A Voice for Protists


Breaking down the microbiology world one bite at a time

A Voice for Protists

Today, you often hear about countless different microorganisms, like bacteria, that shape our world in helpful and harmful ways. Lactobacillus shirota, Staphylococcus aureus, Clostridium botulinum — the list goes on. Still, it hardly surprises anyone that we rely on microbes to protect ourselves from disease, make cheese, and break down dead plants and animals with ease. But, what about another type of existing  microorganism  —  one that impacts our environments just as much as bacteria? One that accounts for bacterial-and-viral-unrelated phenomena?

Welcome to the Protista kingdom: an empire of misfits. Scientists classify them as wildly diverse eukaryotes that fail to fit in anywhere else with their bacterial, plant, animal, or fungal counterparts. Find unicellular or multicellular protists, big or small ones, disease-causing or primary-producing organisms.

As such, scientists have struggled to uncover their true breadth, until recently, through a method called metabarcoding. Metabarcoding uses genetic material (DNA or RNA) to simultaneously identify the different taxa in a sample — particularly useful to manage large-scale diversity. 

Diatom metabarcoding flowchart
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eDNA refers to the environmental DNA from what scientists have sampled and HTS stands for high-throughput sequencing. Essentially, the diagram shows that scientists collect samples from the environment, extract DNA from those samples, use primers to make sense of that DNA, sequence the DNA, then process, and eventually identify different species.

Metabarcoding has revealed protists’ expansive reach and diversity across the world. It has particularly highlighted how marine environments contrast from soil environments: the two have shown little species overlap between them. This highlights protists’ broad range alongside their various functions. Soil environments and communities also show highly rich protist diversity — with trends that only increase over time. In fact, soil ecosystems harbor so much diversity that current data shows they have more unidentified species than in any other marine or freshwater environment.

Thus, metabarcoding presents an opportunity to view a previously invisible world. That said, it still comes with limitations. For example, metabarcoding may fail or struggle to identify certain protists that live in unique environments, e.g., endosymbionts. 

Overall, metabarcoding yields great potential to fully uncover, then discover protists’ breadth in their natural environments and various functions. This helps us understand more about diverse topics such as human health, environmental change and evolution!

Link to the original post: Fabien Burki, Miguel M. Sandin, Mahwash Jamy, Diversity and ecology of protists revealed by metabarcoding, Current Biology, Volume 31, Issue 19, 2021

Featured image: https://commons.wikimedia.org/wiki/File:Paramecium.jpg