That frenzy of research has revealed a lot about SARS-CoV-2, but huge questions remain. Looming over them is the biggest question of all: Is the coronavirus alive?
Scientists have been arguing over whether viruses are alive for about a century, ever since the pathogens came to light. Writing last month in the journal Frontiers in Microbiology, two microbiologists at University College Cork named Hugh Harris and Colin Hill took stock of the debate. They could see no end to it. “The scientific community will never fully agree on the living nature of viruses,” they declared.
Tobacco mosaic viruses came to light in 1941, looking like a pile of pipes. Phages squatted atop bacteria, resembling lunar landing modules. Other viruses turned out to have the shape of writhing serpents. Some looked like microscopic soccer balls. SARS-CoV-2 belongs to the coronaviruses, which June Almeida named in 1967 for their halo of spike proteins. They reminded her of a solar eclipse, during which the sun’s corona of gas streams becomes visible.
As scientists like Almeida began seeing viruses in their electron microscopes, biochemists were breaking them down into their parts. It wasn’t just their size that set them apart from life as we knew it. They didn’t play by the same rules as cellular life. Viruses are largely made of proteins, as are we. And yet they don’t carry the factories for building proteins. They don’t have the enzymes required to turn food to fuel, or to break down waste.
The bizarre nature of viruses came to light just as scientists were rewriting their definition of life in the new language of biochemistry. Viruses straddled their definitions. They multiplied, but not by eating, growing, or even reproducing. They simply invaded cells and forced them to do all the work of making new viruses. (...)
In the 1940s scientists began assembling the evidence for the true nature of genes. In humans and all other cellular forms of life, they’re made of double-stranded DNA.
To unlock the information encoded in a gene, a cell makes a matching version from a molecule called RNA. Then it reads the RNA to produce a protein.
Many viruses also use DNA for their genes. Others, like coronaviruses, have genes made of RNA. Viruses, scientists realized, can hijack our cells because they have something profound in common with us: They write their recipes in the language of life. It turned out that those recipes could be exquisitely short. Humans carry 20,000 protein-coding genes. SARS-CoV-2 has 29. Other viruses need 10 or fewer. (...)
The diversity of viruses is also colossal. Some virologists have estimated that there may be trillions of species of viruses on the planet. When virologists find new viruses, they’re often from a major lineage no one knew about before. Ornithologists and bird-watchers get justifiably excited when they discover a species of bird. Imagine what it would be like to discover birds. That’s what it’s like to be a virologist.
How can we exile all this biological diversity from life? To exile viruses also means we have to discount the power that they have over their hosts. SARS-CoV-2 has killed millions of people, thrown the economy into chaos and sent ripples across the planet’s ecosystems and atmosphere. Other viruses cause devastation every day to other species.
In the ocean, phages invade microbe hosts 100 billion trillion times a second. They kill 15 to 40 percent of bacteria in the world’s oceans every day. And out of those shredded bacteria spill billions of tons of carbon for other marine creatures to feast on.
But viruses can also have friendly relationships with other species. SARS-CoV-2 may be killing thousands of people a day, but our bodies are home to trillions of phages even when we’re in perfect health. So far, scientists have identified 21,000 species of phages residing in our guts. More than 12,000 of them came to light in a single study published just this month.
by Carl Zimmer, NY Times | Read more:
Image: NIAID Rocky Mountain Laboratories (RML), U.S. NIH, CC BY-SA
