We Continue to Discover new Viruses – Viruses

by Vincent Racaniello, PhD

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    00:00 Yet when we look, we find new viruses and one of the big areas of virology today is virus discovery and in this example, a number of virologists went to Antarctica. And there is a lake there called Limnopolar lake, which is frozen most of the time, they went and drilled a hole in the ice and sampled some of the water, brought it back to the laboratory and they were able to find many new viruses. They identified 10,000 different species and some of them were brand-new, some of them they had never seen before and you can do this kind of virus discovery almost anywhere. In water of any sort, saltwater or freshwater, ocean or lake, you can do it in dirt, you can do it in animals and people do this all the time and they are constantly discovering new viruses and as I've said at the beginning of our discussion, we find them everywhere and they are very, very many of them.

    01:00 Now you may ask, why should I care about discovering new viruses, aren't we content with the ones that we know about? And there are a few reasons why this is important. First of all, viruses outnumber cells on the planet by at least 10 to 1. There are way more viruses than anything else. They have the greatest biodiversity on earth, that means their genetic information is more varied than all of the cells put together and in fact that may even make sense because if we think that viruses were here first on the planet, everything evolved from them.

    01:32 It turns out that viruses play a really big role in the cycling of elements on the Earth's surface. Here is an example of that. In the oceans we believe that phytoplankton are food for larger organisms, which we call grazers, which are in turn eaten by larger organisms, in this case fish. As these organisms die, either the phytoplankton or the grazers or the carnivores, they are decomposed and they become what we call particulate dissolved organic matter. These are very small particles derived from these animals, they sink down into the ocean and there, at lower depths, bacteria use these to grow. They're heterotrophic, they need to take up compounds from the environment and they produce carbon dioxide among other things that's used for life. We now learned that viruses are a key part of these cycles, viruses help kill the phytoplankton, they help kill the grazers, they help kill the bacteria and liberate organic matter much faster than we ever knew. In fact, every second in the ocean, there are this many infections. That's one with a lot of zeros after it, per second, so we're turning over a lot of matter in the oceans. So basically viruses drive global cycling of the major elements, like phosphorus and sulfur.

    03:04 Of course viruses as I've told you are beneficial, but they can also be pathogens, they can cause disease, so that's why we want to discover new viruses, to see what is out there on earth, to see if perhaps we should be worrying about some other viruses that we don't know about.

    03:21 Now at this point you may be very confused and puzzled, there are so many viruses, how can I remember them, what can I do? Well in fact, let me give you two facts that will help you simplify the order to viruses. The first is that all viral genomes are obligate molecular parasites. That's a little bit of a variation on the explanation I gave you earlier, which I've said viruses are an obligate intracellular parasite. The genome itself is a molecular parasite, because it needs to get in the cell in order to reproduce.

    03:53 So just remember that, the genome has to be compatible with what is going on in the cell, it can't be something totally different, otherwise the cell would not be able to replicate.

    04:03 So immediately that restricts the way the genome can be. The second fact is that all viruses have to make messenger RNA that can be translated by the host ribosome. No virus encodes a translation system that can make proteins, only the cells have that. So on this slide the green squiggly lines are messenger RNAs that are produced by cellular machinery. These have to be translated into proteins by the host cell. So every virus on the planet has to make messenger RNA that can be recognized by the cell. So this very much limits the diversity of viruses, it can't do anything crazy, it has to adapt to the way the cell works. And this really helps us to understand the diversity in the virus world.

    04:51 So by listening to this talk today about viruses, I'm hoping that you'll go away with some knowledge about how and when viruses were discovered. I hope you'll understand some of the defining features of viruses and that you will appreciate that viruses are everywhere, they outnumber cellular life. You should also know that there are both good and bad viruses, viruses that help us, viruses that make us sick and I'm sure you'll be able to answer the question: Are viruses alive? Thanks for listening, we'll see you next time.

    About the Lecture

    The lecture We Continue to Discover new Viruses – Viruses by Vincent Racaniello, PhD is from the course Microbiology: Introduction.

    Included Quiz Questions

    1. Bacteria
    2. Protozoans
    3. Viruses
    4. Planktons
    5. Phytoplankton
    1. Viral mRNA
    2. Viral tRNA
    3. Viral Golgi apparatus
    4. Host mRNA
    5. Viral DNA

    Author of lecture We Continue to Discover new Viruses – Viruses

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD

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