Alive viruses

Some have argued that the possession of ribosomes is a key ingredient. This draws a neat distinction between viruses and obligate intracellular parasites such as Chlamydia and Rickettsia.

This definition also confers the status of life on mitochondria and plastids, however. The endosymbiosis that led to mitochondria is thought to have given rise to eukaryotic life.

Mitochondria have metabolic activity on which we depend, they have machinery to manufacture proteins and they have genomes. Most would accept that mitochondria are part of a life form, but they are not independent life. I would argue that the only satisfactory definition of life therefore lies in the most critical property of genetic heredity: independent evolution. Life is the manifestation of a coherent collection of genes that are competent to replicate within the niche in which they evolve d.

Viruses fulfil this definition. It is estimated that there are 10 31 virus particles in the oceans — they vastly outnumber all other organisms on the planet. Alive or not, viruses are doing rather well! University of Edinburgh [email protected].

Bamford, D. Evolution of viral structure. Theor Popul Biol 61, — Boyer, M. Phylogenetic and phyletic studies of informational genes in genomes highlight existence of a 4 th domain of life including giant viruses. Moreira, D. Ten reasons to exclude viruses from the tree of life. Nat Rev Microbiol 7, — and associated commentary. Nasir, A. For example, a DNA virus called polyomavirus is commonly used in laboratories to study how viruses cause cancer. But understanding such infections is hugely important to humankind.

Viruses have been disregarded in other ways, too. Consider the tree of life, a model and research tool used to depict evolution through time.

Viruses are routinely left off, including in popular versions such as the Interactive Tree of Life. Without viruses, one cannot fully understand the mechanisms of evolution, says Hill. Viruses are wildly abundant. They infect all cellular life, from single-celled bacteria to elephants, and they are especially dense in the ocean, where they work as a gigantic recycling network, ripping apart 20 percent of the bacteria and other microbes there each day to release tons of carbon, which is then used by other microorganisms to grow.

Viral DNA is transmitted not only from one viral particle to its progeny, but also to other viruses and other species. Because of this, viral genetic sequences have permanently taken up residence in the genomes of all organisms, including ours, and we rely on them. Viral DNA is required for the formation of the mammalian placenta; it is crucial in the growth of early embryos; and the human innate immune system is made up, in part, of ancient viral proteins.

When a person is fighting COVID, they are doing it with the help of viruses that colonized our cells long ago. Viruses are not a missing branch of the tree of life; they are woven into every limb and leaf.

Scientists may always dispute whether viruses are alive or not, but they can hopefully agree on the importance of viruses to life as we know it. Scientists and journalists share a core belief in questioning, observing and verifying to reach the truth.

Science News reports on crucial research and discovery across science disciplines. So while determining if viruses are alive is definitely a complicated issue, what is certain is all of these perspectives will continue to change and grow over time.

In our next blog posting on viruses , we will take a look at some origins of the viruses that we deal with, and how they've made their mark in the fossil record.

Edmonds, Molly. Wessner, D. Nature Education 3 9 Biodiversity Blog. Are Viruses Alive? Friday, 27 March Nicole L Elmer. Illustration: Nicole Elmer Viruses are remarkably diverse. Austin Spring Insects: Crane Flies. But one thing that scientists have struggled to agree on is whether or not viruses are alive. After all, they can't survive or replicate without a host cell, and due to their rapidly changing genes, scientists have never been able to work out how or when they evolved.

Now a study by researchers in the US has managed to complete the first viral tree of life, and it suggests that not only are viruses alive, they're also really, really old, and they share a long evolutionary history with cells. The confusion about viruses is a result of their unique life cycle. Specifically the fact that they can't metabolise nutrients, and they don't contain the proteins needed to copy their own DNA and RNA - instead they invade other animals' cells and use their equipment to do it for them.