Lesson 12
Discovering Viruses: Even though he couldn't see them, one scientist gave them a name.
Discovering Viruses: Even though he couldn't see them, one scientist gave them a name.
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Not long after founding a colony they name “New Amsterdam” (it will become New York) Dutch settlers are shipping big leaves from America across the ocean to their home in the Netherlands. There the tobacco leaves get processed and turned into a product that becomes very popular. Dutch farmers are soon growing the leaves themselves.
People who are daring or fashionable or just curious begin puffing on fumes from the leaves which are stuffed inside long clay pipes and burned. Indian tobacco (which is what it is called) becomes the rage; some say there are health benefits to smoking. No one knows for sure. Tobacco profits begin turning into gold in the Dutch treasury. Then something happens: a blotchy mosaic-like pattern of live and dead tissue appears on leaves in the tobacco fields. No one wants to smoke those leaves. By the mid-19th century whatever is infecting the crop is destroying the livelihood of Europe’s tobacco farmers and merchants. One of Amsterdam’s bankrupt merchants is named Beijerinck (say buyer-ink and you’ll be close, there is no exact English equivalent of some Dutch vowel sounds). His son, Martinus Willem Beijerinck (1851-1931), happens to be a biologist who, eventually, will found the new Delft School of Microbiology. The younger Beijerinck is eager to find the villain behind the tobacco outbreak. This agricultural calamity is impacting an economy, it commands attention. Near the end of the 19th century, Beijerinck thinks he has found the culprit. Years earlier, in 1864, a French biologist named Louis Pasteur captured the attention of the public when he figured out that heating up milk helped make it safe to drink, a process that came to be known as pasteurization. Pasteur has charisma, people find him and his ideas exciting and attractive. That helps make science popular with a lot of people. Pasteur has been doing work with bacteria; they soon get blamed for most disease (they deserve some, but not all, the blame). About this same time, new technology (especially improved microscopes) is making it possible to study very tiny life forms. A French microbiologist invents a filter with pores even smaller than a bacterium. When a solution containing bacteria is poured through the filter the bacteria get separated out; then the latest magnifying microscopes can be used to bring them into view. But, powerful as these new devices are, there’s a limit to what they can see. And whatever it is that Beijerinck has discovered, it is too small to be seen by the magnifying microscopes of the day. (Electronic microscopes are in the future.) Chemist Adolph Mayer, a young professor at the Agricultural School in the small town of Wageningen, is also among those tackling what is being called Tobacco Mosaic Disease (we now know that TMD also infects tomatoes and some other plants). Mayer realizes that their must be an infection that gets transferred from plant to plant, just as bacterial infections are transferred from person to person. He filters bacteria out of the sap of infected plants. Then he takes that bacteria and injects it into healthy plants. The plants do not get TMD. In a paper written in German in 1886, Mayer is baffled. He is sure the disease is bacterial and he just hasn’t found the right bacterium, but he is wrong: TMD is not bacterial. In Russia, biologist Dmitri Ivanovsky goes further: he injects filtered sap (the bacteria have been removed) into healthy plants. They get TMD. How can that be? He, too, is convinced the infectious agent is a bacterium, but he is wrong. Beijerinck guesses that whatever is causing the infection may not be a bacterium: it may be another entity, one so small it passes right through the filters that trap bacteria. He does an experiment similar to Ivanovsky’s in which he filters sap, removes the bacteria, and injects the bacteria-free liquid into a healthy plant; it soon has TMD. Beijerinck realizes that something in that filtered liquid is multiplying in the cells of the tobacco plant. Whatever it is, the infectious agent will not grow on the Petri dishes used to cultivate bacteria. He finds it only in cells that are dividing, which tells him that this agent needs a host cell in order to reproduce. In Paris, Louis Pasteur is studying another virus, rabies, which can pass from animals to humans. Not sure what it is, he guesses that it might be something so small that there is no 19th century device that will let him, or anyone else of the time, see it. In 1898 Beijerinck guesses that there must be a tiny infectious entity that no one has discovered. He calls it a “virus,” a name he creates from the Latin virulentus (meaning poisonous slime). He figures out that viruses must be at least 100 times smaller than bacteria, which makes them too small to be seen with any optical microscope. Beijerinck is right: viruses exist and are incredibly small. (Consider this: one drop of water can hold 200 million viruses.) We now know that a virus is composed of either DNA or RNA molecules, or sometimes both. It is held together by a protein coat known as a capsid. That’s all there is; there’s no reproductive equipment in a virus. To reproduce itself it must take over the machinery of a living cell. At a time (the 19th century) when all life was defined as cellular and no one knew the role of DNA, these parasites seem beyond the category of the living. We now know viruses are parasites that may carry genes but they need to feed on other life forms. And they evolve faster than anything else known. So, are virus alive? That question will be argued for more than a century until America’s great biologist Carl Woese (1928-2012), rejects both sides of this scientific fray. For Woese (who is arguably America’s greatest biologist), life is a communal thing, “there is a continuity of energy flux, communication, informational transfer from the genome up through cells, community, virosphere, and environment.” And that, he says, “renders academic” the debate “is a virus dead or alive?” The biological world is interdependent says Woese and you can't consider organisms in isolation from each other. For Woese, Beijerinck was “arguably the greatest microbiologist in the discipline’s history… " and his study of bacteria one in which, “the organismal community and its environment were a paramount concern...For Beijerinck the organism was no mere sum of its parts.” Rather, it was a study in “the profound problem of the origin of life itself.” But in the 19th century these ideas are out-of-step with the times. As for Beijernick, he can’t understand why everyone isn’t as fascinated with lab work as he is. He screams at his students when they make errors, which doesn’t make him popular. If he has a life outside the laboratory, no one knows of it. He never marries and lives with his two sisters. Beijernick’s insights are so far ahead of his time that most of his peers don’t even consider them. A few do pay attention: in 1905 he is awarded the prestigious Leeuwenhoek Medal. In his acceptance speech, he talks of “the profound problem of the origin of life itself.” Could that origin be related to the very tiny creatures that fascinate him? In the 20th century, crystallization techniques and electron microscope images––developed by the American scientist Wendell Stanley––prove the existence of viruses. In 1935, four years after Beijernick’s death, the viral agent he discovered gets formally named Tobacco Mosaic Virus. In the 21st century (2011), journalist Carl Zimmer writes, “The science of virology is still in its early, wild days. Scientists are discovering viruses faster than they can make sense of them.” In a book titled, A Planet of Viruses, Zimmer talks of viral activity as “a bustling trade network, its webs reaching back billions of years.” Today some biologists see viruses as a window into the origin of life. One of them, Patrick Fortere at the Pasteur Institute in Paris, says that life has four foundational domains: archaea, bacteria, eukaryote, and viruses. But some biologists don't agree with the inclusion of viruses into what for them is a big three. Something else: Tobacco is now seen as a noxious weed and smoking tobacco as an addiction. Some of that smoke may be blowing in a new direction. Tobacco is under consideration as a biofuel. And modified tobacco virus is being tested to treat cancers and genetic disorders. |
Martinus Beijerinck in his lab.
(This story, like the others posted here, is copyrighted by Joy Hakim. It is part of a new book on life science that, like Aristotle Leads the Way, Newton at the Center, and Einstein Adds A New Dimension, published by Smithsonian Books, combines narrative nonfiction with conventional science.)
Symptoms of Tobacco Mosaic Disease
searching science: Is science just for experiments and lab work? We don't think so. We believe that reading and thinking are essential. Something else: science is not just for scientists. Its stories make it important and understandable to everyone, not just future scientists.
Here's a quote to consider. What is this author saying? Can you put it in your own words? 
SARS-CoV-2
"No longer can microbes, plants, or animals be seen as passive recipients and passers on of active genes. They have hidden genetic resources that they can draw upon in times of stress. . .they can evolve extremely quickly in response to changing environmental circumstances. The molecular geneticists have, by their discoveries. . .set off into undiscovered territory, in a new phase of the human effort to understand what life is all about.." Nigel Calder, Magic Universe * Do some research into the field of molecular genetics. Pick a person, or a subject that interests you and find out all you can about it. Write a scholarly paper on what you find. Share that paper with your teachers: Or: write a poem about viruses. Or a song. |