Viruses may be stealthy invaders, but an Israeli study reveals a new, chatty side of some. For the first time, viruses have been “caught” communicating with one another. This communication – short “posts” left for kin and descendant viruses – helps the viruses “reading” them to decide how to proceed with the process of infection.
According to the study, during infection, viruses secrete small molecules into their environment that other viruses can pick up and “read.” In this way, they can actually coordinate their attack, turning simple messages into fairly sophisticated infection strategies.
In the future, this discovery could lead to new anti-viral treatments.
Conducted at Israel’s Weizmann Institute of Science, and recently published in the prestigious scientific journal Nature, the study reveals that many viruses face a choice after they have infected their hosts: to replicate quickly, killing the cell in the process, or to become dormant and wait.
HIV, herpes and a number of other human viruses behave this way and, in fact, even the viruses that attack bacteria – called phages, or bacteriophage – face similar decisions when invading a cell.
Interestingly, Prof. Rotem Sorek and his team at the Weizmann Institute discovered the communications between phages almost by accident. “We were looking for communication between bacteria infected by phages, but we realized that the small molecules we found had been sent by the phages themselves,” he said in a statement.
To find evidence for this communication, the team grew bacteria in culture and infected them with phages; they then filtered the bacteria and phages out of the culture, leaving only the smallest molecules that had been released to the medium. When they grew more bacteria on the filtered medium, infecting them with the same phages, they were surprised to find that the new phages became dormant rather than killing the bacteria.
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The team isolated the communication molecule, eventually discovering that it is a small piece of protein called a peptide; they also identified the gene encoding it. They found that in the presence of high concentrations of this peptide, phages choose the dormancy strategy, so they named it “arbitrium,” the Latin word for decision.
Don’t get too gung-ho
“At the beginning of infection, it makes sense for the viruses to take the fast-replication, kill-the-host route,” explains Sorek, “but if they are too gung-ho, there won’t be any hosts left for future generations of viruses to infect.”
At some point, the viruses need to switch strategies and become dormant, he says. This molecule 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.
Once they had identified this communication molecule in one phage, the researchers were able to find similar molecules in dozens of related phages – each phage encoding a slightly different communication molecule. “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,” says Sorek.
He points out that the communication-based dormancy strategy he discovered was found in phages, but it may have broader implications. “We don’t really know how viruses that infect the human body decide to go dormant. It is possible that a similar strategy to that of the phages could be used by viruses that infect us.”
If the viruses that infect humans are found to communicate with one another in a similar manner, we might learn to intercept these messages and use them to our advantage, possibly creating new kinds of anti-viral drugs.
Photos: Weizmann Institute, NIAID