Tetrahymena thermophila

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Vegetative cell with macronucleus and micronucleus labeled with DAPI

Classification

Higher order taxa

Eukaryota; Chromalveolata; Ciliophora; Oligohymenophorea; Hymenostomatida; Tetrahymenidae

Species

Tetrahymena thermophila

Description and Significance

Tetrahymena thermophila is a large, motile, phagocytic, unicellular eukaryote. The organism is about 20x50µm. T. thermophila live in temperate freshwater environments.

Tetrahymena is an essential model organism that has been used in many biochemistry oriented experiments to identify biological phenomena. Currently this organism is being used to study four major issues: cilia biogenesis, telomerase structure and function, small RNA mediated self versus non-self discrimination, and epigenetic inheritance.

Describe the appearance, habitat, etc. of the organism, and why you think it is important.

Genome Structure

T. thermophila contain two nuclei, a macronucleus and a micronucleus. Each has been sequenced[1]. The macronucleus is ultimately derived from the micronucleus. The micronucleus is diploid and contains 5 pairs of chromosomes. The macronucleus contains 45 copies of 275 chromosomes formed by fragmentation, as well as 9000 copies of the rRNA gene. The macronucleus contains 15% less genetic information than the micronucleus, which represents noncoding DNA and transposable elements. The macronucleus is kept intact through asexual reproduction by telomerase activity. Additionally the mitochondrial genome has been sequenced [2].

Cell Structure

Schematic diagrams of the organization of Tetrahymena thermophila

Tetrahymena thermophila has all the basic structures of animal cells (ER, golgi, mitochondria, actin, tubulin etc.) except intermediate filaments. Additionally T. thermophila contain enlarged food vacuoles and a contractile vacuole which aids in regulating osmotic pressure. The cell has 18-21 rows of cilia lining its cell membrane. Food enters the organism through the oral apparatus and exits through the cytoproct.

Metabolism

How it gains energy; what important molecules it produces.

Life Cycle

In lab T. thermophila's generation time is between 2-3 hours. The presence of the two nuclei reflects T. thermophila’s ability to reproduce both sexually and asexually. During vegetative growth the macronucleus is transcribed, translated and transmitted to the next asexual generation by mitosis. Food stress induces T. thermophila to reproduce sexually, producing pronuclei by meiosis of the micronucleus and exchange with a cell of a different mating type. The macronucleus is ultimately derived from the micronucleus.

T. thermophila life cycle

Ecology and Pathogenesis

Habitat; symbiosis; biogeochemical significance; contributions to environment.
If relevant, how does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

References

Orias, E., et al. “Tetrahymena thermophila, a unicellular eukaryote with separate germline and somatic genomes”. Research in Microbiology. 2011. Volume 162. p. 578-586

Eisen, J., et al. “Macronuclear Genome Sequence of the Ciliate Tetrahymena thermophila, a Model Eukaryote”. Public Library of Science. 2006. Volume 4. p. 1620-1642.

Collins, K., and Gorovsky, M. "Tetrahymena thermophila". Current Biology. 2005. Volume 15. p. R317-R318.

Asai, D., and Forney, J. "Tetrahymena thermophila". 1999. Methods in Cell Biology. Volume 62. p. ii-xviii, 3-585.

Martindale, D., et al. "Conjugation in Tetrahymena thermophila". Experimental Cell Research. 1982. Volume 140. p. 227-236.

Author

Page authored by Hannah Pak and Luke Pryke, students of Prof. Jay Lennon at Indiana University.