SUMMARY: In 2003, scientists discovered that giant viruses infected amoebas. These giant viruses are so big that they were mistaken for bacteria for the longest time. It wasn’t until scientists realized they contained no ribosomal DNA that these organisms were reclassified as viruses. From there, even more giant viruses were discovered. Some of the most well-studied ones include the mimivirus (Mimiviridae) and the marseillevirus (Marseilleviridae). Giant viruses infect amoebas and form virus factories inside the poor protozoan. However, virophages are tiny viruses that can hijack these viral factories and infect giant viruses or stop/slow their replication inside the amoeba. Scientists theorized that these three organisms, amoebas, giant viruses, and virophages, co-evolved together.
LESSON COMMENTS: This is a fascinating topic that highlights many “exceptions to the rule” in biology. For one, giant viruses can be as big, if not bigger, than a bacterium. Second, while we often think of viruses as infectious particles, they too can be infected by other viruses (virophages). And finally, it is possible for a eukaryote, such as the amoeba, to “team up” with a virus (the virophage) to help fight off infections by another virus (the giant virus). This paper can be used in classes covering evolution, cell biology, disease, protein synthesis, biochemistry of DNA and RNA, and genetics.
Diesend, J., Kruse, J., Hagedorn, M., & Hammann, C. (2018). Amoebae, Giant Viruses, and Virophages Make Up a Complex, Multilayered Threesome. Frontiers in cellular and infection microbiology, 7, 527. https://doi.org/10.3389/fcimb.2017.00527