Ciliate Tetrahymena Pyriformis Research Articles

New insights into binary mixture toxicology: 2. Effects of reactive oxygen species generated by some carboxylic diesters on marine and freshwater organisms (VIII)

This paper presents the development of toxicity of some saturated and phthalate carboxylic diesters (CDE) quantified by experimentally measured (Mes) and calculated (C) values using the Hydractinia echinata (invertebrate) Toxicity Screening Test System (HeTSTS) and the Köln Model (KM) algorithm. The validity of the investigation model is confirmed by the results for three other aquatic organisms: the ciliate protozoan Tetrahymena pyriformis, the freshwater fish Pimephales promelas and the freshwater crustacean Daphnia magna test systems have shown that the evolution of effectiveness is similar, although the absolute values are different. CDE undergoes rapid, irreversible, selective and abiotic –OH– nucleophilic catalyzed monohydrolysis with the formation of the substrate amphiphilic carboxylate monoester (CME), saturated or phthalate and alcohol (AL) as a xenobiotic (SbX) binary mixture in stoichiometric proportion. The Mes represents the inverse of the logarithm of the diester concentration (molL-1), which determines the 50% reduction in metamorphosis of H. echinata from larva to polyp and is influenced by the saturated carbon atom (Cs) of the molecular substructure involved in monohydrolysis. According to the KM algorithm, Cs is the Elementary Specific Interaction Parameter (ESIP) with a specific and constant toxicity value – identical in different substances – depending on the nature of the organism that allows the calculation of toxicity predictions in C. AL is the fingerprint of the mixture (FP) because it influences the diffusion of CMEs through the cell membrane to cellular receptors (CRs). Generally, the Mes and C, are the predicted ECOSAR and calculated C* values form the Class Regulated Increased Toxicity (CRIT) and Class Regulated Decreased Toxicities (CRDT) series. The use of H. echinata in toxicity determinations is an alternative for the study of the relevant ecological impact of chemical oxidative stress on aquatic organisms and, consequently, on human health.

CHEMICAL COMPOSITION OF BIOLOGICAL PREPARATIONS OBTAINED BY BIOCONVERSION OF PEA AND CHICKPEA SERUM

In this work, we studied the chemical composition of preparations obtained by bioconversion of carotenoid yeast Rhodotorula mucilaginosa of pea and chickpea whey, a secondary product of flour processing into food protein concentrate. In the process of growth, yeast assimilate carbohydrate, nitrogenous components and provided the chemical composition of biological products, allowing them to be attributed to the highest group of fodder yeast. The chemical composition of dry biomass from whey: total protein (Nx6.25) – 58.90–61.29%, fat – 1.20–2.31%, ash elements – 3.53–4.53%, soluble and insoluble fibers – 9.33–10.35% and 22.52–26.04%, respectively. The biological effectiveness of lipids based on the study of the fatty acid composition of lipids: the ratio of saturated:monoenoic:polyenoic fatty acids is characterized by the predominance of unsaturated acids – 17 : 62 : 18 in the pea preparation and 18 : 33 : 45 in the chickpea preparation. The pea preparation contains 2.4 times more ω-6 of linoleic acid, the chickpea preparation contains 2.5 times more oleic acid. The biological effectiveness of lipids was also confirmed by chromatographic analysis of the composition of carotenoid components, which is represented by phytoin, torulene, β-carotene, torularodine and phytoin. There is no phytoin in the chickpea biological product, but β-carotene is present in a larger amount (2.8 times). The biological value of biological products with a yield of 0.50–0.54 g/100 cm3 is confirmed by the amount of essential amino acids and their rate (114–278% for pea and 120–242% for chickpea biological products). For both drugs, there is no toxicity in experiments with the ciliate Tetrahymena pyriformis, in the presence of which its active growth is observed. With a pea preparation, the growth factor is 29.1% higher than with distilled water, with a chickpea preparation it is 18.6% higher. In the body of animals, a biologically complete protein with essential amino acids, lipids and carotenoids in the composition of pea and chickpea preparations will actively participate in the metabolism not only as energy materials, but also as biologically active components in the synthesis of hormones, vitamins and other vital compounds.

The Potassium Channel Blocker β-Bungarotoxin from the Krait Bungarus multicinctus Venom Manifests Antiprotozoal Activity

Protozoal infections are a world-wide problem. The toxicity and somewhat low effectiveness of the existing drugs require the search for new ways of protozoa suppression. Snake venom contains structurally diverse components manifesting antiprotozoal activity; for example, those in cobra venom are cytotoxins. In this work, we aimed to characterize a novel antiprotozoal component(s) in the Bungarus multicinctus krait venom using the ciliate Tetrahymena pyriformis as a model organism. To determine the toxicity of the substances under study, surviving ciliates were registered automatically by an original BioLaT-3.2 instrument. The krait venom was separated by three-step liquid chromatography and the toxicity of the obtained fractions against T. pyriformis was analyzed. As a result, 21 kDa protein toxic to Tetrahymena was isolated and its amino acid sequence was determined by MALDI TOF MS and high-resolution mass spectrometry. It was found that antiprotozoal activity was manifested by β-bungarotoxin (β-Bgt) differing from the known toxins by two amino acid residues. Inactivation of β-Bgt phospholipolytic activity with p-bromophenacyl bromide did not change its antiprotozoal activity. Thus, this is the first demonstration of the antiprotozoal activity of β-Bgt, which is shown to be independent of its phospholipolytic activity.

Intracellular bioaccumulation of the rare earth element Gadolinium in ciliate cells resulting in biogenic particle formation and excretion

Ciliates are abundant unicellular organisms capable of resisting high concentrations of metal ions in the environment caused by various anthropogenic activities. Understanding the cellular pathways involved in resistance to and detoxification of elements is required to predict the impact of ciliates on environmental element cycles. Here, we investigated the so far unknown process of tolerance, cellular uptake and bioaccumulation of the emerging rare earth element gadolinium (Gd) in the common ciliate Tetrahymena pyriformis. Gd treatment results in the intracellular formation and excretion of biogenic Gd-containing particles. This cellular process effectively removes dissolved Gd from the organic growth medium by 53.37% within 72 h. Based on light and electron microscopic observations, we postulate a detoxification pathway: Cells take up toxic Gd3+ ions from the medium by endocytosis, process them into stable Gd-containing particles within food vacuoles, and exocytose them. Stable biogenic particles can be isolated, which are relatively homogeneous and have a diameter of about 3 µm. They consist of the elements Gd, C, O, P, Na, Mg, K, and Ca. These findings broaden the view of metal ion accumulation by protists and are of relevance to understand environmental elemental cycles and may inspire approaches for metal recovery or bioremediation.

Uptake without inactivation of human adenovirus type 2 by Tetrahymena pyriformis ciliates.

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 log10 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.

Aeromonas salmonicida intraspecies divergence revealed by the various strategies displayed when grazed by Tetrahymena pyriformis.

Worldwide, Aeromonas salmonicida is a major bacterial pathogen of fish in both marine and freshwater environments. Despite psychrophilic growth being common for this species, the number of characterized mesophilic strains is increasing. Thus, this species may serve as a model for the study of intraspecies lifestyle diversity. Although bacteria are preyed upon by protozoan predators, their interaction inside or outside the phagocytic pathway of the predator can provide several advantages to the bacteria. To correlate intraspecies diversity with predation outcome, we studied the fate of psychrophilic and mesophilic strains of A. salmonicida cocultured with the ciliate Tetrahymena pyriformis. A total of three types of outcome were observed: digestion, resistance to phagocytosis, and pathogenicity. The psychrophilic strains are fully digested by the ciliate. In contrast, the mesophilic A. salmonicida subsp. pectinolytica strain is pathogenic to the ciliate. All the other mesophilic strains display mechanisms to resist phagocytosis and/or digestion, which allow them to survive ciliate predation. In some cases, passage through the phagocytic pathway resulted in a few mesophilic A. salmonicida being packaged inside fecal pellets. This study sheds light on the great phenotypic diversity observed in the complex range of mechanisms used by A. salmonicida to confront a predator.

Study of biscuit safety with sugar subtitutes by biotesting

The article was presented the results of biotesting of oat biscuit with sugar and sugar substitutes with using of the ciliate Tetrahymena pyriformis. It has been established that oat biscuit with sugar substitutes is safe for the test culture, as it has a positive effect on growth rates, vital activity and development of living cells on the generations of ciliates.

Microbial Grazers May Aid in Controlling Infections Caused by the Aquatic Zoosporic Fungus Batrachochytrium dendrobatidis.

Free-living eukaryotic microbes may reduce animal diseases. We evaluated the dynamics by which micrograzers (primarily protozoa) apply top-down control on the chytrid Batrachochytrium dendrobatidis (Bd) a devastating, panzootic pathogen of amphibians. Although micrograzers consumed zoospores (∼3 μm), the dispersal stage of chytrids, not all species grew monoxenically on zoospores. However, the ubiquitous ciliate Tetrahymena pyriformis, which likely co-occurs with Bd, grew at near its maximum rate (r = 1.7 d–1). A functional response (ingestion vs. prey abundance) for T. pyriformis, measured using spore-surrogates (microspheres) revealed maximum ingestion (Imax) of 1.63 × 103 zoospores d–1, with a half saturation constant (k) of 5.75 × 103 zoospores ml–1. Using these growth and grazing data we developed and assessed a population model that incorporated chytrid-host and micrograzer dynamics. Simulations using our data and realistic parameters obtained from the literature suggested that micrograzers could control Bd and potentially prevent chytridiomycosis (defined as 104 sporangia host–1). However, simulated inferior micrograzers (0.7 × Imax and 1.5 × k) did not prevent chytridiomycosis, although they ultimately reduced pathogen abundance to below levels resulting in disease. These findings indicate how micrograzer responses can be applied when modeling disease dynamics for Bd and other zoosporic fungi.

Дослідження гострої токсичності та впливу мийно-дезінфекційного засобу «Аргомол» на культуру інфузорій Tetrahymena pyriformis

Detergents and disinfectants for sanitation of milking equipment and dairy equipment must have a wide range of antimicrobial activity and provide a proper cleaning effect. At the same time, they must meet high standards of environmental safety and non-toxicity. The article presents data on the parameters of acute toxicity of the new detergent-disinfectant “Argomol”, based on lactic acid, “Katamine AB”, polyhexamethylene guanidine hydrochloride and colloidal silver solution, as well as the toxicity of the tool, which was determined using the express method of Tetrachymena pyriformis. The acute toxicity of the means and its working 0.5% solution in tentative and detailed experiments on white mice was determined and the median lethal dose (DL50) was determined by the method of G. Kerber. It was found that the DL50 of the means in white mice for intragastric administration when calculated by the method of G. Kerber is 4250 mg/kg body weight, and 0.5% of its solution — more than 11000 mg/kg body weight, i. e. according to SOU 85.2-37-736:2011 “Veterinary drugs. Determination of acute toxicity”, this indicates that the means belongs to the IV class of toxicity, which combines low-toxic substances. The results of research on the effect of the new detergent-disinfectant “Argomol” on the culture of ciliates Tetrahymena pyriformis are presented. It was found that the detergent-disinfectant “Argomol” in concentrations of 0.02–0.5% at exposures of 1–10 min did not show toxic effects on the ciliate Tetrahymena pyriformis. Toxicological studies on ciliates suggest that the detergent-disinfectant “Argomol”, when used in the recommended doses and exposures, can be used for sanitation of milking equipment and dairy equipment, as it is environmentally friendly and low-toxic.

A natural language processing approach based on embedding deep learning from heterogeneous compounds for quantitative structure-activity relationship modeling.

Over the past decade, rapid development in biological and chemical technologies such as high-throughput screening, parallel synthesis, has been significantly increased the amount of data, which requires the creation and the integration of new analytical methods, especially deep learning models. Recently, there is an increasing interest in deep learning utilization in computer-aided drug discovery due to its exceptional successful application in many fields. The present work proposed a natural language processing approach, based on embedding deep neural networks. Our method aims to transform the Simplified Molecular Input Line Entry System format into word embedding vectors to represent the semantics of compounds. These vectors are fed into supervised machine learning algorithms such as convolutional long short-term memory neural network, support vector machine, and random forest to build up quantitative structure-activity relationship models on toxicity data sets. The obtained results on toxicity data to the ciliate Tetrahymena pyriformis (IGC50 ), and acute toxicity rat data expressed as median lethal dose of treated rats (LD50 ) show that our approach can eventually be used to predict the activities of chemical compounds efficiently. All material used in this study is available online through the GitHub portal (https://github.com/BoukeliaAbdelbasset/NLPDeepQSAR.git).

Screening Snake Venoms for Toxicity to Tetrahymena Pyriformis Revealed Anti-Protozoan Activity of Cobra Cytotoxins

Snake venoms possess lethal activities against different organisms, ranging from bacteria to higher vertebrates. Several venoms were shown to be active against protozoa, however, data about the anti-protozoan activity of cobra and viper venoms are very scarce. We tested the effects of venoms from several snake species on the ciliate Tetrahymena pyriformis. The venoms tested induced T. pyriformis immobilization, followed by death, the most pronounced effect being observed for cobra Naja sumatrana venom. The active polypeptides were isolated from this venom by a combination of gel-filtration, ion exchange and reversed-phase HPLC and analyzed by mass spectrometry. It was found that these were cytotoxins of the three-finger toxin family. The cytotoxins from several cobra species were tested and manifested toxicity for infusorians. Light microscopy revealed that, because of the cytotoxin action, the infusorians’ morphology was changed greatly, from teardrop-like to an almost spherical shape, this alteration being accompanied by a leakage of cell contents. Fluorescence microscopy showed that the fluorescently labelled cytotoxin 2 from cobra N. oxiana was localized mainly at the membrane of killed infusorians, indicating that cytotoxins may kill T. pyriformis by causing membrane rupture. This work is the first evidence of the antiprotozoal activity of cobra venom cytotoxins, as demonstrated by the example of the ciliate T. pyriformis.

Experimental Listeria\u2013Tetrahymena\u2013Amoeba food chain functioning depends on bacterial virulence traits

BackgroundSome pathogenic bacteria have been developing as a part of terrestrial and aquatic microbial ecosystems. Bacteria are consumed by bacteriovorous protists which are readily consumed by larger organisms. Being natural predators, protozoa are also an instrument for selection of virulence traits in bacteria. Moreover, protozoa serve as a “Trojan horse” that deliver pathogens to the human body. Here, we suggested that carnivorous amoebas feeding on smaller bacteriovorous protists might serve as “Troy” themselves when pathogens are delivered to them with their preys. A dual role might be suggested for protozoa in the development of traits required for bacterial passage along the food chain.ResultsA model food chain was developed. Pathogenic bacteria L. monocytogenes or related saprophytic bacteria L. innocua constituted the base of the food chain, bacteriovorous ciliate Tetrahymena pyriformis was an intermediate consumer, and carnivorous amoeba Amoeba proteus was a consumer of the highest order. The population of A. proteus demonstrated variations in behaviour depending on whether saprophytic or virulent Listeria was used to feed the intermediate consumer, T. pyriformis. Feeding of A. proteus with T. pyriformis that grazed on saprophytic bacteria caused prevalence of pseudopodia-possessing hungry amoebas. Statistically significant prevalence of amoebas with spherical morphology typical for fed amoebas was observed when pathogenic L. monocytogenes were included in the food chain. Moreover, consumption of tetrahymenas fed with saprophytic L. innocua improved growth of A. proteus population while L. monocytogenes-filled tetrahymenas provided negative effect. Both pathogenic and saprophytic bacteria were delivered to A. proteus alive but only L. monocytogenes multiplied within amoebas. Observed differences in A. proteus population behaviour suggested that virulent L. monocytogenes might slow down restoration of A. proteus ability to hunt again and thus restrict the size of A. proteus population. Comparison of isogenic bacterial pairs that did or did not produce the haemolysin listeriolysin O (LLO) suggested a role for LLO in passing L. monocytogenes along the food chain.ConclusionsOur results support the idea of protozoa as a means of pathogen delivery to consumers of a higher order and demonstrated a dual role of protozoa as both a “Trojan horse” and “Troy.”

Structure–activity relationship (SAR) study of some aliphatic and aromatics carboxyl– and α–amino–C–phosphonates congeneric esters and Schiff derivatives using a developed Köln–model (Hydractinia echinata Toxicity Screening Test System. VI.)

The toxicity development process of the studied Carboxylic− (R1–[C(O)–OR2]n) (n = 1–4), and α–Amino–C–Phosphonates ({R1–CH[(O)P(OR2)2]}n–R3) (n = 1–2) esters is based on the Congenericity Principle and is quantified by the measured values (Mes) using the scientifically developed Köln–Model and Hydractinia echinata Toxicity Screening Test System (HeTSTS). The process consists of two successive steps: i) hydrolysis of the esters in the seawater alkaline medium (pH 8.2) with the formation of the xenobiotic substrate (SbX) consisting of the binary acid–alcohol mixture and ii) their interaction with the cellular receptors (R). In both series of esters, the results indicate, within the combination of the electronic effects, the steric effects, the possible hydrogen bonds, and so on, the clear and well–defined influence of the number of alcoholic carbon atoms (R2) on the Mes values as Class Regulated Increased Toxicity. The approach was also successfully applied and confirmed by published data in what concerns the similarly carboxylic esters for the ciliate protozoan Tetrahymena pyriformis (T. pyriformis) and the freshwater fish Pimephales promelas (P. promelas) as Toxicity Screening Tests Systems (Tp–PpTSTS’s). Based on this research model, there is a possibility of making predictions of toxicity values with respect to these systems for substances not tested yet. Since the hydrolysis of natural or anthropogenic esters requires an important solvation of the formed ions, its importance to its aquatic surrounding environment is directly due to the action of the reaction products.

Class Regular–Increased– and Class Iso–Toxicity, the two clearly defined and recognisable forms of the phenomenon. A developed Köln–Model (Hydractinia echinata Test–System. V.) study

According to the currently developed Köln–Model based on Hydractinia echinata Test–System (HeTS), the methodical toxicity investigations conducted with amphiphilic and non–amphiphilic singular derivatives with homo– and heteronomous segmentation from 20 different classes, reveals that the effectiveness noted M (mol/L) are characteristic for the Aromatic Basis of Toxicity (ABT) model, for the Class Regular–Increased Toxicity (CRIT) and for Class Iso–Toxicity (CIT), respectively. The phenomenon of toxicity is the result of monovalent interaction between the larval cellular receptor (R) of the marine colonial hydroid H. echinata organism and the xenobiotic substrate (SbX) with the molecular aggregate transitional–complex (RSbX) formation and the information–signal generation (SI), according to the Dual Causality Principle that biological phenomena are simultaneously determined by genetic programs and physics laws. The SI consists of chemical (SIch) and electromagnetic (SIem) components, and is directly responsible for the simultaneous onset of the metamorphosis quantified by the M toxicity values and the metabolizing process of the SbX, with the formation of the reaction products (P). The CRIT, respectively CIT approach was also successfully applied to published data obtained with the ciliate protozoan Tetrahymena pyriformis (T. pyriformis), the freshwater fish Pimephales promelas (P. promelas), the freshwater crustacean Daphnia magna (D. magna) and the marine bacterium Vibrio fischeri (name Aliivibrio fischeri) test–systems (TS’s).

Complete Genome Sequence of Oyster Isolate Vibrio vulnificus Env1.

ABSTRACTVibrio vulnificus, a ubiquitous inhabitant of coastal marine environments, has been isolated from a variety of sources. It is an opportunistic pathogen of both marine animals and humans. Here, the genome sequence of V. vulnificus Env1, an environmental isolate resistant to predation by the ciliate Tetrahymena pyriformis, is reported.

CHEMICAL ECOLOGY OF SHALLOW WATER OCTOCORALS. OCCURRENCE OF CEMBRANOLIDES IN PSEUDOPLEXAURA AND EUNICEA

Gorgonians of the genus Pseudoplexaura, from a variety of geographical locations, yield crassin acetate as the major cembranolide. The cembranolides found in Eunicea collected at different locations vary. Eunicin is found in Eunicea mammosa from Bimini, and from a number of other locations. Its position isomer Jeunicin, has been found in the Eunicea from Jamaica. Eunicea from Curacao yields an epimer ot eunicin, Cueunicin, while that from Puerto Rico yields Eupalmerin acetate, and Peunicin occurs in Eunicea collected off Panama. The cembranolides are toxic to various aquatic organisms. They inhibit ciliary action in the ciliate Tetrahymena pyriformis, and in the larvae of the nudibranch Phestilla sibogae.

Estimation of the Toxicity of Different Substituted Aromatic Compounds to the Aquatic Ciliate Tetrahymena pyriformis by QSAR Approach.

Nowadays, quantitative structure–activity relationship (QSAR) methods have been widely performed to predict the toxicity of compounds to organisms due to their simplicity, ease of implementation, and low hazards. In this study, to estimate the toxicities of substituted aromatic compounds to Tetrahymena pyriformis, the QSAR models were established by the multiple linear regression (MLR) and radial basis function neural network (RBFNN). Unlike other QSAR studies, according to the difference of functional groups (−NO2, −X), the whole dataset was divided into three groups and further modeled separately. The statistical characteristics for the models are obtained as the following: MLR: n = 36, R2 = 0.829, RMS (root mean square) = 0.192, RBFNN: n = 36, R2 = 0.843, RMS = 0.167 for Group 1; MLR: n = 60, R2 = 0.803, RMS = 0.222, RBFNN: n = 60, R2 = 0.821, RMS = 0.193 for Group 2; MLR: n = 31 R2 = 0.852, RMS = 0.192; RBFNN: n = 31, R2 = 0.885, RMS = 0.163 for Group 3, respectively. The results were within the acceptable range, and the models were found to be statistically robust with high external predictivity. Moreover, the models also gave some insight on those characteristics of the structures that most affect the toxicity.

Optical biosensor based on the microalga-paramecium symbiosis for improved marine monitoring

Unprecedented increases in anthropogenic pollution of marine environments have made the development of sensitive, cheap, and adaptable early-warning systems absolutely crucial for on-site monitoring of chemical contaminants. Biosensors based on microalgae cells might constitute a promising and cost-effective alternative for environmental analyses since they capable of providing rapid toxicity information in the case of pollution, while assessing the harmful effects of the contaminants on the ecosystem.In this work, an optical biosensor, based on an array of algal biomediators, has been developed to monitor relevant marine pollutants. A pre-study was performed to select the most suitable biomediator for measurements of pesticides in marine water. The potential of the algae-protozoa symbiotic association between Chlorella vulgaris and the ciliate Tetrahymena pyriformis as a sensitive biomediator for biosensor development was assessed, showing enhanced resistance to marine water salinity compared to free-living algae strains. The symbiotic strain was entrapped in calcium-alginate within newly developed fluidic flow cells with integrated detectors for real-time detection of marine pollutants by fluorescence analysis of photosynthetic photosystem II. The biosensor response was examined in the presence of three commonly found pesticides—simazine, atrazine and diuron—alone or in combination, and the results were compared by liquid chromatography-mass spectrometry. The limits of detection for the three herbicides were 1.35, 0.44, and 0.25 μg/L respectively, and 0.13 μg/L for the mixture.In summary, an autonomous integrated symbiotic association of paramecium-chlorella-based biosensor was successfully developed for real-time monitoring of marine water and evaluation of biotoxicity.

Synergistic Interactions within a Multispecies Biofilm Enhance Individual Species Protection against Grazing by a Pelagic Protozoan.

Biofilm formation has been shown to confer protection against grazing, but little information is available on the effect of grazing on biofilm formation and protection in multispecies consortia. With most biofilms in nature being composed of multiple bacterial species, the interactions and dynamics of a multispecies bacterial biofilm subject to grazing by a pelagic protozoan predator were investigated. To this end, a mono and multispecies biofilms of four bacterial soil isolates, namely Xanthomonas retroflexus, Stenotrophomonas rhizophila, Microbacterium oxydans and Paenibacillus amylolyticus, were constructed and subjected to grazing by the ciliate Tetrahymena pyriformis. In monocultures, grazing strongly reduced planktonic cell numbers in P. amylolyticus and S. rhizophila and also X. retroflexus. At the same time, cell numbers in the underlying biofilms increased in S. rhizophila and X. retroflexus, but not in P. amylolyticus. This may be due to the fact that while grazing enhanced biofilm formation in the former two species, no biofilm was formed by P. amylolyticus in monoculture, either with or without grazing. In four-species biofilms, biofilm formation was higher than in the best monoculture, a strong biodiversity effect that was even more pronounced in the presence of grazing. While cell numbers of X. retroflexus, S. rhizophila, and P. amylolyticus in the planktonic fraction were greatly reduced in the presence of grazers, cell numbers of all three species strongly increased in the biofilm. Our results show that synergistic interactions between the four-species were important to induce biofilm formation, and suggest that bacterial members that produce more biofilm when exposed to the grazer not only protect themselves but also supported other members which are sensitive to grazing, thereby providing a “shared grazing protection” within the four-species biofilm model. Hence, complex interactions shape the dynamics of the biofilm and enhance overall community fitness under stressful conditions such as grazing. These emerging inter- and intra-species interactions could play a vital role in biofilm dynamics in natural environments like soil or aquatic systems.

Predicting skin sensitization potential of organic compounds based on toxicity enhancement to Tetrahymena pyriformis, fathead minnow, and Daphnia magna

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 (Te) 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 Te to sensitization, were SNAr > SN1 > MA. These results indicated that toxicity bioassays are useful tools and that Te could be a useful parameter that might be applied to predict skin sensitization.