As nasty as some viruses can be, we can’t live without them. Living within us are types of viruses called phages, meaning bacteria eaters. Our bodies are home to trillions of them. So far, scientists have identified 21,000 species of phages living in our guts. Most of them infect the bacteria, fungi, and other single-celled organisms that live inside us. Some studies suggest that our resident viruses help keep our bodies in balance, preventing any one species from getting out of control and making us sick.
About two years ago I wrote a blog post about a man whose life was saved by treating him with a phage. He had been infected with a “superbug” (bacteria) that no antibiotic could kill. A phage did the job instead.
In the ocean, phages invade microbes at the rate of 100
billion trillion times a second, killing 15 to 40 percent of bacteria in the
world’s oceans every day. The shredded bacteria spill billions of tons of
carbon for other marine creatures to feast on. Some ocean phages carry genes
for photosynthesis, making the microbes they infect do better job of harnessing
sunlight. In the photosynthetic process, the microbes release oxygen. This
means that the oxygen we breathe is brought to us in part by viruses. (Incidentally,
a quart of seawater holds more viruses than all the human beings on the
planet.)
Remnants of a virus that invaded our shrew-like ancestors
more than 100 million years ago live within us today. In other words, the DNA
of viruses are part of our own DNA. Today we carry about a hundred thousand
fragments of viral DNA, which make up eight percent of the human genome. That means you.
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