We tend to think of an organism’s genetic code as monolithic and isolated, but nature is actually very leaky. Genes can move around, be duplicated, and even end up in completely different organisms. Scientists from Vanderbilt University have identified a particularly interesting example of this. A virus has been found to borrow a genes from the black widow spider, which it uses to gain access to the bacteria it infects.The virus in question is called WO, and it’s what is known as a bacteriophage. That means it infects (and kills) bacteria rather than eukaryotic cells that make up spiders, plants, humans, and all other higher life forms. WO lives in the bodies of spiders and other arthropods because that’s where you find a bacterium known as Wolbachia that WO infects. This bacteria actually lives inside the cells of its host, so WO needs a few special tricks to get close enough to strike.The researchers tested the genome of WO, and found that it contains several genes that also appear in the black widow’s genome. One of these codes for a neurotoxic protein called latrotoxin; the main active ingredient in black widow venom. This is a big gene and protein, so WO wouldn’t be carrying it around without good reason. The most likely reason, according to the researchers, is that WO can use latrotoxin to penetrate the cell membrane of eukaryotic cells, which is where it will find the Wolbachia bacteria.BacteriophagesOnce WO is in, it can infect Wolbachia and use its cellular machinery to make more copies of itself. The team has not nailed down the mechanism by which the spider’s genes found their way into a bacteriophage.Since WO doesn’t infect the spider’s cells, it can’t have picked the genes up directly. The team hypothesizes the genes could have been incorporated accidentally into phage particles during assembly, or they might have ended up in a Wolbachia bacteria to be transferred to WO when it was infected. Whatever the mechanism, it’s a really fascinating example of evolution at work.