Viruses can transfer genes to organisms they are not known to infect, including organisms in different domains (superkingdoms) of life, according to a study published in the journal Frontiers in Microbiology.
Malik et al find that viruses and cellular organisms share a large group of genes that help cells to function, suggesting that viruses may have an ancient cell-like origin. Image credit: John Voo / CC BY 2.0.
Viruses can sometimes infect very different organisms during their lifecycle, such as mosquitoes and humans in the case of Zika virus. They can also jump between different species, such as from birds to humans.
However, no virus has been discovered that can infect organisms from different superkingdoms.
“Normally, we associate viruses with very specific host organisms, and we do not know of any virus that, for example, can infect both bacteria and humans,” said co-author Dr. Arshan Nasir, from the University of Illinois and COMSATS Institute of Information Technology, Pakistan.
“Virus-host boundaries make sense since organisms that are separated by large evolutionary distances differ starkly in their cellular biology. This makes it hard for a virus to successfully replicate inside two very diverse environments.”
Nevertheless, Dr. Nasir and co-authors suspected leaps between such distant species could occur, not necessarily involving virus infection.
“In addition to infecting and killing cells, viruses can also insert their genes into a cell’s DNA. We therefore hypothesized that viruses might interact in non-harmful ways to exchange genes between distantly related organisms,” Dr. Nasir said.
To investigate such viral gene exchange, the team looked at protein structures found in all known viruses and cellular organisms.
By looking for protein structures that are specifically associated with viruses or cells, the scientists could detect virus-derived genes in cellular organisms and cell-derived genes in viruses.
Strikingly, viral hallmark genes weren’t just found in the expected host organisms, but in all sorts of species — including those from different superkingdoms.
“For example, we found examples where viruses thought to only infect bacteria had likely transferred genes to complex organisms, such as plants and animals,” they said.
“This suggests that viruses can transfer genes to organisms that are dramatically different from their usual host, and that they can influence and interact with a much wider range of organisms than previously thought.”
The study’s authors also found evidence that viruses and cellular organisms share a large group of protein structures that help cells to function.
“This is a little surprising in the case of viruses, as they aren’t cells and have no obvious need for these proteins,” the researchers said.
“One intriguing possibility is that viruses may have originally evolved from primitive cells, and these proteins were once useful during their ancient origins.”
“We believe the results could change the way we think about virus-host relationships,” Dr. Nasir said.
“The study shows that the concept of a ‘virus host’ is rather blurry, since viruses do not necessarily need to kill a cell in order to interact with it.”
“We should consider viruses to be a source of new genes that cellular organisms can acquire, and not necessarily just as a source of disease.”
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Shahana S. Malik et al. Do Viruses Exchange Genes across Superkingdoms of Life? Front. Microbiol, published online October 31, 2017; doi: 10.3389/fmicb.2017.02110
