Do viruses prey on other viruses?

If there are so many viruses on Earth, what do they use to reproduce?
22 November 2022



I saw online this claim and haven't fact checked it. So take this with a pinch of salt. It says there's an estimated one followed by 31 zeros of individual viruses on earth. Now that's a big number, but as the old saying goes, even fleas have fleas. So are there viruses that prey on viruses?


Jonathan - Yeah. So I think that number is correct. I saw it quoted in nature microbiology too, and I found an interesting fact that if you lay all of the viruses on earth end to end, they would stretch for a hundred million light years.

Chris - I mean, that's really saying something when we're talking about a flu virus which is one 10,000th of a millimeter across. So that's a lot of viruses, isn't it?

Jonathan - Yeah, I think it's so hard to get one's head around both the size of viruses, but also the enormous number of viruses in the world. So, you know, for example, it might be easier to conceptualize. If you take a liter of seawater, it's a hundred billion virus particles in that liter. Or if you take a kilogram of soil from the earth, there's about a trillion. So that's a million million virus particles in just a kilo of soil. It's just absolutely mind blowing. But I think the thing to remember is that animals and plants and fungi, although they dominate our view of what the tree of life is, they only actually kind of represent a tiny, tiny amount of the tree of life. The vast majority of species are bacteria and archaea. So kind of single celled organisms on the whole, and only a few twigs of the tree of life really are made up of complex life like animals, fungi and plants. So I saw some studies where it says that there's less than 10 million species of complex life, but there's about 1 trillion types of bacteria and archaea. So it's really, it's really mind blowing. And you might say, oh, well these are just tiny little insignificant things. But actually, if you took all the bacteria on the planet and weighed the mass of them, they would weigh a hundred times more than all the humans on the planet. So they're still really, really significant. But to come back to the question, the vast majority of viruses are viruses that infect bacteria. So what we call bacteriophage, phages from the Greek to devour. And these actually play an enormously important role in the way the whole ecosystem works because they kill an estimated 20 to 40% of bacteria on the planet every single day. And this allows the world or the ecosystem to maintain its balance. So yeah super important. But viruses can play positive as well as kind of disease carrying roles.

Chris - Well, we talked the other day in our program about tuberculosis, about the use of these bacteria phages to kill those TB bugs. But returning to the question which was are there viruses that prey on viruses? They have been discovered, haven't they? There are so-called viral phages. There are viruses that piggyback on other viruses and infect viruses. So when a virus is growing in a cell, you can get another virus that comes in and gets into the process and steals some of the resources the other virus is making for itself. So it can basically parasitize a parasite. Yeah, so viruses are incredible things, aren't they?

Jonathan - Mind blowing, mind blowing stuff.

Chris - Yeah. Thank you very much, John.


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