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.

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.

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.

Effect of difenoconazole fungicide on physiological responses and ultrastructural modifications in model organism Tetrahymena pyriformis

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 IC₅₀ 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.

A biological sensor platform using a pneumatic-valve controlled microfluidic device containing Tetrahymena pyriformis

In this study, we introduce a microfluidic device equipped with pneumatically actuated valves, generating a linear gradient of chemoeffectors to quantify the chemotactic response of Tetrahymena pyriformis, a freshwater ciliate. The microfluidic device was fabricated from an elastomer, poly(dimethylsiloxane) (PDMS), using multi-layer soft lithography. The components of the device include electronically controlled pneumatic microvalves, microchannels and microchambers. The linear gradient of the chemoeffectors was established by releasing a chemical from a ciliate-free microchamber into a microchamber containing the ciliate. The ciliate showed chemotactic behaviours by either swimming toward or avoiding the gradient. By counting the number of ciliates residing in each microchamber, we obtained a precise time-response curve. The ciliates in the microfluidic device were sensitive enough to be attracted to 10 pmol glycine-proline, which indicates a 10(5) increase in the ciliate's known sensitivity. With the use of blockers, such as DL-2-amino-5-phosphonopentanoic acid (APPA) or lanthanum chloride (LaCl3), we have demonstrated that the NMDA (N-methyl-d-aspartate) receptor plays a critical role in the perception of chemoeffectors, whereas the Ca2+ channel is related to the motility of the ciliate. These results demonstrate that our microfluidic chemotaxis assay system is useful not only for the study of ciliate chemotaxis but also for a better understanding of the signal transduction mechanism on their receptors.