One of the main reasons I have chosen to get a degree in biology is to learn more about viruses and hopefully get a job in the future working with them. Because of this interest, I’ve chosen to do my blog post on an article about giant viruses; more specifically the mimivirus. I found an article on Nature’s website called Mimivirus: Leading the Way in the Discovery of Giant Viruses fo Amoeba.
In most biology classes I’ve taken so far, there is always a moment during the semester when viruses are brought up and the professor either claims, “they’re not a living thing and are just a piece of nucleic acid wrapped in protein”, or “they are a living thing, and can be pretty complex”. To me, this article shows that viruses are not only living, but can also be very complex and unique compared to everything else.
In 1980’s and 90’s, two scientists named Rowbotham and Birtles, were investigating outbreaks of Legionnaires disease. They were doing this by gathering amoebas that were known to be associated with legionella bacteria. When they took their samples back to their lab, they found that all their amoeba samples contained legionella species bacteria, except for two of them. These two samples had unknown living things inside and were thought to be a new Gram-Positive coccoid bacteria. In 1995 they took their samples of the unidentified species to the D. Rault laboratory, hoping they could identify them with the amplification of the 16S ribosomal DNA. They continuously attempted to amplify and isolate ribosomal DNA from the objects, but couldn’t. From there, they decided to study it a different way using electron microscopy. When they got back the micrographs they found they weren’t dealing with coccoid bacteria, rather, an enlarged double stranded DNA virus that would become known as the mimivirus.
Since discovering the mimivirus, the discussion concerning what qualifies as virus has been heating up. Before the mimivirus, it was thought that viruses were too small to see under a light microscope, and that they were strictly simple structures. When, in fact, the mimivirus is the exact opposite. It is large enough to see under a light microscope and has a genome 1.2Mb long. The genome is not only large, but codes for an assortment of technical pieces, such as a defense mechanism called MIMIVIRE. MIMIVIRE defends against virophages and is very similar to the popular CRISPR-Cas system from bacteria that is repeatedly noted for gene editing.
In addition, the mimivirus is not known to use an infected cells’ nucleus for its replication like other viruses, but instead, uses a viral factory that essentially becomes the cells’ new nucleus. This unique ability has some scientists theorizing that the eukaryotic nucleus may have originated from a virus factory of a larger virus.
Studies on the pathology of the mimivirus in an amoeba indicate that infection begins when the cell takes up the virus through a phagocytic entry. Once the virus is in, it releases its viral factory and starts using the cells machinery to build new viruses. The cells nucleus gets smaller during infection, but it is unclear what causes this, or how/if the nucleus is being used by the virus. The replication cycle for the mimivirus lasts 12 hours after which the new viruses are released through amoeba lysis. Although the pathology of mimivirus in humans hasn’t been studied extensively, it is consistently found in humans and other eukaryotes and has been linked with pneumonia when present.
I enjoyed reading about the mimivirus and learning how it replicates and what unique machinery it codes for. I think that studying viruses like the mimivirus will give us ideas on how to come up with new medications and gene editing therapy. It is also possible that future studies on viruses like the mimivirus will give us ideas on how life started and how we evolved to what we are today.
https://www.nature.com/articles/nrmicro.2016.197#infection-cycle-of-giant-viruses
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