VIRUSES get a bad rap. Most of us only really think about them when they cause diseases, such as Ebola. They’re viewed as the quintessential hangers-on: bits of genetic material floating around that must leech off living cells to multiply and reproduce. As such, they’re often thought of as not “really” alive.

Indeed, the three of us can dimly remember from school a ridiculous mnemonic for the seven signs that supposedly distinguish life from non-life: “MRS NERG” (or “MRS GREN,” depending on your teacher).

Knowing that viruses fail on a number of those arbitrary metrics — eg R for respiration — would help you pass your biology GCSE.

Fortunately, nature is much more interesting than the school syllabus suggests.

At the molecular level, there is no clear boundary between life and non-life. Biologists (mostly) don’t worry about classifying life, they just get on with understanding it. Two such discoveries announced over the past week indicate that we’re a long way from knowing everything about viruses.

To begin with, a team of researchers based largely in California have reported finding completely new and truly massive viruses.

Some of these viruses’ genomes have more than half a million letters of DNA. For context, that’s 50 times as big as HIV’s genome of ~10,000 letters, and larger than some bacterial genomes. That alone begins to suggest that they’re capable of fairly complex things.

These viruses are harmless to humans but deadly to bacteria, and are called “bacteriophage” — literally, “bacteria devourers.” 

Although researchers have studied bacteriophages for over a century, these new varieties seem to represent a completely different strategy for survival.

Bacteriophage are the most ubiquitous viruses, found anywhere there are bacteria, but can be very difficult to study in the lab, so most are known only from their DNA.

The researchers therefore gathered samples from a vast array of worldwide locations, including hot springs in Tibet, an oil seep in Santa Barbara, and an Alaskan moose.

They then sequenced all the DNA in these samples and tried to reconstruct new virus genomes, analogous to trying to complete multiple unknown jigsaw puzzles after an explosion in a puzzle shop.

Other researchers have attempted this before, but never so successfully. Doing this carefully using new data allowed them to find over 30 new virus genomes.

Scientific terminology struggles to keep up with new discoveries like these. As no previous names existed for these new families of viruses, the researchers cheekily coined their own, including enormephage, whopperphage, and biggiephage.

Whatever you want to call them, it’s clear that these viruses are everywhere; the study also included several samples from human saliva and faeces. In other words, we’ve all been carrying trillions of these massive viruses in our mouths and guts all our lives — and we didn’t even know they were there.

The researchers also analysed the genomes to find out what the viruses were capable of.

One trick that they discovered these viruses have is particularly sneaky. Bacteria have a form of immunity which allows them to attack non-bacterial “foreign” DNA that gets into their cells.

If attacked by a virus, bacteria can incorporate small representative pieces of its genome into their own, with “red flags” around it to mark it as something to look out for.

Then, the next time the virus appears in the bacterial cell, the bacterium will recognise it as matching these small pieces, and act quickly to rip the viral genome apart.

It appears some of these massive viruses use this to their own advantage, by encoding bits of other massive viruses into their own genome with the appropriate “red flags” for the bacteria.

This means that when the virus enters a bacterial cell, the bacterium’s cellular machinery reads the viral genome and is immediately primed to attack these other viruses instead. The virus can use the bacterium’s “immune arsenal” to attack its enemies!

The way that the new massive viruses are related to each other is similar to the way the bacteria they prey on are related, indicating a long-standing evolutionary relationship that may stretch back billions of years.

The viruses might even have arisen at the same time as cells themselves.

At the opposite end of the size spectrum, a group of French researchers reported some fascinating experiments into “nanoviruses.”

They studied a tiny plant virus (a hundredth of the size of the massive viruses). Interestingly, this virus has a genome in eight separate circular chunks, making it “multipartite,” each of which encodes a different protein to reproduce the virus.

It’s been slightly mysterious how this virus manages to successfully reproduce: a plant cell would have to simultaneously have all eight chunks in it at the same time, which has a very low probability of happening (like rolling a 6 on 8 dice at once).

By designing careful experiments, the researchers found something astonishing. Using a technique that made the plant cells glow with a different colour depending on which of the eight viral proteins they were making, the mystery was solved.

Each plant cell had a distinct colour, meaning each only makes some of the viral proteins. However, on average across a whole group of cells, all the proteins get made, allowing the virus to reproduce at a population level.

It resembles a distributed manufacturing process: think Henry Ford and the automated production line for the Model T Ford. Each worker (the cell) doesn’t need to make the whole car (the virus).

They just make bits of it (different viral proteins), and then these are assembled together later (it appears the cells actually exchange viral proteins with each other allowing a whole virus to be assembled, although more research is needed).

How common this “viral Fordism” is remains to be seen, but it’s fascinating evidence that it’s at least possible, which will require rewriting some textbooks.

Whether viruses are alive or not, we take our hats off to them.

Based on the following original research papers:
Massive viruses: goo.gl/1zgFfA.
Nanoviruses: goo.gl/9FFTmv