Phages Manipulate Rivals Through Chemical Signals

Viruses known as phages, which infect bacteria, can intercept chemical messages from other phages and make decisions that sometimes harm their own interests. Scientists at the University of Exeter examined this chemical communication among phages, revealing that signals intended for one species can mislead others. These phages face a key choice upon entering a bacterial cell: remain dormant in a state called lysogeny or destroy the cell through lysis to release new virus particles for further infections.

Recent findings showed that certain phages rely on chemical signals to guide this decision. The University of Exeter study demonstrates that these signals extend beyond the same species, allowing unrelated phages to eavesdrop. However, acting on a foreign signal often leads the listener to the wrong choice. Rebecca Woodhams, co-author of the study published in Cell, noted, "The decision to kill (called lysis) or lie dormant (called lysogeny) depends on the specific situation. 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 signals consist of peptides released by phages during infection. High peptide levels indicate few susceptible hosts remain, while low levels suggest plenty of available bacteria. These systems, termed arbitrium systems, appear to offer an advantage for communication within the same species. Yet cross-species interaction disadvantages the eavesdropper. First author Robyn Manley 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 studied occur commonly in soil environments, but the findings pave the way for additional studies on viral communication and cell-killing decisions, with potential relevance to human health.