trillions of viruses in our bodies

Enrique and Gullans in delanceyplace:

“The human virome includes trillions of viruses that live in and on our cells, plus even more that inhabit the bacteria in our microbiome. The virome is poorly understood and could be considered the 'dark matter of nature' and humanity; we know it is there but have a very hard time describing it or knowing what it is doing. The human virome is essentially our fourth genome; it interacts directly and indirectly with our other three genomes. Moreover, like your genome, epigenome, and microbiome, your virome is absolutely unique. Viruses live in our intestines, mouths, lungs, skin, and even in our blood, the latter being only discovered recently. But fret not; given that people are generally healthy day-to-day, the virome overall must be benign, and given the millennia of mutual coexistence, our viromes must provide benefits that we don't yet appreciate.

“Viruses are champions of DNA mutation. A 2013 study of the human gut virome tracked the identities, abundance, and mutations of native viruses in one person over two and a half years. There were 478 relatively abundant viruses, most of which had not been previously identified. A majority of the viruses were bacteriophage, the type that infects bacteria. Eighty percent of the viruses persisted for the entire 2.5 years, but they all mutated, some slowly, some very quickly. In some cases they mutated so fast that the virus would be deemed a new species within the 2.5 years. What came out of the body after symbiosis was very different from what went in. “So viruses, our ubiquitous interlopers, are an important part of our rapid evolution; they carry, exchange, and modify the DNA between cells or from one species to another. They drive evolution at all scales, in bacteria, plants, animals, and humans. The best example of this is the spread of antibacterial-resistance genes from one bacterial organism to its fellow species, and then to other bacteria of all types, in all geographies. Once a beneficial mutation arises in a microbe, viruses help spread it quickly throughout the microbiome and beyond.

More here.