Intracellular distribution of lead in Tetrahymena during continuous exposure to the metal

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.

Tetrahymena pyriformis: a tool for toxicological studies. A review

Among protozoa, Tetrahymena pyriformis is the most commonly ciliated model used for laboratory research. After a brief description of the morphology and biology of Tetrahymena pyriformis, this article focuses on the most important and recent investigations performed with this species in toxicology and ecotoxicology. The methodological features of its culture, and main tests, based on cell growth rate, biochemical markers, behavioral changes and motility, are discussed. Examples of xenobiotics (organic and inorganic substances, pharmaceutical drugs, water pollutants) tested with Tetrahymena pyriformis are also given.

Toxicity and bioaccumulation of lead in marine protozoa communities

The toxicity and bioaccumulation of lead has been studied using marine protozoa communities developed in laboratory microecosystems. The concentrations tested were 500 and 1000 micrograms.L-1 of lead as lead acetate. The protozoan was able to bioaccumulate 27.02-504 micrograms Pb.g-1 dry weight. Bacteria also bioaccumulated lead, but always to a lesser degree than protozoa. Lead caused a significant reduction in the density of protozoa, which could be an indirect response to the cellular increase of lead. On the other hand, the toxicant did not determine a decrease in the number of bacterial cells; this could be due to their capacity to bioaccumulate a lesser amount of lead, the increase in the number of dead cells, and the elimination of their predators by the toxicant. After 120 h, a recovery of the community was observed.

The influence of growth phase and culture conditions of Tetrahymena on effects of cadmium

The batch culture system is used in the majority of toxicity studies employing protozoa and other cell cultures, although it is known that metal toxicity may vary depending on the age and therefore on the physiological state of the culture. The ciliate Tetrahymena was exposed to cadmium during short-term incubations at different stages of the growth cycle. In cultures with cells proliferating at a high rate (log phase cells) the toxicity of cadmium was found to increase with increasing initial cell density. However, in the subsequent stationary growth phase with decreased rate of cell proliferation, the sensitivity against cadmium again decreases. Thus the effect of a given concentration of cadmium depends on the initial cell density of the culture. This effect of cadmium may be explained either by changes in the chemical composition of the culture medium during the growth cycle or by a changed cellular metabolism. Furthermore, it is shown that the cadmium concentration of the medium decreases during prolonged exposure when the cells are grown in batch cultures. Some of the problems associated with the toxicity bioassay performed in a static system may be overcome by using a continuous flow system. In such a system, Tetrahymena can be kept under optimal growth conditions with a generation time of less than 3 h, and any cell density may be maintained for extended periods of time. Furthermore, the cadmium concentration of the medium remained constant during prolonged exposure when maintaining a cell density of about 50 x 10(3) cells/ml. This illustrates the great advantage of using a continuous flow system in such investigations, where for example, long-term adaptations of the organism to a metal may be studied under constant conditions.