Scientists find virus with DNA stolen from the black widow

If you’re looking for nature’s version of Game of Thrones-style murder, intrigue and just a touch of ‘wait, how did this happen?’ the tale of the virus that stings like a black widow might just do it.

Wolbachia is a bacterial parasite that infects not only black widow spiders but more than half of all arthropod species, which include insects, spiders and crustaceans. In turn, Wolbachia has its own enemy in the form of a phage, a virus that attacks bacteria.

Vanderbilt biologists recently came across something of a plot twist when they discovered black widow DNA within the virus after conducting genome sequencing – a discovery that could help to fight both dengue fever and the Zika virus.

“Discovering DNA related to the black widow spider toxin gene came as a total surprise because it is the first time that a phage – a virus that infects bacteria – has been found carrying animal-like DNA,” said Associate Professor of Biological Sciences Seth Bordenstein. He and Senior Research Specialist Sarah Bordenstein reported the results of their study in  “Eukaryotic association module in phage WO genomes from Wolbachia” published the the journal Nature Communications.

Studying the Mysterious Phage

Usually phages carry specialized genes that crack the defenses of the prokaryotic bacterial cells they target. But in this case, “the portion of DNA related to the black widow spider toxin gene is intact and widespread in the phage,” said Bordenstein. “There is also evidence that the phage makes insecticidal toxins, but we are not certain yet how these are utilized and administered.”

What’s more, Wolbachia was found to have segments of DNA from other animal genomes, including those that sense pathogens and evade immune responses. “These sequences are more typical of eukaryotic viruses, not phages,” Bordenstein said.

So what’s special about this phage?

It’s thought the strange characteristic is due to the way Wolbachia wraps itself in a layer of an arthropod’s membrane after infecting it. The phage, therefore, has to force its way through these eukaryotic membranes in order to enter or escape.

“We suspect it makes pores in the membranes of the arthropod cells that surround Wolbachia, thereby allowing the phage to overcome both the bacterial and arthropod membranes that surround it. That may be how it uses some of these proteins,” Bordenstein explained.

Fighting Zika and dengue

Seth Bordenstein’s study of Wolbachia has in the past raised eyebrows, and he explains that 15 years ago, “some of my colleagues asked why I was studying such an obscure subject.” Furthermore, he and his colleagues believed that most of the work on the phage was complete and only decided to sequence its genome for the sake of completeness.

As it turned out, the effort led to much more than simply completeness.

The Bordensteins’ work helped them to identify the genetic sequences that the Wolbachia phage uses to insert its genome into the Wolbachia chromosome, and this knowledge could be used to genetically engineer the bacterium.

Wolbachia is useful in fighting dengue fever and the Zika virus because it prevents these viruses from reproducing in Aedes aegypti mosquitoes that spread them. Infecting and spreading mosquitoes with Wolbachia has been successfully field tested in Australia, Brazil, Columbia, Indonesia and Vietnam.

Use of the bacterial parasite is particularly efficient because it doesn’t rely on toxic chemicals and also because the bacteria spread rapidly through the mosquito population and sustain themselves having been introduced.

“The ability to genetically engineer Wolbachia could lead to inserting genes that cause the bacteria to produce traits that increase the effectiveness of using Wolbachia against dengue and Zika viruses. It could also be used to combat other agricultural pests,” the biologists said.

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Image credit: Thinkstock

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