字幕表 動画を再生する 英語字幕をプリント Humans have mapped nearly all of the land on earth, explored the deepest oceans, stepped foot on the moon, and sent probes to the planets and beyond. But there's a whole world that is left largely unexplored... the microbial world. There's an enormous amount of unidentified microorganisms living within animals, plants, and even our own bodies. Take the human gut for example: only about 50% of the microbes are identifiable. The other 50% don't match to anything that we know about and I would go so far as to say a substantial fraction of that is what we call “viral dark matter”. Viral dark matter is the genetic material from viruses that is so different than the sequences of viruses that we know about, that it can't be detected with most conventional methods. In astronomy, dark matter is attributed to certain gravitational observations in the cosmos, like the formation of galaxies. But so far, it can't be detected. And that's a pretty good analogy for what we're studying here right? We can't detect it with any of our reference viruses but we know it exists. We can see it. It has features that are vaguely like a virus. Under a microscope, it looks like a virus, but a closer look at the DNA sequence reveals that it doesn't match anything ever seen before and so scientists can't confirm what it is or what it does. And a lot of it is thought to be yet unidentified viral information. Hundreds of thousands of unknown viruses probably are covering our bodies, in our intestine, on our skin, in our mouth and everywhere else. In fact, viruses are the most abundant biological entity on earth. More than all other organisms combined. But most of them are harmless. Some, called bacteriophages or phages for short, infect bacteria that live in us and can actually be good for your health. In the same way that fluctuating bacterial populations are important for our health and well-being, the viruses that infect those bacteria are of importance as well. And so viruses are undoubtedly essential for life as we know it on the planet and probably for the persistence of human populations. But there are challenges with identifying and even categorizing some of them as viruses. They're so genetically diverse that two similar looking viruses from the same family, might actually have almost nothing in common. There's an interesting term called polyphyletic, which means, for example, children might want to put whales and say fish into the same category. But from the perspective of evolution, it's very clear that say fish and whales represent distinct forms of life that have come to look similar to each other through various sorts of forces. It may very well be that some of these different viral forms of life are not related to each other, in which case even using the word virus to link them all together might in some ways be misclassification. But identifying and classifying this stuff could help us understand the cause of certain cancers, infections, and even prevent a pandemic. We have learned, for example, that a range of cancers are caused by previously unknown transmissible agents, whether it be cervical cancer, the vast majority of which is caused by human human papilloma virus, HPV. It's also the case for certain gastric cancers, stomach cancers. As we start to uncover the diversity of living things that have the potential to infect us, or perhaps even more likely the sort of bacteria that are so profoundly important in our microbiome, we have the capacity of identifying agents that perhaps cause chronic diseases. And that's exactly what researchers at the National Cancer Institute have done. They were able to catalogue thousands of new viruses in hopes of aiding human health. At first, the team sampled humans and animals in hopes of understanding two specific families of viruses that are associated with cancer. But as they isolated these viruses, they uncovered many more DNA sequences that hadn't been recorded before – viral dark matter. This is kind of where all labs are at this point. We go fishing for the things that we like. And then we get this giant pile of other things. And it's not possible for one person to hand curate 5000 entities. Instead of just ignoring these new DNA sequences, they developed software that makes sharing new viral DNA information easier. Called Cenote-Taker, which is freely available online for others to use, it can automatically annotate virus DNA in a way that's compliant with public databases, making understanding data and sharing findings easier than ever. And now that our tool's available, they can easily take their virus genomes, curate them and annotate them and share them easily with all the other researchers. And so then, God forbid there is another outbreak or pandemic, it's gonna be easy for researchers to find that sequence in humans to know exactly where it was previously... in which animals. We're hoping that basically by rendering the dark matter visible, it just makes it so that if there's a disease association, somebody is going to see it rather than just ignoring it. Although these additional viruses are a small fraction of the millions of unknown viruses that are thought to exist, adding to databases that virologists share is a small step towards preventing and treating health issues. I think it's quite exciting that there is so much that is unknown. Understanding these things has a deep capacity to help us understand our origins, the nature of what life is, the diversity of forms that life can exist in, and to help place us in the broader context of what it means to be alive and what our place in living world really means.