The story so far…
Without viruses, the planet as we know it would cease to exist
Now, now, now !! Let me take a break. We all know how a virus, something between living and non-living can destroy us! Our lives and our families. Our society and our economy! The proof is before us! And here, I am just going on saying that viruses are ‘needful’! Even some can be ‘good’! Even giving examples !!
Does this mean that all I have talked about till now is just a joke in front of all the damage a virus can cause?
Check the next part of this to find it out!
READ PART 1 HERE.
~ Part 2 ~
What we have discussed so far is nothing, but, just our negligence regarding these particular domains of ‘acellular life’. Most people are unaware of the role viruses play in supporting life on Earth, because we only tend to concentrate on the ones that cause havoc. Surprisingly, almost all virologists solely study pathogens; only recently have a few intrepid researchers begun studying the viruses that keep the planet alive. Perhaps, the recent upsurge in viral infections like Ebola, Zica and encephalitis are the main root causes of such sudden, recent and limited interest.
According to many virologists, if we try to construct a wooden house, but, decide to pull away all the nails out of it, the result would be very similar to what our earth would be without the viruses. Strange it seems!
To appreciate the multifariousness of viruses, we need to start with the basics of what they are and what they are not. We know, what it is not. It is not a living cell. Cannot replicate on its own. We all are made of cells. Those add up to form the complexities. Bacterium and other microbes are much similar; but smaller. But viruses? They are miles apart!
A molecular picture of viruses
We have tried to explain it in many ways since ancient days. Sometimes we speculated that it was just an infectious liquid. For a time, a virus was defined as something that was much smaller than a bacterium but could cause diseases. Later, a virus was considered a submicroscopic agent, having only a very small genome, that could replicate inside living cells—but that was just a first step toward a better understanding.
Perhaps, it easier to describe virsues than to define them. Each viral particle has a stretch of genetic instructions (DNA or RNA) packaged inside a capsid which is a protein capsule. The capsid is sometimes surrounded by a membranous envelope (like the caramel on a caramel apple), that not only defends it but also helps it catch hold of a cell. A virus can replicate only by entering a cell and commandeering the 3D printing machinery that converts genetic information into proteins.
If the host cell is out of luck, many new viral particles are made which come busting out wrecking the cell in the process. That kind of damage—like what the SARS-CoV-2 causes in the epithelial cells of the human airway—is partially how a virus tunrs into a pathogen. But, if the host cell is lucky, the virus can simply settle into this cosy outpost—either going dormant or reverse-engineering its little genome into the host’s genome—and bides its time. This second possibility carries many implications for the mixing of genomes, evolution, and even our sense of identity as humans.
Interesting! Now. Do we have all viruses of the same capabilities? How many viruses are there? How many are documented? We already discussed the number is beyond count !! But, what are the varieties?
Counting the viruses!
For a start, researchers have no idea as to how many viruses even exist. Thousands have been formally classified, but millions remain undiscovered. Since we were not interested in it, we never gave a serious look into them. And then, they multiplied, mutated, and evolved. Even scientists do not know what percentage of total viruses are problematic toward humans. It is apprehended that If you looked numerically, it would be statistically close to zero. Most viruses out there are not harmful to things we care about.
But, we know something very important about them. It is well-known fact that phages, or the viruses that infect bacteria, are extremely important as the major predators of the bacterial world. Life would be difficult without them.
But, exactly why? Let us explore that.
Viruses – guardian of the natural world?
Phages are the primary controller of bacterial populations in the ocean, and probably in every other ecosystem that we know of. If viruses suddenly vanished, some bacterial populations would likely explode; and the others might stop growing completely due to competition. This would especially cause problems in the oceans, where majority of life is microbial in nature. Those microbes are able to produce about half the oxygen on the planet and this process is sort of enabled by viruses. These viruses eliminate about 20% of all oceanic microbes, and arouond half of all oceanic bacteria, each day. By this, viruses ensure that oxygen-producing plankton has enough nutrients to undertake sufficient amount of photosynthesis, ultimately helping to sustain much of life on the planet. If we don’t have death, then we can have no life, since life is totally dependent on the recycling of materials. Actually, we find the viruses here, in this particular domain, are enacting an important role in terms of recycling.
Biologists dealing with pests in agricultural sciences have notified the action of viruses is essential for species population control. If a particular species becomes overpopulated a virus will come through and wipe them out. A good saying is “Wipe the Winner.” It’s a very natural part of ecosystems and is common in many other species. Just a game of checks and balance. And, it follows the logical growth curve as well, with a definite carrying capacity, under given resources, at a given place at a given time. When populations become very excessively high, viruses tend to replicate very rapidly and bring that population down, creating space for everything else to survive. If viruses cease to exist all of a sudden, competitive species likely would flourish which would be detrimental to others
Aren’t we suffering the same problem during this pandemic period?
The human population is ever increasing. Our resources are crunching down as days pass on. We ourselves don’t know the carrying capacity of the earth for ourselves. So, has the virus come to remind us of our limits?
Looks like they are the guards of the natural world !!
But, what about us?
Likewise, researchers think that viruses are integral for maintaining healthy microbiomes in the bodies of humans and other animals. Though these things are not well understood, we’re encountering more and more instances of this interaction of viruses being an important part of ecosystems, whether it’s our human ecosystem or the environment, discovered concrete evidence supporting this. In one study, it has been examined a fungus that colonises a specific grass in Yellowstone National Park is infected by a virus which allows the grass to become tolerant to geothermal soil temperatures. When all three are present – the virus, fungi and plant – then the plants can thrive in really hot soils. It is not possible for the fungus to do it alone.
Infection with certain benign viruses even can help to ward off some pathogens among humans.
GB virus C, a common blood-borne human virus, is a non-pathogenic far-flung relative of West Nile virus and dengue fever, is associated with delayed progression to Aids in HIV-positive people. It has also been found that GB virus C may make people infected with Ebola less likely to die.
Really?! Do virus-infected people have fewer chances of death?
Seems quite hard to believe after the CoViD impact, right?
Viruses in therapy – phage therapy
Viruses are also some of the most encouraging therapeutic agents for treating certain diseases. Phage therapy,for instance, uses viruses to target bacterial infections. This was the subject of considerable research in the Soviet Union as far back as the 1920s! Today, this field is growing really fast – not only because of the menace of antibiotic resistance but also because this allows us to fine-tune treatments to knock out specific bacterial species rather than indiscriminately wipe out entire bacterial populations like antibiotics. Oncolytic viruses are ones that selectively infect and destroy cancer cells. They are also increasingly being researched upon as a less toxic and more efficient way to treat cancer. Whether targeting harmful bacteria or cancer cells, therapeutic viruses act like little guided missiles that go in and blow up the cells are just not required and can be very harmful. We need viruses for research and technology development efforts that are going to lead us into the next generation of therapeutics.
At the School of Medicine of Stanford University , Joanna Wysocka and her colleagues have found evidence that viral fragments produced by the human endogenous retrovirus, known as HERV-K, might help in protecting the embryo from viral infection, or in controlling development of the foetus, or both. These viruses are present within human embryos at the earliest stage of development. However, this aspect needs more in-depth knowledge and hence, more research. Further, her group has focused on a specific transposon that has possibly entered the human genome as a prologue section of HERV-K. It has then found ways of copying itself and bouncing to other parts of the genome, such that it’s now present in 697 scattered copies which probably help turn on almost 300 human genes.
The HERVs are about 8% of the human genome. If 8% of each of our genome is retroviral DNA, and half is transposons, then probably the very notion of human dsitinctiveness (or human supremacy for that matter) is not as solid as we think!
A very striking example in this regard would be of the mammalian placenta and the timing of gene expression in human pregnancy. Evidence suggests that we our ability to have live births is to some extent related to a bit of the genetic code that was co-opted from ancient retroviruses that infected our ancestors millions of years ago. It is intriguing to contemplate that human pregnancy would be very different (or even non-existent!) were it not for aeons of retroviral pandemics troubling our evolutionary ancestors.
So what can we conclude about viruses?
We find that the viruses take and viruses give. Now that we have somewhat idea about how viruses are beneficial for us, I will now give an insight into the other side of the game.
Charles Darwin, the father of evolution, taught us the arboreal analogy of depicting and explaining evolution. But, that does not go hand in hand with the horizontal gene transfer mechanism. Even viruses, which may seem so basic at first look, are very complicated. Their complexity gives us humans a clearer idea about the tangled connectedness of the natural world. Scientists have only recently begun to identify the various ways that viruses help to make our lives easier or better because they have only just begun to look. Ultimately, though, the more we learn about all viruses, the better equipped we will be to harness certain viruses for good and to develop defences against others that could lead to the next pandemic.
It is now up to you to decide, whether, viruses are good or bad.
Whatever be your judgement, you certainly cannot undermine the immense potential of these invisible particles in our lives – whether unveiled yet or not.
Swarnendu Saha (2nd-year BS-MS student, Indian Institute of Science Education and Research Kolkata).
- Roossinck, M. J. (2015). Move Over, Bacteria! Viruses Make Their Mark as Mutualistic Microbial Symbionts. Journal of Virology, 89(13), 6532–6535. doi:10.1128/jvi.02974-14
- American Society for Microbiology. “Viruses: You’ve heard the bad; here’s the good.” ScienceDaily. ScienceDaily, 30 April 2015.
- How ‘good’ viruses may influence health
- Mietzsch, M., & Agbandje-McKenna, M. (2017). The Good That Viruses Do. Annual Review of Virology, 4(1), iii–v. doi:10.1146/annurev-vi-04-071217-100011
- Farah, T. Sometimes, Viruses Can Be Good For Your Health. Jun 23, 2020 3:20 AM, Discover.
- Wei-Haas, M. Viruses, explained. Feb 23, 2019, Science – Reference, Nat. Geo.
- Wu, K.J. There are more viruses than stars in the universe. Why do only some infect us? Apr 15, 2020, Science – Coronavirus Coverage, Nat. Geo.
- Varshney, V. International Day for Biological Diversity 2020: Why viruses are necessary. May 22, 2020, Science and Technology, DownToEarth.
- Lodish H, Berk A, Zipursky SL, et al. Molecular Cell Biology. 4th edition. New York: W. H. Freeman; 2000. Section 6.3, Viruses: Structure, Function, and Uses. Available from: https://www.ncbi.nlm.nih.gov/books/NBK21523/
About the author:
A student of 3rd-semester IISER KOLKATA, I, Swarnendu Saha is a pass-out of South Point High School and is a travel enthusiast, who loves to travel anywhere, below the sky. Rather than saying which subject I like, let me say, I do not like Chemistry at all.