July 2022

Yes, you saw that right. The clip below, by Tomas Tyml, shows giant bacterial cells next to a U.S. dime.

Although bacteria are generally so small they can only be seen with powerful microscopes, this single-celled organism averages nearly a centimeter in length.

Discovered by marine biologist Olivier Gros, Thiomargarita magnifica was found around ten years ago on decaying leaves in a Caribbean mangrove. Whereas most bacterial species are about one to two micrometers (microns) long, T. magnifica averages 9,000 micrometers, nearly the size of a human eyelash. The microbe’s massive size raises questions about previously known bacterial traits. Microbes are generally thought to be limited in size due to their lack of compartmentalizationT. magnifica defies that by being a singular cell growing large enough to be visible with the naked eye. However, the microbe’s size is not its only remarkable trait.

Initially thought to be a Eukaryotic fungus, Jean-Marie Volland discovered T. magnifica’s true identity by genetically analyzing the species. T. magnifica is a Prokaryotic cell, but also has traits normally associated with Eukaryotic organisms. Eukaryotic cells contain a nucleus, an enveloped organelle containing DNA. Prokaryotes do not have organelles, and their DNA is free-floating within the cell. T. magnifica blurs the two classifications because their DNA is enclosed within a membrane sac. The sac is not necessarily a nucleus, but still enough to challenge previous boundaries defining the various forms of life.

Additionally, the newly found species contains a second sac, to which scientists attribute the cell’s massive size. The water-filled sac makes up 73% of the organism, pushing cellular components to its outer edge so that molecular diffusion and nutrient intake can easily take place. The membrane-enclosed sacs are similar to organelles, traits only previously associated with Eukaryotes.

Not only is T. magnifica the largest bacterium ever found, but its molecular makeup is astonishing. The discovery of T. magnifica excites scientists as it introduces a new biological configuration.