Tetrahymena, a free-living unicellular eukaryote, is a ciliate considered to be the most highly developed protozoan, because it possesses specialised organelles that perform each of the cell functions. This pear-shaped microorganism (30×50 m) can be found in almost all freshwater environments, including even natural hot springs in which a thermotolerant strain can live. One distinct feature that sets ciliate apart from other multicellular eukaryotes is the possession of two functionally different nuclei – macronucleus, which is transcriptionally active and responsive for the somatic function of cells, and micronucleus, which is transcriptionally silent and serves as germinal nucleus during mating. Tetrahymena grows easily to high density. Its relatively large size, nuclear dimorphism and other unique genetic characteristics make it a good model system to study the molecular, cellular and genetic processes of cells.

Key Concepts:

• Ciliates are unicellular organisms that execute many biological activities observed in multicellular organisms.
  
• Tetrahymena cells can survive under extremely dangerous conditions such as cold, pH alterations and osmotic stress.
  
• Tetrahymena cells possess rapid adaptation machineries to regulate biological processes including cell division, conjugation and cell death against intracellular and extracellular stresses.