Bacteria-Infecting Viruses Communicate with Each Other to Coordinate Infection

When it comes to cell invasion, viruses are pretty crafty in how they choose to infect their hosts and avoid repercussions of the immune system. After infection, however, both human viruses, such as HIV and herpes, and bacteria-infecting viruses, or phages, are usually faced with a choice: replicate quickly or lie dormant. Researchers at the Weizmann Institute of Science have found, for the first time, that bacteria-infecting viruses are more capable of making these decisions because they are able to talk to one another.

According to the press release, this communication entails “short ‘posts’ left for kin and descendants” which work to advise the viruses that encode these messages on how to best approach the infection process: replicate or remain dormant and lie in wait.

The main question was: why would a virus choose to remain dormant over replication? The researchers found that throughout the infection process, some viruses release tiny molecules into the environment , and other viruses can actually “read” the molecules at a later date. Through this means of communication, viruses are better able to “coordinate their attack” on the host.

Study author, Rotem Sorek, PhD, associate professor of the department of Molecular Genetics at Weizmann, admitted that this discovery came as even more of a surprise in that it was almost made by accident. In the press release, Dr. Sorek explained, “We were looking for communication between bacteria infected by phages, but we realized that the small molecules we were finding had been sent by the phages themselves.”

In order to prove that such an exchange was happening, the researchers first cultured bacteria and proceeded to infect those bacteria with phages. Next, they “filtered the bacteria and phages out of the culture, leaving only the smallest molecules that had been released to the medium,” according to the press release. Then the researchers went on to use the filtered mediums to grow more bacteria, which they infected with the same phages. Interestingly enough, they found that instead of killing the bacteria as they normally would, the phages become dormant.

The team then put their efforts towards isolating the “communication molecule” and pinpointing the gene that encodes it in order to understand how the molecule functions. They found that the molecule was a peptide — which they decided to name arbitrium, meaning “decision” in Latin — and that the phages would choose to become dormant when higher concentrations of arbitrium were present.

When commenting on the research, Dr. Sorek explained that the choice to replicate and kill the host at the beginning of infection makes sense for these viruses, but if they are “too gung-ho” future viruses may not have any hosts left to infect. He explained, “At some point, the viruses need to switch strategies and become dormant. The molecule we discovered enables each generation of viruses to communicate with successive generations by adding to concentrations of the arbitrium molecule. Each virus can then ‘count’ how many previous viruses have succeeded in infecting host cells and thus decide which strategy is best at any point in time.” So, how do these viruses choose to be dormant rather than replicate? The researchers found that through attachment to a “particular viral protein” that actually inhibits “the dormancy life cycle,” the peptide is able to choose dormancy.

Furthermore, the researchers found that there were a bunch of similar communication molecules in related phages. According to Dr. Sorek, “We deciphered a phage-specific communication code. It is as if each phage species broadcasts on a specific molecular ‘frequency’ that can be ‘read’ by phages of its own kind, but not by other phages.”

The team’s findings may have a number of broader implications in that, as of now, researchers aren’t certain of why viruses choose dormancy in the human body. If a similar communication strategy is being used amongst human viruses, such as HIV or herpes, then perhaps these messages can be intercepted, thus thwarting the infection process.