For the first time, a virus was observed attaching to another virus. However, this never-before-seen behavior was almost missed after being discovered in a happy accident involving anomalous sequencing results.
“When I saw it, I said to myself, I can’t believe this,” Tagide deCarvalho, first author of a study announcing the discovery, said in a statement. “No one has ever seen a bacteriophage – or any other virus – attach to another virus. »
The virus in question is a bacteriophage – a virus that infects bacteria – and also a satellite virus, which relies on other “helper” viruses to complete its life cycle. Satellite viruses rely on their helpers either to build their capsids – the protein coat of a virus – or to replicate their DNA, both of which require the two viruses to be in close proximity to each other. . Now, the new study suggests that they go further, moving closer and clinging to the “neck” of their helper virus – the place where the capsid joins the virus’s tail.
But this revolutionary discovery almost did not happen. A group of undergraduate students were analyzing bacteriophage sequences from environmental samples when they discovered what they thought was contamination in the sample. The sequence of the phage they were studying was present, but so was a smaller sequence that didn’t match anything the researchers knew.
Repeating the experiment suggested that this was not an error, and electron microscopy imaging later revealed the presence of helper viruses, 80% of which had a satellite attached to their neck.
Frighteningly, some of the assistants who were not bothered by the satellite viruses still had remnants of past attachments on their necks, which lead author Ivan Erill likened to “bite marks.”
The researchers were also able to analyze the genome of the vampire viruses, as well as those of their helpers and hosts, and discovered that most satellites have a gene that allows them to integrate into the genetic material of the host cell.
However, this is not universal. In one sample, the satellite, named MiniFlayer, is the first known case of a satellite without an integration gene. He must therefore stay close to his assistant, MindFlayer, when he enters a host cell, the team hypothesizes.
“The attachment now made perfect sense,” Erill said, “because how else are you going to guarantee that you get into the cell at the same time?”
Further bioinformatics analysis suggested that this interaction between MiniFlayer and MindFlayer could be ancient, with the two co-evolving for at least 100 million years, according to Erill.
The team hopes their findings will inspire future work on this unexpected phenomenon to deepen our understanding and perhaps explain strange contamination by phage sequencing.
“It’s possible that a lot of the bacteriophages that people thought were contaminated are actually these satellite support systems,” deCarvalho added, “so now with this paper, people might be able to recognize more of them.” these systems.”
The study is published in the journal ISME.