Paramecium

Karl J Aufderheide, Texas A&M University, College Station, Texas, USA

Published online: November 2011

DOI: 10.1002/9780470015902.a0001969.pub3

Members of the genus Paramecium (from the classical Greek, , 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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    book Frankel J (1989) Pattern Formation. Ciliate Studies and Models. New York: Oxford University Press.
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 Web Links
    ePath Paramecium Genome Database. http://paramecium.cgm.cnrs-gif.fr/

Related Sub-Topics:

Composition and Structure of Microbial Cells | Genomes and Chromosomes | Microbial Evolution and Taxonomy | Protozoa
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Article Title: Paramecium
 
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]