On Food Vacuoles inTetrahymena pyriformisGL

Stimulated Raman Scattering Microscopy Reveals Bioaccumulation of Small Microplastics in Protozoa from Natural Waters

Microplastics (MPs) are pollutants of global concern, and bioaccumulation determines their biological effects. Although microorganisms form a large fraction of our ecosystem's biomass and are important in biogeochemical cycling, their accumulation of MPs has never been confirmed in natural waters because current tools for field biological samples can detect only MPs > 10 μm. Here, we show that stimulated Raman scattering microscopy (SRS) can image and quantify the bioaccumulation of small MPs (<10 μm) in protozoa. Our label-free method, which differentiates MPs by their SRS spectra, detects individual and mixtures of different MPs (e.g., polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polystyrene, and poly(methyl methacrylate)) in protozoa. The ability of SRS to quantify cellular MP accumulation is similar to that of flow cytometry, a fluorescence-based method commonly used to determine cellular MP accumulation. Moreover, we discovered that protozoa in water samples from Yangtze River, Xianlin Wastewater Treatment Plant, Lake Taihu and the Pearl River Estuary accumulated MPs < 10 μm, but the proportion of MP-containing cells was low (∼2-5%). Our findings suggest that small MPs could potentially enter the food chain and transfer to organisms at higher trophic levels, posing environmental and health risks that deserve closer scrutiny.

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.

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.

ZnO nanoparticles interfere with top-down effect of the protozoan paramecium on removing microcystis

Under intensive human activity, sewage discharge causes eutrophication-driven cyanobacteria blooms as well as nanomaterial pollution. In biological control of harmful cyanobacteria, top-down effect of protozoan has great potentials for removing cyanobacterial populations, degrading cyanotoxins, and improving phytoplankton community. ZnO nanoparticles as a kind of emerging contaminants have attracted increasing attention because of wide application and their high bio-toxicity effects on reducing the ingestion of aquatic animals including Paramecium, thereby possibly disturbing top-down control of cyanobacteria. Therefore, this study investigated the effects of ZnO nanoparticles at environmental-relevant concentrations on the protozoan Paramecium removing toxic Microcystis. Results showed Paramecium effectively eliminated all the Microcystis, despite exposure to ZnO nanoparticles. However, their ingestion rate was significantly reduced at more than 0.1 mg L^-1 ZnO nanoparticles, thereby delaying Microcystis removal. Nevertheless, at 0.1 mg L^-1 ZnO nanoparticles, the time to Microcystis extinction decreased compared to the group without ZnO nanoparticles, because Microcystis populations were reduced under this circumstance, while ingestion rate of Paramecium was unaffected. Furthermore, ZnO nanoparticles obviously accumulated in food vacuoles of Paramecium, and the size of nanoparticles aggregates and zinc concentrations in Paramecium were increased with ZnO nanoparticles concentrations. At the end of experiment, these food vacuoles were not dissipated. Overall, these findings suggest that ZnO nanoparticles impair protozoan top-down effects through reducing Microcystis and ingestion rate as well as disturbing functions of their digestive organelles, and highlight the need to consider the interfering effects of environmental pollutants on cyanobacterial removal efficiency by protozoans in natural waters.

Establishing a High-Throughput Locomotion Tracking Method for Multiple Biological Assessments in Tetrahymena

Protozoa are eukaryotic, unicellular microorganisms that have an important ecological role, are easy to handle, and grow rapidly, which makes them suitable for ecotoxicity assessment. Previous methods for locomotion tracking in protozoa are largely based on software with the drawback of high cost and/or low operation throughput. This study aimed to develop an automated pipeline to measure the locomotion activity of the ciliated protozoan Tetrahymena thermophila using a machine learning-based software, TRex, to conduct tracking. Behavioral endpoints, including the total distance, velocity, burst movement, angular velocity, meandering, and rotation movement, were derived from the coordinates of individual cells. To validate the utility, we measured the locomotor activity in either the knockout mutant of the dynein subunit DYH7 or under starvation. Significant reduction of locomotion and alteration of behavior was detected in either the dynein mutant or in the starvation condition. We also analyzed how Tetrahymena locomotion was affected by the exposure to copper sulfate and showed that our method indeed can be used to conduct a toxicity assessment in a high-throughput manner. Finally, we performed a principal component analysis and hierarchy clustering to demonstrate that our analysis could potentially differentiate altered behaviors affected by different factors. Taken together, this study offers a robust methodology for Tetrahymena locomotion tracking in a high-throughput manner for the first time.

Assessing the Environmental Effects Related to Quantum Dot Structure, Function, Synthesis and Exposure

Quantum dots (QDs) are engineered semiconductor nanocrystals with unique fluorescent, quantum confinement, and quantum yield properties, making them valuable in a range of commercial and consumer imaging, display, and lighting technologies. Production and usage of QDs are increasing, which increases the probability of these nanoparticles entering the environment at various phases of their life cycle. This review discusses the major types and applications of QDs, their potential environmental exposures, fates, and adverse effects on organisms. For most applications, release to the environment is mainly expected to occur during QD synthesis and end-product manufacturing since encapsulation of QDs in these devices prevents release during normal use or landfilling. In natural waters, the fate of QDs is controlled by water chemistry, light intensity, and the physicochemical properties of QDs. Research on the adverse effects of QDs primarily focuses on sublethal endpoints rather than acute toxicity, and the differences in toxicity between pristine and weathered nanoparticles are highlighted. A proposed oxidative stress adverse outcome pathway framework demonstrates the similarities among metallic and carbon-based QDs that induce reactive oxygen species formation leading to DNA damage, reduced growth, and impaired reproduction in several organisms. To accurately evaluate environmental risk, this review identifies critical data gaps in QD exposure and ecological effects, and provides recommendations for future research. Future QD regulation should emphasize exposure and sublethal effects of metal ions released as the nanoparticles weather under environmental conditions. To date, human exposure to QDs from the environment and resulting adverse effects has not been reported.

Bacteria compete with hematite nanoparticles during their uptake by the ciliate Tetrahymena thermophila

Bacterial accumulation of engineered nanoparticles (NPs) result in their transfer along the food chain. However, there are a lot of NPs not associated with bacteria. Whether bacteria, as representative biotic particles, influence the biological uptake of these non-associated NPs in aquatic ecosystems is unclear. In the present study, we examined the effects of four bacterial species on the uptake kinetics of polyacrylate-coated hematite nanoparticles (HemNPs) by the ciliate Tetrahymena thermophila. The HemNPs were well dispersed. Their adsorption on the bacteria was low with negligible uptake by T. thermophila through bacterial ingestion. This result demonstrated the feasibility of examining the effects of bacteria on the uptake of non-associated HemNPs. Our study further showed that all four bacterial species inhibited the uptake of HemNPs by T. thermophila; however, the effects of the bacterial cells on the physiological activities of the ciliate with respect to its uptake of HemNPs were negligible. In the absence of phagocytosis by T. thermophila, none of the bacteria inhibited HemNP uptake. This observation suggested that bacterial cells competed with the HemNPs for uptake via phagocytosis. Therefore, in evaluations of the environmental risks of NPs, their competition with biotic particles should be taken into account.

Importance of protozoa Tetrahymena in toxicological studies: A review

Tetrahymena is a single-cell eukaryotic organism present in all aquatic environments and can easily be maintained in laboratory conditions in a cost-effective manner. This review gives a brief description of the physiology of Tetrahymena, culture handling, and maintenance of Tetrahymena species. The review article focuses on various toxicological bioassays at different biological organizational (biochemical, individual, population, and community) levels. Furthermore, some techniques such as single cell gel electrophoresis (SCGE) and microcalorimetry assay are also available to investigate the effect of xenobiotics on the integrity of DNA and metabolic state of Tetrahymena species respectively. The article also discusses how the general physiology, behavioural activities and different organelles of Tetrahymena could be useful in toxicological studies. The strength and limitations of Tetrahymena over other model organisms are also discussed. This article also provides suggestions to overcome some problems related to toxicity assessment. Various aspects associated with variability in results, toxicity endpoints, characteristics of organisms and responses against xenobiotic substances (old and new emerging toxicants) are considered.

Bacterial Surface Traits Influence Digestion by Tetrahymena pyriformis and Alter Opportunity to Escape from Food Vacuoles

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.

Tetrahymena phagocytic vesicles as ecological micro-niches of phage transfer

The microbial communities in natural environments such as soil, pond water, or animal rumens are composed of a diverse mixture of bacteria and protozoa including ciliates or flagellates. In such microbiomes, a major source of bacterial mortality is grazing by phagocytic protists. Many protists are omnivorous heterotrophs, feeding on a range of different bacterial species. Due to this indiscriminate feeding, different bacterial species can assemble together in the same phagocytic vesicles where they can potentially exchange genetic material. Here we show that Tetrahymena thermophila imports and accumulates phage donor and recipient bacterial strains in its phagocytic vesicles and that under laboratory conditions the ingested bacteria remain viable for ≥2 h. Prophages in the ingested bacteria induce immediately after ingestion, and the released phages are concentrated in the phagocytic vesicles of the ciliate. These phages retain their ability to infect phage-susceptible bacterial strains. As a consequence of being confined within the phagosome, the frequency of lysogen formation in these vesicles increases 6-fold as compared with the bulk solution. Collectively, these observations suggest that T. thermophila aids in dissemination of bacteriophages by accumulating susceptible bacteria and phages in their phagocytic vesicles.

Packaging of Campylobacter jejuni into Multilamellar Bodies by the Ciliate Tetrahymena pyriformis

Campylobacter jejuniis the leading cause of bacterial gastroenteritis worldwide. Transmission to humans occurs through consumption of contaminated food or water. The conditions affecting the persistence of C. jejuniin the environment are poorly understood. Some protozoa package and excrete bacteria into multilamellar bodies (MLBs). Packaged bacteria are protected from deleterious conditions, which increases their survival. We hypothesized that C. jejuni could be packaged under aerobic conditions by the amoeba Acanthamoeba castellanii or the ciliate Tetrahymena pyriformis, both of which are able to package other pathogenic bacteria.A. castellanii did not produce MLBs containing C. jejuni In contrast, when incubated with T. pyriformis,C. jejuni was ingested, packaged in MLBs, and then expelled into the milieu. The viability of the bacteria inside MLBs was confirmed by microscopic analyses. The kinetics of C. jejuni culturability showed that packaging increased the survival of C. jejuniup to 60 h, in contrast to the strong survival defect seen in ciliate-free culture. This study suggests that T. pyriformis may increase the risk of persistence of C. jejuniin the environment and its possible transmission between different reservoirs in food and potable water through packaging.

Ingestion and digestion studies in Tetrahymena pyriformis based on chemically modified microparticles

Recognition of food and, in consequence, ingestion of digestible particles is a prerequisite for energy metabolism in Tetrahymena pyriformis. Understanding why some particles are ingested and digested, whereas others are not, is important for many fields of research, e.g. survival of pathogens in single-celled organisms or establishment of endosymbiotic relationships. We offered T. pyriformis synthetical bovine-serum-albumin (BSA)-methacrylate microparticles of approximately 5.5 μm diameter and studied the ciliates' ingestion and digestion behaviour. Different staining techniques as well as co-feeding with a transformant strain of Escherichia coli revealed that T. pyriformis considers these particles as natural food source and shows no feeding preference. Further, they are ingested at normal rates and may serve as sole food source. A pivotal advantage of these particles is the convenient modification of their surface by binding different ligands resulting in defined surface properties. Ingestion rate of modified microparticles either increased (additional BSA, enzymes) or decreased (amino acids). Furthermore, we investigated glycosylation patterns by lectin binding. By binding different substances to the surface in combination with various staining techniques, we provide a versatile experimental tool for elucidating details on food recognition and digestion that may allow to study evading digestion by pathogens or potential endosymbionts, too.

Long-term exposure of bacterial and protozoan communities to TiO2 nanoparticles in an aerobic-sequencing batch reactor

Titanium dioxide (TiO2) nanopowders at different concentrations (0-50 mg L-1) were injected into an aerobic-sequencing batch reactor (SBR) to investigate the effects of long-term exposure to nanoparticles on bacterial and protozoan communities. The detection of nanoparticles in the bioflocs was analyzed by scanning electron microscopy, transmission electron microscopy, and energy-dispersive x-ray spectroscopy. The SBR wastewater experiments were conducted under the influence of ultraviolet light with photocatalytic TiO2. The intrusion of TiO2 nanoparticles was found both on the surface and inside of the bioflocs. The change of microbial population in terms of mixed liquor-suspended solids and the sludge volume index was monitored. The TiO2 nanoparticles tentatively exerted an adverse effect on the microbial population, causing the reduction of microorganisms (both bacteria and protozoa) in the SBR. The respiration inhibition rate of the bacteria was increased, and the viability of the microbial population was reduced at the high concentration (50 mg L-1) of TiO2. The decreasing number of protozoa in the presence of TiO2 nanoparticles during 20 days of treatment with 0.5 and 1.0 mg L-1 TiO2 is clearly demonstrated. The measured chemical oxygen demand (COD) in the effluent tends to increase with a long-term operation. The increase of COD in the system suggests a decrease in the efficiency of the wastewater treatment plant. However, the SBR can effectively remove the TiO2 nanoparticles (up to 50 mg L-1) from the effluent.

TiO2 nanoparticles act as a carrier of Cd bioaccumulation in the ciliate Tetrahymena thermophila

When nanoparticles can enter a unicellular organism directly, how may they affect the bioaccumulation and toxicity of other pollutants already present in the environment? To answer this question, we conducted experiments with a protozoan Tetrahymena thermophila. The well-dispersed polyacrylate-coated TiO2 nanoparticles (PAA-TiO2-NPs) were used as a representative nanomaterial, and Cd as a conventional pollutant. We found that PAA-TiO2-NPs could get into Tetrahymena cells directly. Such internalization was first induced by low concentrations of Cd, but later suppressed when Cd concentrations were higher than 1 μg/L. Considering its significant adsorption on PAA-TiO2-NPs, Cd could be taken up by T. thermophila in the form of free ion or metal-nanoparticle complexes. The latter route accounted for 46.3% of Cd internalization. During the 5 h depuration period, 4.34-22.1% of Cd was excreted out, which was independent of the concentrations of intracellular Cd and PAA-TiO2-NPs. On the other hand, both free and intracellular Cd concentrations only partly predicted its toxicity at different levels of PAA-TiO2-NPs. This may have resulted from PAA-TiO2-NPs' synergistic effects and the distinct subcellular distribution of Cd taken up via the two routes above. Overall, we should pay attention to the carrier effects of nanoparticles when assessing their environmental risks.

A simple microscopy assay to teach the processes of phagocytosis and exocytosis

Phagocytosis and exocytosis are two cellular processes involving membrane dynamics. While it is easy to understand the purpose of these processes, it can be extremely difficult for students to comprehend the actual mechanisms. As membrane dynamics play a significant role in many cellular processes ranging from cell signaling to cell division to organelle renewal and maintenance, we felt that we needed to do a better job of teaching these types of processes. Thus, we developed a classroom-based protocol to simultaneously study phagocytosis and exocytosis in Tetrahymena pyriformis. In this paper, we present our results demonstrating that our undergraduate classroom experiment delivers results comparable with those acquired in a professional research laboratory. In addition, students performing the experiment do learn the mechanisms of phagocytosis and exocytosis. Finally, we demonstrate a mathematical exercise to help the students apply their data to the cell. Ultimately, this assay sets the stage for future inquiry-based experiments, in which the students develop their own experimental questions and delve deeper into the mechanisms of phagocytosis and exocytosis.

Trophic transfer of nanoparticles in a simplified invertebrate food web

The unique chemical and physical properties of engineered nanomaterials that make them attractive for numerous applications also contribute to their unexpected behaviour in the environment and biological systems. The potential environmental risks, including their impact on aquatic organisms, have been a central argument for regulating the growth of the nanotechnology sector. Here we show in a simplified food web that carboxylated and biotinylated quantum dots can be transferred to higher trophic organisms (rotifers) through dietary uptake of ciliated protozoans. Quantum dot accumulation from the surrounding environment (bioconcentration) was limited in the ciliates and no quantum dot enrichment (biomagnification) was observed in the rotifers. Our findings indicate that dietary uptake of nanomaterials should be considered for higher trophic aquatic organisms. However, limited bioconcentration and lack of biomagnification may impede the detection of nanomaterials in invertebrate species.

The Tetrahymena thermophila phagosome proteome

In vertebrates, phagocytosis occurs mainly in specialized cells of the immune system and serves as a primary defense against invading pathogens, but it also plays a role in clearing apoptotic cells and in tissue remodeling during development. In contrast, unicellular eukaryotes, such as the ciliate Tetrahymena thermophila, employ phagocytosis to ingest and degrade other microorganisms to meet their nutritional needs. To learn more about the protein components of the multistep process of phagocytosis, we carried out an analysis of the Tetrahymena phagosome proteome. Tetrahymena cells were fed polystyrene beads, which allowed for the efficient purification of phagosomes. The protein composition of purified phagosomes was then analyzed by multidimensional separation coupled with tandem mass spectrometry. A total of 453 peptides were identified that resulted in the identification of 73 putative phagosome proteins. Twenty-eight of the proteins have been implicated in phagocytosis in other organisms, indicating that key aspects of phagocytosis were conserved during evolution. Other identified proteins have not previously been associated with phagocytosis, including some of unknown function. Live-cell confocal fluorescence imaging of Tetrahymena strains expressing green fluorescent protein-tagged versions of four of the identified phagosome proteins provided evidence that at least three of the proteins (including two with unknown functions) are associated with phagosomes, indicating that the bulk of the proteins identified in the analyses are indeed phagosome associated.

The Bacillus subtilis spore coat provides "eat resistance" during phagocytic predation by the protozoan Tetrahymena thermophila

Bacillus spores are highly resistant to many environmental stresses, owing in part to the presence of multiple "extracellular" layers. Although the role of some of these extracellular layers in resistance to particular stresses is known, the function of one of the outermost layers, the spore coat, is not completely understood. This study sought to determine whether the spore coat plays a role in resistance to predation by the ciliated protozoan Tetrahymena, which uses phagocytosis to ingest and degrade other microorganisms. Wild-type dormant spores of Bacillus subtilis were efficiently ingested by the protozoan Tetrahymena thermophila but were neither digested nor killed. However, spores with various coat defects were killed and digested, leaving only an outer shell termed a rind, and supporting the growth of Tetrahymena. A similar rind was generated when coat-defective spores were treated with lysozyme alone. The sensitivity of spores with different coat defects to predation by T. thermophila paralleled the spores' sensitivities to lysozyme. Spore killing by T. thermophila was by means of lytic enzymes within the protozoal phagosome, not by initial spore germination followed by killing. These findings suggest that a major function of the coat of spores of Bacillus species is to protect spores against predation. We also found that indigestible rinds were generated even from spores in which cross-linking of coat proteins was greatly reduced, implying the existence of a coat structure that is highly resistant to degradative enzymes.

Feasibility of using GFP-expressing Escherichia coli, coupled with fluorimetry, to determine protozoan ingestion rates

The feasibility of using a live Escherichia coli population, which had been engineered to express the green fluorescent protein (GFP), coupled with fluorimetry, was tested as a means for determining protozoan ingestion rates. Its potential use was based on evidence that once cells are acidified, e.g. in a food vacuole, the fluorescence is lost. Of the 29 protozoa tested, over 85% ingested the GFP-expressing E. coli and a detailed experiment with the ciliate Tetrahymena pyriformis was carried out, principally to assess the performance of the live bacterium against two commonly used surrogate prey, i.e. fluorescently labelled bacteria (FLB) and fluorescently labelled microspheres (FLMs). A decrease in GFP-expressing E. coli fluorescence and, hence, concentration, was recorded by fluorimetry and epifluorescence microscopy, with calculated ingestion rates being equivalent. A higher ingestion rate was determined by counting the number of fluorescent E. coli within the ciliate over 120 s, but this was equivalent to that obtained for the stained E. coli using the same direct method of analysis. However, the ciliate was shown to process the stained and unstained E. coli cells differently, with only the latter resulting in an increase in ciliate abundance.

A community model of ciliate Tetrahymena and bacteria E coli: Part II. interactions in a batch system

Premised on relatively simple assumptions, mathematical models like those of Monod, Pirt or Droop inadequately explain the complex transient behavior of microbial populations. In particular, these models fail to explain many aspects of the dynamics of a Tetrahymena pyriformis-Escherichia coli community. In this study an alternative approach, an individual-based model, is employed to investigate the growth and interactions of Tetrahymena pyriformis and E. coli in a batch culture. Due to improved representation of physiological processes, the model provides a better agreement with experimental data of bacterial density and ciliate biomass than previous modeling studies. It predicts a much larger coexistence domain than rudimentary models, dependence of biomass dynamics on initial conditions (bacteria to ciliate biomasses ratio) and appropriate timing of minimal bacteria density. Moreover, it is found that accumulation of E. coli sized particles and E. coli toxic metabolites has a stabilizing effect on the system.

Processing of food vacuoles in the parasitic ciliate Ichthyophthirius multifiliis after exit from the host

The digestive cycle of the fish parasite Ichthyophthirius multifiliis (Ciliophora) can be divided into three main stages. During stage A the vacuoles are not yet condensed. This stage can be subdivided into an early phase in which food vacuoles contain almost intact fish cells and a later phase in which dense material accumulates at the periphery of the vacuoles. At stage B, food vacuoles attain a very high density, and at stage C the vacuole expands when the membrane pulls away from a condensed mass of substances in digestion. After its exit from the host the parasite encysts and divides, but new food vacuoles are not formed during this phase of the life cycle. Type A vacuoles are the first to disappear after exit from the host. The percentage of type B vacuoles increases during the first few hours of free life, decreasing later when the percentage of type C vacuoles starts to increase. At the end of the division phase, type C vacuoles are the most common. Food-vacuole egestion was observed only 20 h after exit from the host. At the theront stage, food vacuoles were not evident, but small vacuoles with acid phosphatase activity were observed.

Processing of digestive vacuoles in Tetrahymena and the effects of dichloroisoproterenol

The digestive-lysosomal system in Tetrahymena has been extensively studied; however, the various vacuole stages and the existence of a required processing period prior to defecation have not been clearly defined. In this study the presence of such a required processing period and the rate of DV defecation in Tetrahymena thermophila were determined. Like the cycle in Paramecium, a digestive cycle in Tetrahymena consisted of two periods: the processing period was 45 min and the defecation period was approximately 2 h, making the complete cycle approximately 3 h. During the defecation period vacuole egestion followed the kinetics of a first-order rate reaction and had a rate constant of 0.0187/min and a t1/2 of 37 min (82 min into the cycle). Using the naphthol AS-TR phosphate-hexazotized rosanilin method to visualize acid phosphatase activity at the light microscopic level, DVs became positive beginning at 10 min. The number of positive DVs increased to a maximum of 13% when DVs were 20-min old and declined to 5-7% beyond 30 min. Although dichloroisoproterenol (DCI) has been reported by others to stimulate vacuole defecation, we found it inhibited the defecation rate. The extent of inhibition depended on the age of the DVs when exposed to DCI. Vacuole formation was completely blocked in cells preexposed to 40 microM DCI for only 10 min; however, upon further exposure, cells could recover from this inhibition. The time required for complete recovery increased with increasing DCI concentrations. If DCI was given to cells simultaneously with latex beads, it was found to exert a dose-dependent inhibitory effect on DV formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Utilization of iron complexes in an animal cell

The ciliate protozoan Tetrahymena thermophila was grown in synthetic nutrient medium in the absence of the iron chelator citrate. Utilization and toxicity of various iron compounds or complexes in iron-starved cells were assessed from the number of cell doublings obtained within a standard time. The compounds tested included complexes formed between ortho-phosphates and two forms of ferric hydroxides, native and cationized ferritin, and tris-acetylacetonato Fe(III). The ferric hydroxo ortho-phosphate particles are toxic and can be removed from the medium by Millipore filtration. Uptake of ferritin and tris-acetylacetonato-Fe(III) is independent of food vacuole formation and seems to occur by micropinocytosis and by plasma membrane translocation, respectively.