Virus luis villarreal

In this regard, viruses resemble seeds more than they do live cells. They have a certain potential, which can be snuffed out, but they do not attain the more autonomous state of life. Another way to think about life is as an emergent property of a collection of certain nonliving things. Both life and consciousness are examples of emergent complex systems. They each require a critical level of complexity or interaction to achieve their respective states.

A neuron by itself, or even in a network of nerves, is not conscious—whole brain complexity is needed. The enucleated cell is akin to the state of being braindead, in that it lacks a full critical complexity. A virus, too, fails to reach a critical complexity. So life itself is an emergent, complex state, but it is made from the same fundamental, physical building blocks that constitute a virus.

Approached from this perspective, viruses, though not fully alive, may be thought of as being more than inert matter: they verge on life. In fact, in October, French researchers announced fi ndings that illustrate afresh just how close some viruses might come. Didier Raoult and his colleagues at the University of the Mediterranean in Marseille announced that they had sequenced the genome of the largest known virus, Mimivirus, which was discovered in The virus, about the same size as a small bacterium, infects amoebae.

Sequence analysis of the virus revealed numerous genes previously thought to exist only in cellular organisms. Some of these genes are involved in making the proteins encoded by the viral DNA and may make it easier for Mimivirus to co-opt host cell replication systems. Impact on Evolution Debates over whether to label viruses as living lead naturally to another question: Is pondering the status of viruses as living or nonliving more than a philosophical exercise, the basis of a lively and heated rhetorical debate but with little real consequence?

I think the issue is important, because how scientists regard this question infl uences their thinking about the mechanisms of evolution. Viruses have their own, ancient evolutionary history, dating to the very origin of cellular life. For example, some viral- repair enzymes—which excise and resynthesize damaged DNA, mend oxygen radical damage, and so on— are unique to certain viruses and have existed almost unchanged probably for billions of years.

Nevertheless, most evolutionary biologists hold that because viruses are not alive, they are unworthy of serious consideration when trying to understand evolution. They also look on viruses as coming from host genes that somehow escaped the host and acquired a protein coat. In this view, viruses are fugitive host genes that have degenerated into parasites. And with viruses thus dismissed from the web of life, important contributions they may have made to the origin of species and the maintenance of life may go unrecognized.

Indeed, only four of the 1, pages of the volume The Encyclopedia of Evolution are devoted to viruses. Of course, evolutionary biologists do not deny that viruses have had some role in evolution.

But by viewing viruses as inanimate, these investigators place them in the same category of infl uences as, say, climate change. Such external infl uences select among individuals having varied, genetically controlled traits; those individuals most able to survive and thrive when faced with these challenges go on to reproduce most successfully and hence spread their genes to future generations.

But viruses directly exchange genetic information with living organisms—that is, within the web of life itself. A possible surprise to most physicians, and perhaps to most evolutionary biologists as well, is that most known viruses are persistent and innocuous, not pathogenic. These viruses have developed many clever ways to avoid detection by the host immune system— essentially every step in the immune process can be altered or controlled by various genes found in one virus or another.

Viruses therefore surely have effects that are faster and more direct than those of external forces that simply select among more slowly generated, internal genetic variations. And unique genes of viral origin may travel, finding their way into other organisms and contributing to evolutionary change. Data published by the International Human Genome Sequencing Consortium indicate that somewhere between and genes present in bacteria and in the human genome are absent in well-studied organisms—such as the yeast Saccharomyces cerevisiae , the fruit fly Drosophila melanogaster and the nematode Caenorhabditis elegans —that lie in between those two evolutionary extremes.

Some researchers thought that these organisms, which arose after bacteria but before vertebrates, simply lost the genes in question at some point in their evolutionary history. Still, viruses have many traits of living things. They are made of the same building blocks. They replicate and evolve. Once inside a cell, viruses engineer their environment to suit their needs — constructing organelles and dictating which genes and proteins the cell makes. Recently discovered giant viruses — which rival the size of some bacteria — have been found to contain genes for proteins used in metabolism, raising the possibility that some viruses might metabolize.

Plus, almost every rule that excludes viruses from the land of the living has its own exceptions. For example, Rickettsia bacteria are classified as living but, like viruses, can multiply only within other cells.

All living things, in fact, rely on other living things. A single rabbit cannot replicate on its own, but a rabbit is definitely alive, right? For these reasons and others, the debate over whether viruses are alive or not continues today.

In , virologists Marc H. Or maybe a virus can be both nonliving and alive. In , biologist Patrick Forterre of the Pasteur Institute in Paris argued that viruses alternate between an inactive state outside a cell and a living, metabolically active state inside a cell that he calls the virocell. For Forterre, viruses are like seeds or spores. They have the potential for action and that potential can be extinguished.

While debates over classification can at times feel frivolous, in reality how we talk about viruses affects how they are researched, treated and eradicated.

Personifying viruses as villains and menaces interferes with a real understanding of evolution and nature, says Colin Hill , an infectious disease specialist at University College Cork in Ireland.

Like that dirt, some scientists consider persistent viral infections as simply a nuisance and therefore not urgent to study. 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. Somewhat exasperated by the Covid models publicly showcased over the last two months, I decided to ring up virologist Luis Villarreal for his perspective.

It is true that it does have protein surrounding the nucleic acid and a lipid around it, like pretty much all RNA viruses. That the virus is not alive is a conservative, old view and not based on our current understanding of an enormous influence in all living entities due to virus activity and virus colonization.

Suzan Mazur : In a previous conversation you told me the following about viruses:. For me the persistence is a big deal. The persistence of Ebola in a bat, for instance, is not an accident. Luis Villarreal : Yes, very much so.

In fact, this is the can of worms now being argued: the origin of this coronavirus. People have pointed to a lab in China as the origin. But that lab actually has been studying bats and viruses with respect to emergence events. In this case, this family of coronaviruses has numerous relationships with bats in China and that part of the world. This long-term relationship—phylogenetic incongruence—means bat and virus frequently co-evolve in the same environment.

Suzan Mazur : And billions of other viruses have found a host in every human—though not usually harmful? Consider the context of coronavirus. A very well studied coronavirus is mouse hepatitis virus. If this hepatitis virus gets introduced by a persistently infected mouse to a colony that has a history of infection, the virus will then move harmlessly from parent to offspring and the offspring will host that virus throughout their lives and transmit it to their offspring.

Introducing a persistently infected mouse into a virgin mouse colony pretty much destroys the capacity of that colony to reproduce. So it is consequential. Suzan Mazur : Thank you.

Villarreal did postdoctoral research in virology with Nobel laureate Paul Berg at Stanford University. Some hold the view that there is a consensus sequence within the virus, which they term the master fittest type. However, experiments contradict this view and indicate that the quasispecies has within it components that oppose replication of the virus itself.

It has members not participating in the replication of the infectious virus. It has polymerase that has an added feature. It has what we call an error and repair function, which limits the ability of the genome to some degree but not absolutely.

It means the coronavirus is introducing variations into its sequence all the time, in this case, to bats in different habitats, different geographies, different populations. It will acquire a different consensus just by the drift of the quasispecies. We can tell where it came from. The virus that infected New York City came from Europe not directly from China—because of this quasispecies.