WO is a virus that lives in bacteria called Wolbachia, which in turn is found in the cells of many insects. Husband-and-wife microbiologists Seth and Sarah Bordenstein, specialists on WO, have been studying the virus for over a decade when they found something extremely unusual in its DNA sequence—a third of WO's genes came from an unfortunate black widow spider.
WO, like all viruses, works by inserting itself in its host's genome, and as the host reproduces, makes copies of WO along with it. It's a bacteriophage, and its mission is to replicate itself within bacteria like the Wolbachia until it bursts. When WO is out in the open, it somehow works itself back through the insect's cells, and through the bacteria's. It's a mechanism that hasn't been explained before—but as the Bordensteins discovered the unusual cluster of animal DNA in WO, the working theory is that the virus infected the spider.
This would usually be deemed unlikely, as viruses stick to their established biological boundary—in this case, just the WO should have infected Wolbachia only. “It’s the first report of a virus infecting multiple domains of life,” comments Wolbachia specialist Elizabeth McGraw. She suspects that WO had become “a Frankenphage that may be better at infecting animals than its ancestors that contained only phage genes.”
The Bordensteins theorize that WO "took" the arachnid's genes to help it become better at piercing through insects and Wolbachia cells and to toughen it against several boundaries of defense. Their work can be accessed through Nature Communications.
There's still so much we don't know about our world and the creatures that inhabit it. The mechanism exhibited by the virus points to distressing clues about how viral diseases can adapt to toughen themselves against treatment. For the meantime, we're all watching out for the next discovery.