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Black Widow Spider DNA Uncovered in Bacteriophage Genome

NEW YORK (GenomeWeb) – The bacteriophage WO, which infects the bacterial parasite Wolbachia, harbors genes that are eukaryotic in origin, including one that appears to be from a black widow spider, two Vanderbilt University researchers have reported.

The WO phage infects Wolbachia, bacteria that themselves infect a number of arthropod species including spiders and crustaceans. As they reported in Nature Communications this week, Vanderbilt's Seth and Sarah Bordenstein conducted a metagenomic analysis of WO particles isolated from Wolbachia, and uncovered a set of eukaryotic genes that included the black widow latrotoxin C-terminal domain.

"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," Seth Bordenstein said in a statement.

The Bordensteins isolated WO particles from Nasonia giraulti wasps and Ephestia kuehniella moths that were infected with different strains of Wolbachia. Through sequencing, they found that these WO isolates contained known phage genetic modules like head, virulence, and tail modules, among others. But they also noticed a new group of genes that were more typical of eukaryotes.

They dubbed this group of genes the 'eukaryotic association module (EAM)' and confirmed its presence in an independent sample of WO-infected Wolbachia.

The researchers analyzed the homology and architecture of the EAM genes to find that they harbored both eukaryotic-like and bacterial protein domains. In particular, they uncovered 10 protein domain types with putative eukaryotic functions, including involvement in toxins, host-microbe interaction, host cell suicide, and the secretion of proteins through the cell membrane.

The most prevalent eukaryotic-like domain in the WO phage genome is latrotoxin-CTD, the researchers reported. Latrotoxin is a key component of black widow spider venom and helps punch ion-permeable membrane pores in spider-bite victims. CTD, they noted, is associated with the latrotoxin precursor molecule.

Based on their phylogenetic analysis, the researchers reported that this toxin appears to have come to WO phages from black widow spiders themselves.

"The portion of DNA related to the black widow spider toxin gene is intact and widespread in the phage," Bordenstein added. "There is also evidence that the phage makes insecticidal toxins, but we are not certain yet how these are utilized and administered."

The Bordensteins similarly reported that the programmed cell death gene NACHT also appears to have undergone horizontal genetic transfer into WO phage. Their phylogenetic analysis traces its origins to the silk moth, Bombyx mori, or perhaps the southern house mosquito, Culex quiquefasciatus.

But how these genes have been transferred from animals to viruses isn't yet clear, the researchers said. Genetic material could move directly from the host animal to the phage, it could move from the animal host to Wolbachia to the phage, or it could move through another intermediary.