Are viruses the new frontier for astrobiology?
A three-dimensional representation of a norovirus virion, based on electron microscopic imagery. Should astrobiologists also be considering virions and viruses when looking for life beyond Earth? Image credit: CDC/Jessica A. Allen/Alissa Eckert.
They are the most abundant form of life on Earth, but viruses – or their seed-like dormant state, known as virions – are outliers in our search for life on other planets. Now, one group of scientists are pushing for astrobiologists to consider searching for viruses beyond Earth more seriously.
In NASA’s current astrobiology strategy, viruses are mentioned six times in its 250 pages, write the authors of a recent paper Astrovirology: Viruses at large in the Universe. They call for the study of viruses to be incorporated into extraterrestrial science missions and astrobiological research at home, and have a checklist for the actions needed to put viruses on the interplanetary map.
“Viruses are an integral part of life on Earth as we know it,” saysKen Stedman, a virologist at Portland State University’s Center for Life in Extreme Environments and a co-author on the paper. If we are going to be thinking about life on early Earth or ancient or current life on other planets, we need to be thinking about viruses, he says.
It has been more than a century since scientists discovered the first virus, and for decades it was known simply as a “very small disease-causing agent”. Late Nobel laureate Sir Peter Medawar even referred to them as “a piece of bad news wrapped up in a protein”, Stedman and colleagues write.
Their current definition is more complicated, and less defamatory: viruses are entities whose genome replicates inside living cells, and are able to transfer that viral genome to other cells. As this definition implies, viruses comprise the whole reproduction cycle – and they need other living cells to reproduce. Virions, on the other hand, are the viral seedsthat could become viruses if they happen upon compatible living cells in which to replicate. On Earth, virions and viruses go hand-in-hand with life, and if we find the former on other planets they could point to cellular life once having existed on them.
Future missions to sample the plumes of Enceladus (seen here pictured in silhouette against Saturn’s rings by the Cassini spacecraft) or Europa should carry with them experiments to detect virions and viruses. Image credit: NASA/JPL–Caltech/Space Science Institute.
On Earth, viruses are thought to outnumber cellular life forms by a factor of 10. And our planet is teeming with virions. In fact, a teaspoon of sea water can contain up to 50 million virions.
“It makes sense to be looking for the things that are likely to be the most abundant,” says Stedman, who also chairs the Virus Focus Groupwithin NASA’s Astrobiology Institute. “If an alien intelligence came to Earth looking for life, they would probably get a sample of sea water, loaded with virions. The alien life would come to the conclusion that Earth is inhabited by virions.”
“Astrovirology is no more, nor less, valid than astrobiology,” says Don Cowan, director of the Centre for Microbial Ecology and Genomics at the University of Pretoria. “There is no reason why astrovirology should not be considered with the same emphasis as ‘prokaryote’ [i.e. bacterial] astrobiology, particularly since the lesson from Earth’s biology is that every known organism has one or [sometimes many] more virus parasites.”
Part of the reason for astrovirology’s absence from space science agendas, Stedman says, is that virologists have not been reaching out to astrobiologists and pushing the case for virion hunting. Another major reason is technical: virions are tiny (with diameters ranging from 20 nanometers to over one micrometer), and so scientists need transmission electron microscopes to see their unique and varied shapes.
“While this may not be difficult on Earth, it seems unlikely that a transmission electron microscope will be put on a spacecraft in the foreseeable future,” the authors note.
Ken Stedman (right) working in his lab. Stedman is a virologist and Chair of the NASA Astrobiology Institute’s Virus Focus Group. Image credit: Joseph Thiebes.
That was one of the authors’ aims in writing their paper – to stimulate the development and testing of technologies that scientists could use in remote locations to discover virions.
“We need to look for biosignatures, and the morphologies of these virions are extremely distinctive,” says Stedman.
However, another challenge is finding a way to look for unknown virions. “We have to be careful when trying to find genomes of things that we don’t know are there,” Stedman says. While there are techniques to identify known viruses, such as high throughput sequencing or high density microarrays, identifying truly novel virions could pose a problem, the authors write.
Scientists can hunt for extraterrestrial cellular life forms, such as bacteria or more complex life, by looking for certain chemicals on a planet or in its atmosphere, but virions do not create by-products like methane or oxygen. But, the authors hypothesize, if viruses had once infected life on other planets, perhaps those viruses changed the host organism’s metabolism and this could be remotely detected from Earth. One possibility is that host organisms’ chemical by-products may be slightly different to those that had not been infected by viruses. If this was the case, this could be a proxy for detecting cellular life and viruses.
In the short term, the astrovirologists suggest that, among other things, researchers need to find distinctive virus biosignatures; consider virus-detection experiments for Europa and Enceladus; and include virus models in our models for ancient oceans and other planets.
However, Stedman says that even if there were no virions on other planets, it would be an important discovery. “If we find somewhere else where living cells don’t have viruses associated with them, [then] that would be something very different from Earth and very interesting.”
The work was supported in part by the NASA Astrobiology Institute (NAI) element of the NASA Astrobiology Program.
The Quest for Extraterrestrial Life: What About the Viruses?
Dale Warren Griffin. Astrobiology. Aug 2013Show detailsFull-text linksCite
Recently, viruses have been recognized as the most numerous entities and the primary drivers of evolution on Earth. Historically, viruses have been mostly ignored in the field of astrobiology due to the view that they are not alive in the classical sense and if encountered would not present risk due to their host-specific nature. What we currently know of viruses is that we are most likely to encounter them on other life-bearing planets; that while some are exquisitely host-specific, many viruses can utilize hundreds of different host species; that viruses are known to exist in our planet’s most extreme environments; and that while many do not survive long outside their hosts, some can survive for extended periods, especially in the cold. In our quest for extraterrestrial life, we should be looking for viruses; and while any encountered may pose no risk, the possibility of an encounter with a virus capable of accessing multiple cell types exists, and any prospective contact with such an organism should be treated accordingly.
https://www.longdom.org › t…PDFThe Role of Viruses and Viral Infections in the Theory of … – Longdom Publishing SLPanspermia proposes that life that can survive the effects of space get distributed in all habitable and non-habitable planets by meteoroids,.
“If life were to suddenly appear on a desert island we wouldn’t claim it was randomly assembled in an organic soup or created by the hand of god; we’d conclude it washed to shore or fell from the sky. The Earth too, is an island, orbiting in a sea of space, and living creatures and their DNA have been washing to shore and falling from the sky since our planets creation” –Joseph (2000).
“What has taken place on Earth represents not a random evolution, but the metamorphosis and replication of living creatures which long ago lived on other planets.” –Joseph 2000
“Our ancient ancestors, and their genes, journeyed here, from the stars.” –Joseph 1997
The discoveries and theories detailed in this text can be summarized as follows: (1) Life on Earth has extraterrestrial origins. (2) These extraterrestrials are descendants of prokaryotes and eurkayotes which had long ago “fallen” unto other planets where they engaged in interplanetary horizontal gene exchange. (3) The genetic information for the evolution of life on Earth has extraterrestrial origins, (4) Once on Earth extraterrestrial genes, including “silent genes” and the genetic material for the generation of additional genes, were transferred into the eukaryotic genome from viruses and bacteria which “fell” to Earth and (5) and their DNA contained all the genetic information necessary for the evolution of every species which has walked, crawled, swam or slithered across this planet–including species which never evolved on Earth. (6) Over the course of evolution on Earth, various species with their “libraries” of extraterrestrial genetic information, genetically and biologically altered the environment via the liberation or secretion of oxygen and calcium and other substances which (7) acted on gene selection leading to new species adapted to a world which had been genetically engineered for their survival. (8) When sufficient oxygen, calcium etc. had been secreted, and with the formation of the ozone layer, silent and other genes were activated giving rise to the Cambrian explosion (9) and the evolution of the eye, brain and skeletal system. (10) Bacteria, archae, and viruses, and perhaps even more complex species, continually fall from space and (11) continue to insert genes, via horizontal gene transfer, into the eukaryotic genome. (12) All these factors explain the step-wise, punctuated equilibrium which characterizes evolution on this planet, leading to the multi-regional evolution and metamorphosis of numerous species of human which indicates (13) Earth was genetically seeded to “grow” every species which has appeared on Earth culminating in woman and man (14) according to the genetic principles of “evolutionary metamorphosis.”
1. Overview: The Evolution of Alien Life From Other Planets
2. Origins and Evolution of Life From Space
3. Cambrian Explosion: Silent Genes, HGT, Cyanobacteria, Bones, Brains, Eukaryotic Metamorphosis, Genetic Engineering of the Environment
4. Viruses, Genetic Libraries, Evolution, Interplanetary Horizontal Gene Transfer
5. Meteors, Microbes, Viruses: Genetic Seeds of Life Keep Falling to Earth
6. Extinction, Metamorphosis, Evolutionary Apoptosis, Genetically Programmed Mass Death
7. Evolutionary Metamorphosis, Embryogenesis, and the DNA-Supra Organism
8. Multi-Regional Human Metamorphosis
9. Evolution in the Ancient Corners of the Cosmos: Even the Gods Have Gods Who Have Gods