The topic of today's Microbial Mondays post is a question that seems simple at first, but gets at questions of life, death, and "viability". I was asked, "How do you store virus in the lab?"
To understand why this is such an interesting question, I first want to explain to you how we store the human cells that we use in the lab. We take great care in cryopreservation of human cells. We add a compound called DMSO, which is a sort of cellular anti-freeze, to cells before we store them in a -80°C freezer. DMSO basically prevents sharp ice crystals from forming during the freezing process. Without DMSO, these sharp ice crystals would form, and as they elongated, would poke lots of tiny holes in the membranes of the cells. It would kind of be like putting them through a shredder. As you can imagine, that doesn't make for happy cells.
We also add an excess of serum when freezing human cells. Serum is basically a super protein-rich and nutritious liquid that cells reeeaaaaally like. It's more important during the thawing process rather than the freezing process, for balancing out the toxic effects of the DMSO. You see, DMSO is good for preventing cell death by tiny icicles, but not so good for non-frozen cells. At concentrations of over 1%, like those that we use for cryopreservation, it kills the same cells during the thawing process, which it helps to maintain during the freezing process. So, we add the super-nutrient-rich serum to balance out that toxicity to some degree, so that we still end up with enough live human cells after we retrieve them from the freezer.
And, finally, we freeze human cells in a very controlled way. We put them in a box that cools down at a constant rate of -1°C per minute so as not to shock the poor little darlings on their way into the -80°C freezer.
Viruses, on the other hand, are easy freezers. Usually, we basically make viruses by infecting cells with virus, and then just harvesting the virus that those cells excrete. In the end, we get a virus-rich liquid. That virus-rich liquid will usually contain some serum - that nutrient-rich liquid - in it, because it's necessary to keep the virus-producing cells alive. So, we just assume that there will be enough protein in the virus-rich liquid to act as a 'good-enough' cryoprotectant… and directly stick our virus into the -80°C freezer with little ceremony.
You see, viruses are hardy little buggers. They can survive freezing even in natural, totally uncontrolled settings like lakes or permafrost, and remain "viable", or infectious, for tens of thousands of years. From a human point of view, that's pretty impressive. Sometimes I barely feel like I can survive the cold Dutch rain, let alone about 30,000 years frozen underground in Siberia.
Indeed, recently, there have been some worries surfacing about these viruses (and bacteria) that have lain dormant in the now-melting ice could indeed remain infectious and potentially cause human or animal disease. In response to these articles, a particularly fastidious report retorted, "Recently, there were news reports that a French team revived a 30.000-year-old giant virus from the permafrost in Siberia and used it to infect an amoeba. While the infection was factual, it is misleading to report this as reviving the virus, as viruses are technically not alive, in contrast to bacteria."
You see, the living nature of viruses is rather contentious. Many scientists don’t believe that viruses can ever be classified as 'alive', with their main argument being that viruses absolutely need a "host" to do most of the things that make them seem to be alive. For instance, viruses need a host to reproduce. This host can be a bacterial cell, a human cell, a dog cell... Across the wild and wonderful world of viruses, viruses collectively can invade pretty much every type of cell. But without this host, and without hijacking the host's cellular machinery, a virus cannot make more of itself.
Viruses need host cells for this one major reason: on their own, they simply don't have all the stuff they need, to do the stuff they like to do. Viruses are like hijackers: they don't own the right machinery, so they steal it from their host cell. And because a single lonely virus can't do much on its own, many biologists think it simply cannot tick the necessary boxes to be considered "alive".
However, some in the scientific community, like myself, are not convinced that this banishes viruses from the realms of the living. In terms of the reproduction argument, one lonely human cannot reproduce on its own either. We need at least a second human, or else we are left with only half the necessary goods for reproduction. On top of that, we are also hijackers of a sort. We cannot produce our own food directly like plants, so we need to hijack the nutrients from our host planet, just as a virus needs to hijack nutrients from its host cells. Just like us, once they have access to a helpful "host", viruses can self-replicate to produce little virus kids, they can evolve over generations, and they interact with and respond to their environments. To me, these collective facts make viruses seem a lot like all the other things we classify as living.
But then, if viruses are alive, they must be a different type of "alive" than us. Perhaps indeed more like the undead rather than the living. Because no human, except for maybe the International Man of Mystery, could survive being frozen for years on end, and come out the other side ready to reproduce.
So, what do you think? I think it's an open debate still. Are viruses alive? Are they undead? Or are they inanimate? Let me know in the comments!
Until next week, stay warm!
~ Alex