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  • Alex Cloherty

Viruses, viruses everywhere! Part II

Last week, in the first edition of the “Viruses, Viruses Everywhere!” series, we talked about a virus that causes disease in humans. This week, we are going to take a look at a different pathogenic (disease-causing) virus, which affected humans in an entirely different way: tobacco mosaic virus.

Tobacco mosaic virus (TMV) was the first virus ever discovered, by the Dutch scientist Martinus Beijerinck. In 1898, Beijerinck got to the bottom of what was causing wide-spread infection of tobacco crops from Colombia to the Netherlands. The disease was baffling scientists of the day, because neither fungus nor bacteria, which had already been discovered and were known to cause other diseases, were responsible for it. The wide-spread infection didn’t affect the health of humans, but it drastically impacted the economy. Back in the 1800s, tobacco was an important cash crop and TMV was causing farmers to go completely out of business. In fact, Beijerinck was just a little too late in identifying the causative agent of the tobacco plant disease: because of TMV, commercial production of tobacco ground completely to a halt in his country.

You might think, “Gosh, this TMV thing sounds bad.” In some ways, it really was. But the devastation of tobacco plants caused by TMV also led to some incredible advances in modern science. In fact, TMV is at the root of the study of viruses. Although Beijerinck was too late to save the Dutch tobacco industry, he did coin the term “virus” and is now considered the father of virology. As a fun fact, Beijerinck is in the (imaginary) hall of microbiological fame with his fellow Dutch scientist Antonie van Leeuwenhoek, who is commonly considered to be the first microbiologist.

TMV was also broadly used as a “model organism”. For instance, TMV was the first virus to have its structure studied, and American scientist Wendell Meredith Stanley received 1/3 of the Nobel Prize in Chemistry in 1946 for his structural studies of TMV. By crystallizing TMV, more or less in the way that we crystallize sugar to make cubes for our coffee, Stanley showed that the virus was not only composed of protein, but also of RNA. But why was Stanley’s work so important?

First of all, Stanley’s virus sugar-cubes were still infectious, which was surprising to scientists. Imagine dehydrating a human, keeping in mind that we are mostly made up of water. You wouldn’t expect a crispy human totally devoid of water to recover very well, right? But this was basically what Stanley had done to the virus, and it was still functional. Stanley’s study nicely illustrated the impressive durability of viruses.

Secondly, studies like Stanley’s eventually showed scientists that viruses were in a class of their own in comparison to all other known life forms. You have probably heard of DNA, hailed as the script behind all life. Well, if you consider viruses to be alive, this isn’t completely true. Not all viruses use DNA – some, like TMV, use RNA instead! For both us eukaryotes as well as the prokaryotic bacteria and archaea, RNA usually only functions as a sort of intermediate between the DNA script and the protein “machines” that DNA encodes. This process of making RNA from DNA, and proteins from RNA is so important to biology that it is referred to as the “Central Dogma”. Discovering that viruses use RNA in the same way that we use DNA was like discovering aliens alive and well on Earth*.

In conclusion, although TMV doesn’t infect humans, it impacted us greatly. It changed the economy of the 1800s, and revolutionized microbiology, which had before only consisted of the study of bacteria and fungi. TMV also taught us about ourselves: it showed us that our way of life, making protein from RNA that is made from DNA, is not the only one.

That’s all for this week’s Microbial Mondays. Last week we discussed a virus that infects humans. Now we’ve finished an exploration of a virus which infects plants. What’s left? Can you guess what organism is infected by next week’s virus?

Until next week – guess away!

- Alex

*If you’re extra sharp this Monday, you might have wondered why I’m talking about DNA when Wendell Meredith Stanley received his Nobel Prize in 1946. DNA wasn’t discovered yet! This part of the significance of Stanley’s findings indeed only became clear well after he received his Nobel Prize, and many other scientists contributed to this understanding of viruses.

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