Black widow spider genes found in virus

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A black widow spider spinning a web. These creatures can be infected by bacteria which, in turn, are infected by viruses.
Credit: Mark Kostich / Getty Images

A virus that only infects bacteria has been found sharing genes with animals, including the black widow spider, according to a new study.

A pair of US researchers sequenced the genome of the bacteria-infecting virus WO and found a section of its genome comprised animal-like genes. This is bizarre, because even though viruses do swap bits of DNA with their hosts, they were thought to only do so exclusively with the domain they infect – such as bacteria – not others.

They published their findings in Nature Communications.

Viruses keep to their own domains. There are those that infect bacteria (bacterial), those that infect single-celled organisms (archaeal) and those that infect animals and plants (eukaryotic).

For instance, a bacterial virus might nab DNA from its host bacteria, perhaps to help them combat its immune response, but they generally won’t cross over into the other two domains.

But Sarah Bordenstein and Seth Bordenstein at Vanderbilt University in Nashville, US, found evidence that perhaps that’s not entirely the case.

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Wolbachia infected with tiny virus particles.
Credit: Michelle Marshall and Seth Bordenstein

They focused on Wolbachia – a genus of bacteria that infect 60% of the world’s insects.

This makes it one of the world’s most common parasites, although it can sometimes offer a mutually beneficial relationship with its insect host.

But Wolbachia itself is also susceptible to infection – by a bacterial virus known as WO.

For their study, the pair of researchers conducted a detailed genome sequencing of WO using particles lifted from moths and wasps infected with Wolbachia.

They uncovered a section of the WO genome that closely resembled the genes of insects and spiders.

The most prevalent animal-like gene coded for the protein latrotoxin-CTD, which is central to the venom function of the black widow spider (Latrodectus sp.).

They also found genes that mediate transport across cell membranes. This could help the virus infiltrate the cells of animals in an effort to reach and infect their bacterial targets.

The researchers say the genes probably originated in animals, and were subsequently incorporated by the virus, although the process of transfer is not yet understood.

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