Paramecium

Abstract

Members of the genus Paramecium (from the classical Greek, παραμηκησ, oblong or oval‐shaped) are ciliated protozoa with an elongated shape (length approximately three to four times the width), a uniform distribution of cilia over the cell surface and a ciliated oral groove leading from the anterior of the cell to a midventral deep oral cavity. The oral apparatus is shaped like a funnel, with 12 rows of oral cilia in a helical array inside. Each cell has two distinct types of nuclei: one large, transcriptionally active, polycopy macronucleus and one or more small, transcriptionally inactive micronuclei. Many features make paramecia favourable organisms for the study of many cellular/developmental/genetic aspects of cells. Their large size allows microscopic observations as well as microinjections and cell surgery. They show Mendelian and non‐Mendelian inheritance, and several different epigenetic inheritance patterns. The genome of Paramecium tetraurelia has been sequenced and is available for analysis.

Key Concepts:

  • Species of Paramecium are distributed worldwide in freshwater habitats and are easy to cultivate in the laboratory.

  • Morphological differences are not enough to distinguish some species of Paramecium.

  • The genomes of the macronucleus and micronucleus are not identical, even though both are derived from the same zygote nucleus.

  • The genome of Paramecium tetraurelia has been sequenced; 40 000 genes have been identified.

  • Paramecia do not use two of the three ‘stop codons’ for translation termination.

  • The trichocysts of paramecia are examples of a regulated exocytotic process.

  • The cortex of the cell contains the cilia, basal bodies and associated accessory structures.

  • Paramecia can carry a number of different types of endosymbiotic organisms.

Keywords: ciliates; macronucleus; symbiosis; DNA rearrangements; codons

Figure 1.

Diagram of Paramecium caudatum, showing many cellular structures displayed by members of the genus. Cells of this species possess a single ‘compact’ micronucleus with evenly distributed chromatin. Many other species possess two or more tiny ‘vesicular’ micronuclei with unevenly condensed chromatin. All paramecia possess a large polycopy macronucleus whose transcriptional expression determines most of the phenotype of the cell. The cell has a consistent cortical organisation with distinct ventral, dorsal, left and right sides. The oral apparatus defines the ventral side of the cell (on the right side of this diagram); contractile vacuoles (osmoregulatory structures) are located towards the dorsal side.

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Further Reading

Frankel J (1989) Pattern Formation. Ciliate Studies and Models. New York: Oxford University Press.

Görtz H‐D (ed.) (1988) Paramecium. Berlin: Springer.

Grimes GW and Aufderheide KJ (1991) Cellular Aspects of Pattern Formation: The Problem of Assembly. Basel: Karger.

van Wagtendonk WJ (ed.) (1974) Paramecium. A Current Survey. Amsterdam: Elsevier Scientific.

Web Links

Paramecium Genome Database. http://paramecium.cgm.cnrs‐gif.fr/

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How to Cite close
Aufderheide, Karl J(Nov 2011) Paramecium. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001969.pub3]