receptor moiety or influencing specific metabolic pathways. (iv) Starvation elicited modified, strong chemoattractive responsiveness towards glucose; however, it was independent of concentration while 1 h insulin treatment resulted in an increased and concentration dependent chemotaxis induced by glucose., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Survival of enteric bacteria in aquatic habitats varies depending upon species, strain, and environmental pressures, but the mechanisms governing their fate are poorly understood. Although predation by protozoa is a known, top-down control mechanism on bacterial populations, its influence on the survival of fecal-derived pathogens has not been systematically studied. We hypothesized that motility, a variable trait among pathogens, can influence predation rates and bacterial survival. We compared the survival of two motile pathogens of fecal origin by culturing Escherichia coli O157 and Salmonella enterica Typhimurium. Each species had a motile and non-motile counterpart and was cultured in outdoor microcosms with protozoan predators (Tetrahymena pyriformis) present or absent. Motility had a significant, positive effect on S. enterica levels in water and sediment in the presence or absence of predators. In contrast, motility had a significant negative effect on E. coli O157 levels in sediment, but did not affect water column levels. The presence/absence of protozoa consistently accounted for a greater proportion of the variability in bacterial levels (>95 %) than in bacterial motility (<4 %) in the water column. In sediments, however, motility was more important than predation for both bacteria. Calculations of total CFU/microcosm showed decreasing bacterial concentrations over time under all conditions except for S. enterica in the absence of predation, which increased ∼0.5-1.0 log over 5 days. These findings underscore the complexity of predicting the survival of enteric microorganisms in aquatic habitats, which has implications for the accuracy of risk assessment and modeling of water quality.

In eukaryotic cells that multiply by binary fission, the interaction of actin filaments with myosin II in the contractile ring is widely recognized to generate force for membrane ingression into the cleavage furrow; however, the expression of myosin II is restricted in animals, yeast, fungi, and amoeba (collectively, unikonts). No corresponding motor protein capable of forming mini-filaments that could exert sufficient tension to cleave the cell body is found in bikonts, consisting of planta, algae, and most protozoa; however, cells in some bikont lineages multiply by binary fission, as do animal cells. Of these, the ciliate Tetrahymena is known to form an actin ring beneath the division furrow in cytokinesis. Here, we investigated the role of filamentous actin in the cytokinesis of Tetrahymena pyriformis by treating synchronized dividing cells with an actin-inhibiting drug, Latrunculin-A. Video microscopic observation of live cells undergoing cytokinesis was performed, and contrary to expectation, we found that initiation of furrow ingression and its progress are not suppressed under the inhibitory condition of actin polymerization in Tetrahymena cells. We suggest that an actin filament-independent mechanism of binary fission may have been acquired during the evolution in this organism.

In Tetrahymena, besides apparent cell polarity generated by specialized cortical structures, several proteins display a specific asymmetric distribution suggesting their involvement in the generation and the maintenance of cell polarization. One of these proteins, a membrane skeleton protein called fenestrin, forms an antero-posterior gradient, and is accepted as a marker of cell polarity during different cellular processes, such as cell division or oral replacement. In conjugating cells, fenestrin forms an intracytoplasmic net which participates in pronuclear exchange. The function of fenestrin is still unknown. To better understand the role of fenestrin we characterized this protein in an amicronuclear Tetrahymena pyriformis. We show that in this ciliate not only does fenestrin localization change in a cell division-dependent manner, but its mRNA and protein level is also cell cycle-regulated. We determine that the two available anti-fenestrin antibodies, 3A7 and 9A7, recognize different pools of fenestrin isoforms, and that 9A7 is the more general. In addition, our results indicate that fenestrin is a phosphoprotein. We also show that the level of fenestrin in the amicronuclear T. pyriformis and the amicronuclear BI3840 strain of T. thermophila is several times lower than in micronuclear T. thermophila., (Copyright © 2013 Elsevier GmbH. All rights reserved.)

Vibrio fischeri proliferates in a sessile, stable community known as a biofilm, which is one alternative survival strategy of its life cycle. Although this survival strategy provides adequate protection from abiotic factors, marine biofilms are still susceptible to grazing by bacteria-consuming protozoa. Subsequently, grazing pressure can be controlled by certain defense mechanisms that confer higher biofilm antipredator fitness. In the present work, we hypothesized that V. fischeri exhibits an antipredator fitness behavior while forming biofilms. Different predators representing commonly found species in aquatic populations were examined, including the flagellates Rhynchomonas nasuta and Neobodo designis (early biofilm feeders) and the ciliate Tetrahymena pyriformis (late biofilm grazer). V. fischeri biofilms included isolates from both seawater and squid hosts (Euprymna and Sepiola species). Our results demonstrate inhibition of predation by biofilms, specifically, isolates from seawater. Additionally, antiprotozoan behavior was observed to be higher in late biofilms, particularly toward the ciliate T. pyriformis; however, inhibitory effects were found to be widespread among all isolates tested. These results provide an alternative explanation for the adaptive advantage and persistence of V. fischeri biofilms and provide an important contribution to the understanding of defensive mechanisms that exist in the out-of-host environment.

A 'proof-of-concept' version of a software tool for making transparent predictions of acute aquatic toxicity has been developed. It is primarily limited to semi-quantitative predictions in one species, the ciliated protozoan, Tetrahymena pyriformis. A freely available system, 'Eco-Derek', was derived by adapting a well-established, knowledge-based structure-activity and reasoning platform (Derek for Windows, Lhasa Limited). The Derek reasoning code was modified to express potency rather than confidence. Structure-activity relationship (SAR) development utilised a curated version of a published dataset, supplemented with the CADASTER Challenge datasets. Forty-five structural alerts were produced. The dependence on log P was examined for each alert and entered into the system as qualitative reasoning rules specifying the predicted potency as Very Low, Low, Moderate, High or Very High. Evaluation studies showed: (a) moderate accuracy for the training set but low accuracy for an external test set; (b) non-linearity in the toxicity-log P relationship for chemicals without identified structural alerts; (c) insufficient differentiation of substituent effects in some of the reactivity-based structural alerts resulting in too few chemicals predicted with Very High toxicity; and (d) the need for additional structural alerts covering polar narcosis and less common reactive or metabolically activated chemical functionality.

The arsenic metabolism in different biological organisms has been studied extensively. However, little is known about protozoa. Herein, we investigated the cell stress responses of the freshwater ciliate Tetrahymena pyriformis to arsenate toxicity. An acute toxicity assay revealed an 18-h EC(50) arsenate concentration of ca. 40 μM, which caused significant changes in the cell shape, growth and organism mobility. Whereas, under exposure to 30 μM arsenate, T. pyriformis could grow reasonably well, indicating a certain resistance of this organism. Arsenic speciation analysis revealed that 94-98% of the total arsenate in cells of T. pyriformis could be transformed to monomethylarsonic acid, dimethylarsinic acid and a small proportion of arsenite after 18 h of arsenate exposure, thus indicating the major detoxification pathway by arsenic oxidation/reduction and biomethylation. Finally, comparative proteomic analysis unveiled significant changes in the expression of multiple proteins involved in anti-oxidation, sugar and energy metabolism, proteolysis, and signal transduction. Our results revealed multiple pathways of arsenate detoxification in T. pyriformis, and indicated that protozoa may play important roles in the biogeochemical cycles of arsenic., (Copyright © 2012 Elsevier GmbH. All rights reserved.)

The study has demonstrated that anticancer drug 5-fluorouracil causes acute toxicity and interferes with the growth of green microalgae, Scenedesmus vacuolatus. It accumulates in microalgae biomass with bioaccumulation factor of 1.84 × 10(4) and further integrates into the DNA and RNA of microalgae. In addition, the labelled microalgae genome is transferred into protozoan Tetrahymena pyriformis on feeding and is retained in the food vacuoles of predator organisms. This biotransfer of labelled 5-fluorouracil via genomic material was evaluated using radioactivity in Tetrahymena cell pellets though radioactivity did not detect anticancer drug in the genome of the predator organism.

The importance of species diversity to emergent, ecological properties of communities is increasingly appreciated, but the importance of within-species genetic diversity for analogous emergent properties of populations is only just becoming apparent. Here, the properties and effects of genetic variation on predation resistance in populations were assessed and the molecular mechanism underlying these emergent effects was investigated. Using biofilms of the ubiquitous bacterium Serratia marcescens, we tested the importance of genetic diversity in defending biofilms against protozoan grazing, a main source of mortality for bacteria in all natural ecosystems. S. marcescens biofilms established from wild-type cells produce heritable, stable variants, which when experimentally combined, persist as a diverse assemblage and are significantly more resistant to grazing than either wild type or variant biofilms grown in monoculture. This diversity effect is biofilm-specific, a result of either facilitation or resource partitioning among variants, with equivalent experiments using planktonic cultures and grazers resulting in dominance by a single resistant strain. The variants studied are all the result of single nucleotide polymorphisms in one regulatory gene suggesting that the benefits of genetic diversity in clonal biofilms can occur through remarkably minimal genetic change. The findings presented here provide a new insight on the integration of genetics and population ecology, in which diversity arising through minimal changes in genotype can have major ecological implications for natural populations., (© 2011 Blackwell Publishing Ltd.)

The sensitivities of cyclase enzymes adenylate cyclase and guanylate cyclase to glucose and extracellular cAMP were studied in Tetrahymena pyriformis infusoria. Glucose effectively stimulated activities of both cyclase enzymes, while cAMP more effectively stimulated adenylate cyclase. It was shown that [6-(14)C]glucose specifically bound to Tetrahymena pyriformis infusoria at dissociation constant (K(D)) and number of binding sites (B(max)) 43 nM and 7.53 fmol glucose per 100,000 cells and [8-(3)H]cAMP bound at 19 nM and 4.46 fmol cAMP per 100,000 cells, respectively. Hence, glucose and cAMP specifically bound to Tetrahymena pyriformis cells and stimulated activities of cyclases in these infusoria.

1. The interaction between mutualism, facilitation or interference and exploitation competition is of major interest as it may govern species coexistence. However, the interplay of these mechanisms has received little attention. This issue dates back to Gause, who experimentally explored competition using protists as a model [Gause, G.F. (1935) Vérifications expérimentales de la théorie mathématique de la lutte pour la vie. Actualités Scientifiques et Industrielles, 277]. He showed the coexistence of Paramecium caudatum with a potentially allelopathic species, Paramecium bursaria. 2. Paramecium bursaria hosts the green algae Chlorella vulgaris. Therefore, P. bursaria may benefit from carbohydrates synthesised by the algae. Studying endosymbiosis with P. bursaria is possible as it can be freed of its endosymbiont. In addition, C. vulgaris is known to produce allelochemicals, and P. bursaria may benefit also from allelopathic compounds. 3. We designed an experiment to separate the effects of resource exploitation, endosymbiosis and allelopathy and to assess their relative importance for the coexistence of P. bursaria with a competitor that exploits the same resource, bacteria. The experiment was repeated with two competitors, Colpidium striatum or Tetrahymena pyriformis. 4. Results show that the presence of the endosymbiont enables the coexistence of competitors, while its loss leads to competitive exclusion. These results are in agreement with predictions based on resource equilibrium density of monocultures (R*) supporting the idea that P. bursaria's endosymbiont is a resource provider for its host. When P. bursaria and T. pyriformis coexist, the density of the latter shows large variation that match the effects of culture medium of P. bursaria. Our experiment suggests these effects are because of biochemicals produced in P. bursaria culture. 5. Our results expose the hidden diversity of mechanisms that underlie competitive interactions. They thus support Gauses's speculation (1935) that allelopathic effects might have been involved in his competition experiments. We discuss how a species engaged both in competition for a resource and in costly interference such as allelopathy may counterbalance these costs with a resource-provider endosymbiont., (© 2011 The Authors. Journal of Animal Ecology © 2011 British Ecological Society.)

Naturally occurring aroma compounds are able to elicit physiological and migratory responses such as chemotaxis even at nano to femtomolar concentrations in organisms at different levels of phylogeny. Despite the amazing chemical variety of these substances the apparatus by which they can be detected i.e. the chemosensory receptors and the signaling pathways seem to be rather uniform and evolutionary well-conserved. The intracellular signaling process is supposed to be mediated by either cAMP or inositol 1,4,5-trisphosphate. The present work aimed to investigate the chemotactic behavior of 11 odorants that occur naturally in foods and are also used by the industry as additives, on the eukaryotic ciliate Tetrahymena pyriformis. Intracellular signaling pathways that might be activated by these compounds were also investigated. Activation of the phospholipase C (PLC) was measured by FACS and the stimulation of inositol-1,4,5-trisphosphate 3-kinases (IP3K) was measured using two specific inhibitors, wortmannin and LY294002. The strongest chemoattractant character was observed for isoamyl acetate (10(⁻6) M), propyl isobutyrate (10(⁻8) M), isobutyl propionate (10(⁻6) M). The strongest repellent action was exerted by benzyl acetate (10(⁻8) M), furfuryl thioacetate (10(⁻12) M). Our results suggest that Tetrahymena responds in a very sensitive way to slight changes in the molecular structure. According to our study, tracer amounts of solvents do not contribute significantly to the chemotactic profile of the respective odorants. No significant activation of PLC or PI3K could be observed following stimulation with attractant odorants which implies that some other pathways may be involved, hence further investigation is needed.

Spatially separated populations of many species fluctuate synchronously. Synchrony typically decays with increasing interpopulation distance. Spatial synchrony, and its distance decay, might reflect distance decay of environmental synchrony (the Moran effect), and/or short-distance dispersal. However, short-distance dispersal can synchronize entire metapopulations if within-patch dynamics are cyclic, a phenomenon known as phase locking. We manipulated the presence/absence of short-distance dispersal and spatially decaying environmental synchrony and examined their separate and interactive effects on the synchrony of the protist prey species Tetrahymena pyriformis growing in spatial arrays of patches (laboratory microcosms). The protist predator Euplotes patella consumed Tetrahymena and generated predator-prey cycles. Dispersal increased prey synchrony uniformly over both short and long distances, and did so by entraining the phases of the predator-prey cycles. The Moran effect also increased prey synchrony, but only over short distances where environmental synchrony was strongest, and did so by increasing the synchrony of stochastic fluctuations superimposed on the predator-prey cycle. Our results provide the first experimental demonstration of distance decay of synchrony due to distance decay of the Moran effect. Distance decay of the Moran effect likely explains distance decay of synchrony in many natural systems. Our results also provide an experimental demonstration of long-distance phase locking, and explain why cyclic populations provide many of the most dramatic examples of long-distance spatial synchrony in nature., (© 2010 Blackwell Publishing Ltd/CNRS.)

This study examined whether two ciliates could discriminate between equally-sized bacterial prey in mixture and if so, how selectivity might benefit the ciliate population. Live Klebsiella aerogenes, K. ozaenae and Escherichia coli, expressing different coloured fluorescent proteins, were cultured in such a way as to provide populations containing equally-sized cells (to prevent size-selective grazing taking place) and these prey were fed to each ciliate in 50:50 mixtures. Colpidium striatum selected K. aerogenes over K. ozaenae which itself was selected over E. coli. Tetrahymena pyriformis showed no selectivity between K. aerogenes and E. coli but K. aerogenes was selected over K. ozaenae while E. coli was not. This apparent selection of K. aerogenes over K. ozaenae was sustained in ciliate populations with different feeding histories and when K. aerogenes comprised only 20% of the prey mixture, suggesting possible optimal foraging behaviour. The metabolic benefits for selecting K. aerogenes were identified as possibly being an increase in cell biovolume and yield for C. striatum and T. pyriformis, respectively. The mechanism by which these ciliates selected specific bacterial cells in mixture is currently unknown but the use of live fluorescent bacteria, in prey mixtures, offers an exciting avenue for further investigation of selective feeding by protozoa., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Under the AChem paradigm and the programmed self-decomposition (PSD) model, we propose a hierarchical model for the biomolecular covalent bond (HBCB model). This model assumes that terrestrial organisms arrange their biomolecules in a hierarchical structure according to the energy strength of their covalent bonds. It also assumes that they have evolutionarily selected the PSD mechanism of turning biological polymers (BPs) into biological monomers (BMs) as an efficient biomolecular recycling strategy We have examined the validity and effectiveness of the HBCB model by coordinating two complementary approaches: biological experiments using existent terrestrial life, and simulation experiments using an AChem system. Biological experiments have shown that terrestrial life possesses a PSD mechanism as an endergonic, genetically regulated process and that hydrolysis, which decomposes a BP into BMs, is one of the main processes of such a mechanism. In simulation experiments, we compared different virtual self-decomposition processes. The virtual species in which the self-decomposition process mainly involved covalent bond cleavage from a BP to BMs showed evolutionary superiority over other species in which the self-decomposition process involved cleavage from BP to classes lower than BM. These converging findings strongly support the existence of PSD and the validity and effectiveness of the HBCB model.

Many populations show density-dependent growth rates. We suggest that population growth rate may be connected to density through the density dependence of metabolic rate. If metabolic rate is an index of the total biochemical work being done by an organism, then as populations grow and density suppresses metabolic rate, the rate of reproduction should slow and the ability to avoid death should diminish. To test this idea, we grew axenic populations of a single-celled protist, Tetrahymena pyriformis, in laboratory microcosms, and measured metabolic rate and density. We also estimated division (birth) and death rates. The proposed connection was supported by two observations. First, increasing population density suppressed per-capita metabolic rate in accordance with the predictions of a resource-division model. The same pattern was shown with experimentally altered densities. Second, per-capita metabolic rate was positively related to per-capita division rate and negatively related to per-capita death rate. Thus, the particular pattern of population growth and regulation depends on exactly how individuals respond energetically to the density of conspecifics, and how they allocate metabolism to maintenance and production. The physiological basis of population regulation in this system is based on the constraints imposed on the total metabolic work that individual cells can perform.

Spatially synchronized fluctuations in system state are common in physical and biological systems ranging from individual atoms to species as diverse as viruses, insects and mammals. Although the causal factors are well known for many synchronized phenomena, several processes concurrently have an impact on spatial synchrony of species, making their separate effects and interactions difficult to quantify. Here we develop a general stochastic model of predator-prey spatial dynamics to predict the outcome of a laboratory microcosm experiment testing for interactions among all known synchronizing factors: (1) dispersal of individuals between populations; (2) spatially synchronous fluctuations in exogenous environmental factors (the Moran effect); and (3) interactions with other species (for example, predators) that are themselves spatially synchronized. The Moran effect synchronized populations of the ciliate protist Tetrahymena pyriformis; however, dispersal only synchronized prey populations in the presence of the predator Euplotes patella. Both model and data indicate that synchrony depends on cyclic dynamics generated by the predator. Dispersal, but not the Moran effect, 'phase-locks' cycles, which otherwise become 'decoherent' and drift out of phase. In the absence of cycles, phase-locking is not possible and the synchronizing effect of dispersal is negligible. Interspecific interactions determine population synchrony, not by providing an additional source of synchronized fluctuations, but by altering population dynamics and thereby enhancing the action of dispersal. Our results are robust to wide variation in model parameters representative of many natural predator-prey or host-pathogen systems. This explains why cyclic systems provide many of the most dramatic examples of spatial synchrony in nature.

Although the ciliate Tetrahymena is a good model for the study of chemotaxis, its profound motility makes it difficult to monitor intracellular calcium (Ca(2+)) changes induced by chemotactic stimuli. In this study, we report a microfluidic-based chemotaxis system generating directional chemotactic gradients under highly viscous conditions, suppressing T. pyriformis motility, and allowing for the stable confocal imaging of changes in intracellular Ca(2+) in the ciliate. Once the viscous condition was achieved, directional chemical gradients were formed inside the center chamber via the release of N-methyl-d-aspartate (NMDA), a known chemoattractant, from the surrounding chemical reservoirs into the center chamber. As a result, intracellular Ca(2+) in the ciliate increased up to three-fold, and its distribution was skewed in the direction of NMDA stimulation. However, the Ca(2+) in ciliates pretreated with phospholipase C (PLC) or phosphatidylinositol-3-kinase (PI3K) blockers did not increase even after stimulation. Additionally, the PI3K blocker induced the secretion of granules, the size of which was dependent on the concentration of the blocker. Collectively, the results indicate that both PLC and PI3K perform pivotal roles in controlling the levels of intracellular Ca(2+) in T. pyriformis during chemotaxis.

Gravitactic bioconvective patterns created by Tetrahymena pyriformis in a Hele-Shaw apparatus were realized and compared with theoretical results. There were found to be two thresholds for bio-convection development: the first indicates the transition from the diffusion to the steady convection state; the second corresponds to the transition from the steady to the unsteady convection state. The results showed that the Hele-Shaw apparatus may be used as a physical analogy of porous media to study 2D bioconvection, with possible extensions to larger scale biological systems where population growth and distribution are driven by similar bio-physical interactions.

The natural reservoir of Francisella tularensis, the causative agent of tularaemia, is yet to be identified. We investigated the possibility that Francisella persists in natural aquatic ecosystems between outbreaks. It was hypothesized that nutrient-rich environments, with strong protozoan predation, favour the occurrence of the tularaemia bacterium. To investigate the differences in adaptation to aquatic environments of the species and subspecies of Francisella, we screened 23 strains for their ability to survive grazing by the ciliate Tetrahymena pyriformis. All the Francisella strains tested were consumed at a low rate, although significant differences between subspecies were found. The survival and virulence of gfp-labelled F. tularensis ssp. holarctica were then studied in a microcosm experiment using natural lake water, with varying food web complexities and nutrient availabilities. High nutrient conditions in combination with high abundances of nanoflagellates were found to favour F. tularensis ssp. holarctica. The bacterium was observed both free-living and within the cells of a nanoflagellate. Francisella tularensis entered a viable but nonculturable state during the microcosm experiment. When studied over a longer period of time, F. tularensis ssp. holarctica survived in the lake water, but loss of virulence was not prevented by either high nutrient availability or the presence of predators.

The purpose of this study was to develop the structure-toxicity relationships for a large group of 268 substituted benzene to the ciliate Tetrahymena pyriformis using mechanistically interpretable descriptors. The shuffling-adaptive neuro fuzzy inference system (Shuffling-ANFIS) has been successfully applied to select the important factors affecting the toxicity of substituted benzenes to T. pyriformis. The results of the proposed model were compared with the model of linear-free energy response surface and also the principal component analysis Bayesian-regularized neural network (PCA-BRANN) trained using the same data. The presented model shows a better statistical parameter in comparison with the previous models. The results of the model are promising and descriptive. Five descriptors of octanol-water partition coefficient (logP), bond information content (BIC0), number of R-CX-R (C-026), eigenvalue sum from Z weighted distance matrix (SEigZ) and fragment based polar surface area (PSA) selected by Shuffling-ANFIS reveal the role of hydrophobicity, electronic and steric interactions in the mechanism of toxic action. Sequential zeroing of weights (SZW) as a sensitivity analysis method revealed that the hydrophobicity and electronic interactions play a major role in toxicity of these compounds. Satisfactory results (q(2)=0.828 and RMSE=0.348) in comparison with the previous works indicate that the Shuffling-ANFIS-ANN technique is able to model a diverse chemical class with more than one mechanism of toxicity by using simple and interpretable descriptors. Shuffling-ANFIS can be used as powerful feature selection technique, because its application in prediction of toxicity potency results in good statistical and interpretable physiochemical parameters.

Alterations of Hsp70 level were studied in the cells of freshwater ciliate Tetrahymena pyriformis after medium salinity changes. It is shown that ciliates, acclimated to fresh water (0 per thousand) and to salt water of 2 and 10 per thousand have similar constitutive levels of Hsp70 in their cells. Neither pronounced induction of Hsp70, was not decrease of its level, revealed in ciliates after salinity stresses. These data differ from the results obtained while studying euryhaline ciliate Paramecium nephridiatum and strongly freshwater one Paramecium jenningsi. We presume that the differences in the mode of chaperone system reaction of these ciliates species might be connected with different extents of salinity persistence - the least in P. jenningsi, intermediate in T. pyriformis and the most pronounced in P. nephridiatum.

Humans play little role in the epidemiology of Escherichia coli O157:H7, a commensal bacterium of cattle. Why then does E. coli O157:H7 code for virulence determinants, like the Shiga toxins (Stxs), responsible for the morbidity and mortality of colonized humans? One possibility is that the virulence of these bacteria to humans is coincidental and these virulence factors evolved for and are maintained for other roles they play in the ecology of these bacteria. Here, we test the hypothesis that the carriage of the Stx-encoding prophage of E. coli O157:H7 increases the rate of survival of E. coli in the presence of grazing protozoa, Tetrahymena pyriformis. In the presence but not the absence of Tetrahymena, the carriage of the Stx-encoding prophage considerably augments the fitness of E. coli K-12 as well as clinical isolates of E. coli O157 by increasing the rate of survival of the bacteria in the food vacuoles of these ciliates. Grazing protozoa in the environment or natural host are likely to play a significant role in the ecology and maintenance of the Stx-encoding prophage of E. coli O157:H7 and may well contribute to the evolution of the virulence of these bacteria to colonize humans.

This study presents the toxicity data of various nitriles to Pseudokirchneriella subcapitata using a closed algal toxicity testing technique with no headspace. Two different response endpoints, i.e., dissolved oxygen (DO) production and algal growth rate, were used to evaluate the toxicity of nitriles. In general, the DO endpoint revealed higher inhibitory effects than that from algal growth rate. Furthermore, halogen-substituted nitriles were found to be extremely toxic to P. subcapitata. With increasing numbers of the halogen atoms, stronger toxicity was observed. The bromine substitutent also seems to be more toxic than chlorine substitutent. Quantitative structure-activity relationships (QSARs) were established based on the chemicals' Elumo values and hydrophobicity (logK(ow)). Such relationships may thus be useful in predicting the toxicity of other compounds of the same mode of toxic action. Furthermore, for various aquatic organisms, the relative sensitivity relationship is: Pimephales promelas > or = P. subcapitata> Tetrahymena Pyriformis>Daphnia magna>luminescent bacteria (Microtox). The alga, P. subcapitata, was found to be quite sensitive to nitriles compared to other organisms.

I assembled bacterial communities to explore the effects of bacterial diversity on multiple ecosystem functions, including bacterial community biovolume, decomposition of particulate organic matter, and biomass transfer to the next trophic level. The experiment used a two-way factorial design with four levels of bacterial diversity (one to four species) and the absence/presence of a bacterivorous ciliated protist Tetrahymena pyriformis as two main factors, and all possible combinations of the four bacterial taxa nested within each diversity level. Bacterial community biovolume increased as bacterial diversity increased, a result due largely to positive selection effects. Decomposition and consumer abundance, however, were unaffected by bacterial diversity, though both varied among bacterial composition treatments. Negative selection effects, the dominance of species that do not contribute significantly to ecosystem functioning, accounted for the lack of diversity effects on decomposition and consumer abundance. The presence of Tetrahymena reduced bacterial community biovolume but increased decomposition, without altering the diversity-functioning relationships. Decomposition was strongly linked with consumer abundance such that communities supporting larger consumer biomass exhibited higher decomposition rates. This study suggests that if the negative selection effect is common, as it might be when examining ecosystem variables other than biomass (due to the presence of keystone species that can contribute disproportionably to ecosystem functioning relative to their abundances), basic bacteria-mediated ecosystem processes, such as decomposition and energy transfer to the next trophic level, may not increase with bacterial diversity.

High-molecular-weight polyphenols from oolong and black teas increased mitochondrial membrane potential, as measured by a method using ciliated protozoan Tetrahymena and rhodamine 123. These polyphenols, referred to as mitochondrial activation factors (MAFs), were purified from oolong and black teas by solvent extraction and Toyopearl column chromatography. The number-average molecular weights of the MAFs were 9,000 to 18,000, and the weight-average molecular weights were 15,000 to 25,000. The MAFs increased the mitochondrial membrane potential more than catechins did. Treatment of the MAFs with tannase indicated that they contained galloyl residues. When the MAFs were hydrolyzed with HCl-n-BuOH, cyanidin and delphinidin were detected. The partial structure of the MAFs was analyzed by pyrolysis-gas chromatography-mass spectrometry, and nine compounds were identified. These results suggest that MAFs are heterogeneous polymers of flavan-3-ols and flavan-3-ol gallates with intermonomeric linkages of B-ring to B-ring and C-ring to A-ring.

The chemotactic properties of tuftsin (H-TKPR-OH), tuftsin derivatives (H-KPR-OH, H-TKPKG-NH(2), Ac-TKPKG-NH(2)) and TKPKG-based oligotuftsins (T20, T30, T40) were investigated in Tetrahymena pyriformis GL. In contrast to its effects on Mammalia, tuftsin elicited chemorepellent or neutral responses; truncation of the N-terminal part (KPR) led to similar results, though with more neutral effects. The significance of the C-terminal part of the molecule was revealed by the chemoattractant properties of TKPKG, which are nevertheless abolished by acylation. Among the oligotuftsins, T20 and T40 were chemoattractants at higher concentrations (10(-9)-10(-6) M), while T30 had a wide-ranging chemorepellent effect, indicating that chemotaxis is elicited in Tetrahymena only by ligands with optimal physicochemical characters (mass, conformation, etc.). The chemotactic selection data indicated that tuftsin-induced chemotaxis results from fairly short-term signalling in Tetrahymena.

Various studies have documented the associations between mold exposure and effects on health. Mycotoxins, which occur in spores and mold fragments, can be involved in processes that have pathological effects, such as adynamia of the immune system, recurrent infections of the respiratory tract, or asthma. Using Tetrahymena pyriformis, a single-cell organism well established as a suitable model for human respiratory epithelium-cell functionalities, we investigated dose-response relationships of the mycotoxins gliotoxin and penicillic acid. Our study focused on the viability (cell count, MTT assay), energy levels (adenosine-5'-triphosphate content), energy-providing processes (MTT reduction per cell), and cell respiration (oxygen consumption). Both mycotoxins acted as cytotoxins in a dose-dependent manner. Gliotoxin had a stronger inhibitory effect (EC50 0.38 microM) than did penicillic acid (EC50 343.19 microM). The energy-providing processes were not inhibited or were only weakly inhibited under the influence of gliotoxin, whereas penicillic acid caused stimulation of the physiological parameters. Summarizing the results, it is clear that the two investigated mycotoxins must have different modes of action. They are not only different in the strength of their toxic effects but also in a variety of physiological aspects. In addition, T. pyriformis showed differences in its ability to overcome the negative effects of particular mycotoxin exposures., (Copyright 2006 Wiley Periodicals, Inc.)

Discovering why natural population densities change over time and vary with location is a central goal of ecological and evolutional disciplines. The recognition that even simple ecological systems can undergo chaotic behaviour has made chaos a topic of considerable interest among theoretical ecologists. However, there is still a lack of experimental evidence that chaotic behaviour occurs in the real world of coexisting populations in multi-species systems. Here we study the dynamics of a defined predator-prey system consisting of a bacterivorous ciliate and two bacterial prey species. The bacterial species preferred by the ciliate was the superior competitor. Experimental conditions were kept constant with continuous cultivation in a one-stage chemostat. We show that the dynamic behaviour of such a two-prey, one-predator system includes chaotic behaviour, as well as stable limit cycles and coexistence at equilibrium. Changes in the population dynamics were triggered by changes in the dilution rates of the chemostat. The observed dynamics were verified by estimating the corresponding Lyapunov exponents. Such a defined microbial food web offers a new possibility for the experimental study of deterministic chaos in real biological systems.

Tetrahymena pyriformiswas treated with insulin, histamine or serotonin for 30 min and epidermal growth factor (EGF) level was studied inside the cells using specific antibodies and flow cytometry as well as confocal microscopy. The EGF concentration was highly significantly elevated after hormone treatment, regardless of the hormone used. EGF was localized mainly in the cortical region (mucocysts) and in vesicles and this localization did not differ in untreated and treated cells. The results call attention to the possibility of interactions between hormones at unicellular level and points to the presence of a hormonal system in Tetrahymena that includes receptors, hormones and signal transduction pathways as well as hormonal interactions. This could be the basis of further evolution to the hormonal system of multicellulars.

Influence of refrigerated storage on quality of fatty raw material by the example of Pacific herring has been investigated. After freezing and during storage at different temperatures in samples of frozen Pacific herring wedetermined the microbiological parameters, the content of toxic compounds, changes of proteins and accumulation of products of lipids oxidation. In parallel it was determined the quality of frozen herring by method of biotesting using infusorian Tetrachymena pyriformis. It has been established, that during storage of frozen Pacific herring the loss quality of fish raw material takes plase. Results of biotesting completely correlate with the data of chemical analysis under the estimation of fish raw material quality of refrigerated storage.

In ecotoxicology, mechanism-based quantitative structure-activity relationships (QSARs) are usually developed with higher quality than QSARs without regard to toxicity mechanism. Correctly determining the mechanism of a compound, which is not always easy, is required to use mechanism-based QSARs for toxicity prediction. The mechanism determination step may introduce extra errors in addition to the intrinsic prediction errors of mechanism-based QSARs, thus compromising these QSARs' performance compared with QSARs regardless of mechanism. In this study, the mechanism identification-toxicity prediction (MI-TP) approach was compared with the direct toxicity prediction (DTP) approach using a data set containing phenol toxicity to Tetrahymena pyriformis. A statistical mechanism classification model for mechanism prediction, four mechanism-based QSARs and a single QSAR without discriminating between mechanisms were developed for toxicity prediction. Toxicity of phenols in an external data set was predicted following the MI-TP and DTP approaches. Results indicated that the mechanisms of several phenols in the external test set were incorrectly predicted which led to significant over- or under-estimation of their toxicity. Overall, the MI-TP approach did not yield more accurate toxicity prediction than the DTP approach.

Non-ionic surfactants such as Triton X-100 have been widely used in industrial processing and in cleaning products for almost 50 years, being effective and economic emulsifying, wetting agents, dispersants and solubilizers. Cleaning products containing these surfactants are disposed of mainly by discharge into wastewater, which receives biological treatment in wastewater treatment systems. However, surface-active agents interact with eukaryotic cell membranes leading to biological damage at high concentrations. Tetrahymena pyriformis was used here as model organism to assess the effects of Triton X-100 through a series of in vitro cytotoxicity tests. Growth rates and morphological changes were, by their simplicity and reproducibility, the simplest toxicological assays. Cytoskeleton analysis seemed to be related with phagocytosis rate. Viability was evaluated by two different tests. Calcein AM/EthD-1 was used to assess T. pyriformis membrane damage during the 48-h experiment. The colorimetric MTT assay proved to be highly sensitive even at very short periods of Triton X-100 exposure. Tests performed in this study included simple and fast bioassays that provide overall information on the morphological and physiological state of cells exposed to different non-lytic and lytic concentrations of Triton X-100.

The chemotactic effects of six formylated, putatively bacterial peptides (fMLP, fMLPP, fMMM, fMP, fMV, and fMS) were studied. From the set of six peptides, only fMLP (one of the most effective chemoattractant peptides in mammals) elicited a significant positive chemotactic response in the eukaryotic ciliate Tetrahymena pyriformis, while the other formylated ligands, e.g. fMMM (which is also effective in mammals), had neutral or antagonistic effects in Tetrahymena. A study of their amino acid sequences points to an, as yet obscure, interaction between C-terminal f-Met and N-terminal aromatic Phe. Some optimal physicochemical characteristics (e.g. solvent exposed area, solubility) of the molecule may be responsible for this special feature of f-MLP at such a low level of phylogeny. This means that the unicellular Tetrahymena is able to select between related molecules, giving high priority to the molecule that is the most chemoattractive in mammals. The results call attention to the possible presence of f-Met receptors at a unicellular level and to the evolutionary conservation of chemotaxis-activating processes.