Virus steals black widow poison gene to help it attack

By Bob Holmes

Robbed by a bacterium. Photo by Robert Llewellyn/Getty
Robbed by a bacterium. Photo by Robert Llewellyn/Getty
Genetic Theft

In one of the most unexpected genetic thefts ever, a virus that infects bacteria appears to have stolen the gene coding for the poison of the black widow spiders. The virus, named WO, probably uses the gene to help it attack its targets.

Viruses often steal genes from their hosts. But because bacterial viruses – also called bacteriophages – only attack bacteria, genes from other domains of life are usually beyond their reach. That would include higher organisms known as eukaryotes, which have cells that contain a nucleus.

Wolbachia infected by viruses, enlarged in the inset (bottom left) Wolbachia infected by viruses, enlarged in the inset (bottom left)Michelle Marshall and Seth Bordenstein

Wolbachia infected by viruses, enlarged in the inset (bottom left) Michelle Marshall and Seth Bordenstein
Immune Evasion

WO, however, faces an unusual challenge: its targets are Wolbachia bacteria living within the cells of insects, spiders, and some other animals. That means that for it to infect new bacterial cells, WO has to escape not only from its existing Wolbachia host, but also from the eukaryotic cell – and then the virus particles have to evade the eukaryote’s powerful immune system.

Many viruses of eukaryotic cells co-opt genes from their hosts to help them do this. To see if WO could do the same, Sarah and Seth Bordenstein, microbiologists at Vanderbilt University in Nashville, Tennessee, sequenced its genome and studied the provenance of its genes.

They found several genes closely related to ones found in eukaryotes, including the gene for latrotoxin, the poison used by black widow spiders. It kills by poking holes in cell membranes, making it a plausible tool for a virus needing to escape from a eukaryotic cell.

WO also had other genes like those in eukaryotes, and these may help it evade the immune system.

Eukaryotic Genes in a Bacterial Virus

This is the first time eukaryotic genes have turned up in a bacterial virus. What’s more, the eukaryote genes make up almost half of WO’s genome.

“For a phage to devote about half its genome to these eukaryotic-like genes, they must be important to the phage function,” says Sarah Bordenstein. WO probably picks up the eukaryote DNA after breaking out of a Wolbachia cell into the animal cell.

This unusual gene theft shows the evolutionary adaptability of phage viruses, says Ry Young, director of the Center for Phage Technology at Texas A&M University, College Station.

Their high mutation rate, rapid life cycle and vast numbers mean that almost any conceivable adaptation is likely to occur relatively quickly.

“Phages are the most advanced form of life on Earth,”

he says, only partly in jest. “They’ve evolved more than we have.”

This article was first published at NewScience.

_______________________________________________

For a more in-depth review of these findings see: Eukaryotic association module in phage WO genomes from Wolbachia by Srah bordenstein and Seth Bordenstein  published in Nature Communications.