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.



Arnaiz O and Sperling L (2011) Paramecium DB in 2011: new tools and new data for functional and comparative genomics of the model ciliate Paramecium tetraurelia. Nucleic Acids Research 39: D632–D636.

Arnaiz O, Cain S, Cohen J and Sperling L (2007) ParameciumDB: a community resource that integrates the Paramecium tetraurelia genome sequence with genetic data. Nucleic Acids Research 35: D439–D444.

Arnaiz O, Goût J‐F, Bétermier M et al. (2010) Gene expression in a paleopolyploid: a transcriptome resource for the ciliate Paramecium tetraurelia. BMC Genomics 11: 547.

Aufderheide KJ (2008) An overview of techniques for immobilizing and viewing living cells. Micron 39: 71–76.

Aufderheide KJ, Daggett P‐M and Nerad TA (1983) Paramecium sonneborni, n. sp., a new member of the Paramecium aurelia species‐complex. Journal of Protozoology 30: 128–131.

Aufderheide KJ, Du Q and Fry ES (1993) Directed positioning of micronuclei in Paramecium tetraurelia with laser tweezers: absence of detectable damage after manipulation. Journal of Eukaryotic Microbiology 40: 793–796.

Aufderheide KJ, Rotolo TC and Grimes GW (1999) Analyses of inverted ciliary rows in Paramecium. Combined light and electron microscopic observations. European Journal of Protistology 35: 81–91.

Aury J‐M, Jaillon O, Duret L et al. (2006) Global trends of whole‐genome duplications revealed by the ciliate Paramecium tetraurelia. Nature 444: 171–178.

Beale GH (1954) The Genetics of Paramecium aurelia. New York: Cambridge University Press.

Beale GH and Preer JR (2008) Paramecium. Genetics and Epigenetics. Boca Raton, FL: CRC Press.

Beisson J (2008) Preformed cell structure and cell heredity. Prion 2: 1–8.

Beisson J, Bétermier M, Bré M‐H et al. (2010) Silencing Paramecium tetraurelia genes by feeding double‐stranded RNA. Cold Spring Harbor Protocols doi:10.1101/pdb.prot5363.

Catania F, Wurmser F, Potekhin AA, Prybós E and Lynch M (2009) Genetic diversity in the Paramecium aurelia species complex. Molecular Biology and Evolution 26: 421–431.

Corliss JR and Daggett P‐M (1983) ‘Paramecium aurelia’ and ‘Tetrahymena pyriformis’: current status of the taxonomy and nomenclature of these popularly known and widely used ciliates. Protistologica 19: 307–322.

Duharcourt S, Keller A‐M and Meyer E (1998) Homology‐dependent maternal inhibition of developmental excision of internal eliminated sequences in Paramecium tetraurelia. Molecular and Cellular Biology 18: 7075–7085.

Epstein LM and Forney JD (1984) Mendelian and non‐Mendelian mutations affecting surface antigen expression in Paramecium tetraurelia. Molecular and Cellular Biology 4: 1583–1592.

Forney JD, Yantiri F and Mikami K (1996) Developmentally controlled rearrangement of surface protein genes in Paramecium tetraurelia. Journal of Eukaryotic Microbiology 43: 462–467.

Galvani A and Sperling L (2000) Regulation of secretory protein gene expression in Paramecium. Role of the cortical exocytotic sites. European Journal of Biochemistry 267: 3226–3234.

Godiska R, Aufderheide KJ, Gilley PH et al. (1987) Transformation of Paramecium by microinjection of a cloned serotype gene. Proceedings of the National Academy of Sciences of the USA 84: 7590–7594.

Gratias A, Lepère G, Garnier O et al. (2008) Developmentally programmed DNA splicing in Paramecium reveals short‐distance crosstalk between DNA cleavage sites. Nucleic Acids Research 36: 3244–3251.

Janetopoulos C, Cole E, Smothers JF, Allis CD and Aufderheide KJ (1999) The conjusome: a novel structure in Tetrahymena found only during sexual reorganization. Journal of Cell Science 112: 1003–1011.

Jerka‐Dziadosz M, Gogendeau D, Klotz C et al. (2010) Basal body duplication in Paramecium: the key role of Bld10 in assembly and stability of the cartwheel. Cytoskeleton 67: 161–171.

Kapusta A, Matsuda A, Marmignon A et al. (2011) Highly precise and developmentally programmed genome assembly in Paramecium requires ligase IV‐dependent end joining. PLoS Genetics 7: e1002049.

Knight RD, Freeland SJ and Landweber LF (2001) Rewiring the keyboard: evolvability of the genetic code. Nature Reviews Genetics 2: 49–58.

Lekomtsev S, Kolosev P, Bidou L et al. (2007) Different modes of stop codon restriction by the Stylonychia and Paramecium eRF1 translation termination factors. Proceedings of the National Academy of Sciences of the USA 104: 10824–10829.

Lepère G, Nowaki M, Serrano V et al. (2009) Silencing‐associated and meiosis‐specific small RNA pathways in Paramecium tetraurelia. Nucleic Acids Research 37: 903–915.

Mayer KM, Mikami K and Forney JD (1998) A mutation in Paramecium tetraurelia reveals functional and structural features of developmentally excised DNA elements. Genetics 148: 139–149.

Meyer E and Keller A‐M (1996) A Mendelian mutation affecting mating‐type determination also affects developmental genomic rearrangements in Paramecium tetraurelia. Genetics 143: 191–202.

Pearson CG and Winey M (2009) Basal body assembly in ciliates: the power of numbers. Traffic 10: 461–471.

Preer JR (1986) Surface antigens of Paramecium. In: Gall JG (ed.) The Molecular Biology of Ciliated Protozoa, pp. 301–339. New York: Academic Press.

Preer JR (1997) Whatever happened to Paramecium genetics? Genetics 145: 217–225.

Preer JR and Preer LB (1984) Endosymbionts of protozoa. In: Krieg NR (ed.) Bergey's Manual of Systematic Bacteriology, vol. I, pp. 795–811. Baltimore: Williams & Wilkins.

Preer JR, Preer LB and Jurand A (1974) Kappa and other endosymbionts in Paramecium aurelia. Bacteriological Reviews 38: 113–163.

Preer LB, Hamilton G and Preer JR (1992) Micronuclear DNA from Paramecium tetraurelia: serotype 51 A gene has internally eliminated sequences. Journal of Protozoology 39: 678–682.

Prescott DM (1994) The DNA of ciliated protozoa. Microbiological Reviews 58: 233–267.

Prescott DM (2000) Genome gymnastics: unique modes of DNA evolution and processing in ciliates. Nature Reviews Genetics 1: 191–198.

Pritchard AE, Seilhamer JJ, Mahalingam R et al. (1990) Nucleotide sequence of the mitochondrial genome of Paramecium. Nucleic Acids Research 18: 173–180.

Rosati G and Modeo L (2003) Extrusomes in ciliates: diversification, distribution and phylogenetic implications. Journal of Eukaryotic Microbiology 50: 383–402.

Shabalina SA and Koonin EV (2008) Origins and evolution of eukaryotic RNA interference. Trends Ecology and Evolution 23: 578–587.

Sonneborn TM (1970) Methods in Paramecium research. Methods in Cell Physiology 4: 241–339.

Sonneborn TM (1975a) The Paramecium aurelia complex of fourteen sibling species. Transactions of the American Microscopical Society 94: 155–178.

Sonneborn TM (1975b) Paramecium aurelia. In: King RC (ed.) Handbook of Genetics, vol. 2, pp. 469–594. New York: Plenum.

Sonneborn TM and Schneller MV (1979) A genetic system for alternative stable characteristics in genomically identical homozygous clones. Developmental Genetics 1: 21–46.

Steele CJ, Barkocy‐Gallagher GA, Preer LB and Preer JR (1994) Developmentally excised sequences in micronuclear DNA of Paramecium. Proceedings of the National Academy of Sciences of the USA 91: 2255–2259.

Vayssié L, Skouri F, Sperling L and Cohen J (2000) Molecular genetics of regulated secretion in Paramecium. Biochemie 82: 269–288.

Vivier E (1974) Morphology, taxonomy and general biology of the genus Paramecium. In: van Wagtendonk WJ (ed.) Paramecium. A Current Survey, pp. 1–89. Amsterdam: Elsevier Scientific.

Wichterman R (1986) The Biology of Paramecium, 2nd edn. New York: Plenum.

You Y, Scott J and Forney J (1994) The role of macronuclear DNA sequences in the permanent rescue of a non‐Mendelian mutation in Paramecium tetraurelia. Genetics 136: 1319–1324.

Zagulski M, Nowak JK, Le Mouël A et al. (2004) High coding density on the largest Paramecium tetraurelia somatic chromosome. Current Biology 14: 1397–1404.

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‐

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

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