What's in a name?
Updated: Jul 21, 2020
Recently, Matias, a friend and the creator of the Microbial Mondays logo, shared an article about how phytoplankton contribute most of the oxygen to the Earth's atmosphere. My response was, stereotypically, "Microbes for the win!", as the term phytoplankton includes microscopic organisms classified as bacteria, plants, and protists. He cleverly replied, "yes technically, but then you could say land plants are protists with extra steps. Wait are we protists with extra features???"
To be honest, he has a point. I remember being thoroughly confused about what it meant to be a 'protist' in my first year biology course. Today, I'll try to answer that question, and why we should even ask it in the first place.
So, let's get started. What are protists? These little guys have always been a tricky bunch, because historically they were often grouped together according to the things they were not. For example, while researching for this blog post, I found one definition of protists as simply beings that are not plants, animals, fungi, or multicellular. I also found more specific, but jargon-heavy definitions, such as, protists are "eukaryotic organisms with unicellular, colonial, filamentous, or parenchymatous organization that lack vegetative tissue differentiation, except for reproduction." But, my favourite definition was as follows: "The popular term protist is retained to describe eukaryotes with a unicellular level of organisation, without cell differentiation into tissues. In other words, protists are single-celled organisms, and those cells do look a fair bit like ours.
But why worry about protists at all? You see, these diverse microbes are everywhere - just like viruses and bacteria. And as you could guess by my opening statement about how phytoplankton, a group of microbes that includes protists, are necessary for providing oxygen on earth, protists are very important for key cycles on our planet. As well as helping maintain oxygen levels, protists also help cycle other nutrients in the sea and on the land. In other words, protists, along with other microbial and multicellular organisms, help maintain healthy flows of materials like carbon, nitrogen, and sulphur, which are essential for life, through ecosystems.
On top of that, protists also have a more personal importance for us humans. Protists are also a part of our intestinal microbiome - they literally live inside us. The presence of certain protists has even been suggested to help shape and maintain a healthy bacterial population in the gut , which could have downstream implications for gut health and immune system functioning.
On the other hand, protists can harm as well as help us. You probably have already heard of some of the more infamous protists, like malaria or African Sleeping Sickness. As a kid growing up in the Middle East, I remember learning the song,
"Beware of the tsetse fly,
The itsy bitsy tsetse fly,
If you see the tsetse better
Run the other way".
Indeed, the tsetse fly is a host of the protist Trypanosoma brucei, which causes sleeping sickness in humans. Turns out I was already singing about protists at the age of eight.
By now, I guess you have gotten the message that Protists are an interesting bunch, both because of their impressive diversity, and their difficulty to pin down as a group. But why do we even bother pinning them down as a group? As Lynn J. Rothschild brilliantly put it,
"A rose may still smell like a rose, but Juliet missed the point. The utility of taxonomic nomenclature lies in the wealth of biological information that it conveys."
Humans are categorizers. As scientists, categorization is part of our job. And if we can describe something, we can start to understand it. The tradition of scientific nomenclature (or name-giving) comes from a quest to understand and define the unknown, to the best of our current ability. Giving a name to a group allows us to, with one word, express and understand that group's similarities and differences to other groups. Sometimes, modern science seems like a downward spiral of more and more detailed names for smaller and smaller groups. It sure felt like that when I started out. But, the trick is, to avoid being overwhelmed by the details, and rather be dazzled and swept away by them. It is only by diving into smaller and smaller categories, with more and more names, that scientists get closer to truths about how the world works.
For now, as far as I can tell, the modern story of protists is still to some extent a complicated web of definitions, with a handful of scientific protagonists (like Lynn J. Rothschild and this professor at the University of Saskatchewan, Canada, who wrote a novel treatise on what it means to be a protist) who are helping to sort it out. But, this confusion and messiness is exciting. It means that the field is still developing, and there is lots of room for new scientists to answer the question we started with: "What does it mean to be a protist?"