Viruses ‘eavesdrop’ on each other – but it can backfire

Viruses can “eavesdrop” on each other using chemical signals – but it can backfire for the eavesdropper, new research shows.

University of Exeter scientists studied chemical communication by phages (viruses that infect bacteria).

The phages assessed in this study have two choices when they enter a cell: lie dormant or kill the cell and release new virus particles to infect other cells nearby.

It was recently discovered that some phages use chemical communication systems to optimise this decision.

The new study reveals these signals do not pass solely between phages of the same species. Instead, other species – some of them barely related to the signaller – can eavesdrop.

But the signal may prompt the eavesdropper to make the wrong decision.

“The decision to kill (called lysis) or lie dormant (called lysogeny) depends on the specific situation,” said PhD student Rebecca Woodhams, from the Centre for Ecology and Conservation at Exeter’s Penryn Campus in Cornwall.

“When many bacteria are available, a phage should choose lysis and look to infect these potential hosts.

“When many hosts have already been killed and few remain, lying low and waiting for better times (lysogeny) is safer.”

The signal chemicals are called peptides, and are produced by the phage during infection. High peptide concentrations signal a lack of susceptible hosts, while low concentrations signal an abundance of uninfected hosts.

The existence of these signalling systems (called “arbitrium” systems) suggests they provide an evolutionary benefit – at least for in-species communication.

But the new study shows “cross-talk” between species does not help the “listener”.

Dr Robyn Manley, also from Exeter’s Centre for Ecology and Conservation, explained: “When a phage detects signals from another species, it is more likely to stay dormant instead of killing the cell and releasing more viruses, even when the message was not meant for it and does not reflect its own situation.

“This can benefit the virus that sent the signal, as it prevents another virus killing cells, but it can come at a cost to the virus that responds.

“In other words, viral communication is not just cooperation. Sometimes, it is manipulation.”

The bacteria and phages in the study are commonly found in soil, but the findings pave the way for further research on how viruses communicate and decide when to kill cells – with far-reaching implications for areas including human health.

This project received funding from a UK Research and Innovation grant under the UK Government’s Horizon Europe funding guarantee.

The paper, published in the journal Cell, is entitled: “Arbitrium phages can manipulate each other’s lysis-lysogeny decisions.”