A new Nature study, led by a team at MIT and the Albert Einstein College of Medicine, reminds us that the ubiquity of viruses on our own world increases by the year. To our ever-growing compendium, we can now add a new little one that hides within Earth’s oceans – “unrecognized killers of marine bacteria,” as the authors describe them.
Although they were isolated from surficial seawater, the team think that they’re more omnipresent than that, and could be found elsewhere on our pale, blue dot.
The majority of marine viruses cultured and studied in laboratories are tailed bacterial viruses, whose spiky appendage is a lethal weapon. These species use their tail to bind to receptors of the cell surface of the unfortunate bacterium. Shortly after, a biological nanomachine injects their DNA into the cell.
Here’s the thing: these new viruses don’t have tails. They aren’t the first of their kind in this sense; the authors note that “non-tailed viruses often dominate ocean samples numerically,” which suggests they are the true masters of the sea.
This discrepancy suggests we don’t know much about tailless viruses, which is why the team went to try and catch a few in the first place. They did, and they didn’t just find a new species, but an entirely new family.
They’re technically a family of double jelly roll (DJR) capsid viruses, a categorization so mellifluous it bears investigating. A capsid is just a casing that conceals the virus’ genetic material, and the DJR refers to the fact that it’s built out of proteins that are folded like a jelly or Swiss roll cake.
So far, so normal, even for a tailless virus. However, upon closer examination, the team found that the new beasties are, well, not exactly conventional.
First, instead of preying on a handful of bacteria, they seem to hunt down dozens of bacterial species, as well as members of the somewhat similar but independent kingdom, the Archaea. Unlike tailed viruses, which kill two hosts in one species on average, these new viruses “kill on average 34 hosts in four [bacterial] species.”
Secondly, their genomes are also weirdly short, containing just around 10,000 bases – far fewer than the 40,000-50,000 for tailed viruses.
It gets weirder. For such prolific killers, it seems odd that they’ve only just been spotted and sequenced.
Observing the viruses doing their thing, the team found that, despite their diversity in infectious habits and hosts, they kill the bacteria far more slowly than their compatriots. Researchers had simply been checking bacterial samples too soon, and as a result, the viruses eluded capture.
It’s only fitting, then, that their family name is Autolykiviridae, which the authors explain in their paper is “reference to Autolykos, a character in Greek mythology notable for being difficult to catch.”
This type of virus is associated with infecting animals, and very few of its kind have been seen infecting bacteria. All in all, then, this is a very novel family of viruses – and their abilities and prevalence suggest that they’re very important too, playing a major role in ecosystems.
Just recently, a team of researchers suggested that we should be looking for alien viruses out there in our Solar System. One of the key points of the said review was that viruses are particularly abundant in the oceans, which suggests that in the seas of Europe and Enceladus, entirely new ecosystems of viruses await us.
So, just as we’ve discovered this new virus hiding in our world’s coral reefs, perhaps someday, sooner rather than later, we’ll find a similar bacteria-killing critter out there in our celestial neighborhood, dominating its own extraterrestrial ecosystem.