In what may be the greatest biological weapons heist of all time, scientists have discovered a virus that steals DNA from black widow spiders in order to help it attack its victims.
The virus, known as WO, is a bacteriophage, meaning it only infects bacteria and can’t enter the eukaryotic cells of more complex organisms. Eukaryotes are cells that contain a nucleus and other membrane-bound organelles.
Though it is not uncommon for viruses to incorporate some of their host’s genes into their own DNA, it had been assumed that bacteriophages could only take DNA from bacteria, which is why the discovery of the gene for black widow venom in the WO genome is so puzzling.
Seth Bordenstein, who co-authored a paper about the discovery with his wife Sarah, told Live Science that “this is the first time, to the best of my knowledge, that animal genes were found in bacteriophages.”
WO infects a type of bacteria called Wolbachia, which lives inside the cells of black widows and many other arthropods. As such, the virus needs to be able to penetrate the membranes of these bacteria as well as the cells of the animals that host them. It also needs to avoid being detected and destroyed by the immune system of these arthropods.
Reporting their discovery in the journal Nature Communications, the Bordensteins explain that they aren’t entirely sure how the black widow genes ended up in the virus, but they suspect it helps WO to dodge the spider’s natural defenses while also increasing its deadliness to bacteria.
When sequencing the WO genome, they discovered one of the largest combination genes ever seen in a virus, which was made up of individual genes from eukaryotes and bacteria strung together. Among these was a sequence of DNA that codes for the black widow venom latrotoxin, as well as other genes that are known to trigger cell death and some that are involved in immune evasion.
Because latrotoxin works by puncturing cell membranes, the researchers suggest that this may enable WO to enter the cells of its bacterial hosts while also breaking into those of larger animals in order to access these bacteria.
Overall, this “borrowed” DNA accounts for about half of the WO genome, suggesting that this sneaky virus is a master at hijacking the weapons of others.