A team of researchers has announced the discovery of a new group of viruses in the oceans. Hitherto elusive, they play a major role in bacterial regulation.
The ocean is crowded: no less than 10 million viruses can be in a single milliliter of water. While most are known, others on the other hand remain out of sight. At least until now. A team of microbiologists announced the discovery of a family of viruses previously unknown that dominates the ocean and can not be detected by standard laboratory tests. The researchers suspect that this viral family could also exist out of the ocean, and perhaps even inside our body.
“We do not think it’s ocean-specific,” says environmental microbiologist Martin Polz of the Massachusetts Institute of Technology (MIT).
The researchers analyzed three months of water samples taken from the ocean off the coast of Massachusetts. They then succeeded in isolating and studying specimens of these viruses, which are a missing link in the evolution of viruses, and play an important role in the regulation of bacterial populations. What they found floating in the water is also remarkable by the fact that these viruses do not look like any other.
According to the researchers, the most abundant viruses worldwide are double-stranded DNA viruses (dsDNA), of which the “tail” variety (Caudovirales) is the best known. The tailless specimens discussed here are much less well known, mainly because their biological characteristics are not easily detectable by common tests. But it is now done, since researchers have been able to sequence their DNA. They also named this new group “Autolykiviridae” – after Autolycos, a character from Greek mythology known to be difficult to catch.
These tailed viruses appear to be representatives of an older viral lineage defined by specific types of capsid – the proteinaceous shell that surrounds viral DNA. The latter commonly infect animals and unicellular organisms, but not bacteria.
The genomes of this new family are very short compared to the tail viruses, because they consist of about 10,000 bases, instead of 40,000 to 50,000 in general for the tail viruses. Moreover, while most viruses only attack one or two types of bacteria, they seem to be able to infect dozens different, suggesting that they play a disproportionate role in terms of regulation of bacterial life in the ocean.
This ruthless efficiency might not be limited to the ocean, as this new group of viruses seems indeed to be particularly widespread. The researchers suggest that we could actually find them in the human microbiome. Indeed, by sifting through the DNA databases to see if scientists had ever studied similar viruses, the stomach appeared in the results. Further research will be needed to understand the implications of these viruses – whether in the ocean or in other ecosystems.