The 'Oddball Organism' that Helped Win a Nobel Prize

What lives in freshwater ponds, comes in seven different sexes and helped UCSF’s Elizabeth Blackburn win a Nobel Prize? The answer is the humble Tetrahymena, the single-celled organism that became a model for research into aging. 

A Tetrahymena uses its cilia to swim toward a friend. Video captured by UCSF’s Nikon Imaging Lab

Many modern advances in health and medicine wouldn’t be possible without the tiny creatures that help researchers study life. That’s why Blackburn, PhD, gave a shout out to Tetrahymena when she accepted the Nobel Prize for Physiology or Medicine in 2009. Blackburn was honored for her work discovering telomeres and the telomerase enzyme, now known to play important roles in how and why cells degrade as we age.

Tetrahymena have a large number of short, paired chromosomes that made them ideal candidates for DNA sequencing in Blackburn’s early work. While studying the pear-shaped protozoa in the 1980s, Blackburn found that they were able to shrink and regrow their DNA, a concept that flew in the face of biological tenets of the time. Exploration of that phenomenon led Blackburn and colleagues Jack Szostak and Carol Greider to discover telomeres, the protective string of code at the ends of chromosomes, and telomerase, which protects chromosomes from degrading over time – in humans as well as Tetrahymena.

“If we had not been able to use these seemingly oddball organisms because of the advantages they offered as experimental systems for biological research, I don't know when we would have learned about telomeres and telomerase,” Blackburn said during her Nobel Prize acceptance speech.

Fun facts about Tetrahymena

  • They have two types of nuclei in their single-celled bodies: a larger macronucleus and a smaller micronucleus that contains 5 pairs of chromosomes (humans have 23).
  • Tetrahymena are essentially sexless until mating time, when they morph into one of seven possible sexes that can mate in 21 different combinations.
  • They are covered in hundreds of tiny cilia, the tiny hairs you see wriggling in the video.