Microbes 101: Protists

Protists are … complicated, at least from the perspective of the Tree of Life. The term protozoa (“first animal”) was used in the early 1800s in an attempt to classify organisms that were structurally similar to animal cells but did not take on a complex, multicellular form. Over time the classification evolved, and protist, meaning “the first,” was introduced in 1866 to capture a broader, appropriately named group of the “primordial” organisms that were neither plant nor animal. (Protozoan is still used today, but informally.)

You might remember some familiar characters from biology class: Paramecium, Euglena, and of course Amoeba. Protist cells have all the characteristics that other eukaryotic cells have: membrane-bound organelles with discrete functions, including a nucleus containing DNA. But protists do not form a tidy limb on the Tree of Life; they are a polyphyletic group, meaning they’re composed of organisms scattered around the Tree that do not necessarily share a common ancestor. So “protist” is not a strict definition but rather a catch-all term for (generally small) eukaryotic lifeforms that are not easily classified. While it’s difficult to tell you what a protist is, we can tell you that they are not bacteria, animal, plant, or fungus. But they are microbes!

I Contain Multitudes is a multi-part video series dedicated to exploring the wonderful, hidden world of the microbiome. The series is hosted by science writer Ed Yong and produced by HHMI Tangled Bank Studios in association with Room 608.