The language of viruses

Feb ,14 2017

A team of scientists from Weizmann Institute of Science in Rehovot, Israel, discovered a mechanism by which viruses, more specifically bacteriophages that infect bacteria Bacillus, can communicate. This is the first time ever that any form of viral communication was described, and results of this research were published in journal Nature.

That bacteria can communicate using secretion and detection of chemical messengers was already described and this phenomenon is called quorum sensing. Through quorum sensing, bacteria can adjust their behavior according to the numbers of other bacteria around. The team lead by microbial geneticist Rotem Sorek was initially looking for evidence that a bacterium Bacillus subtilis is able to alert other bacteria in their population to phages. To their surprise, the team discovered something genuinely extraordinary: phages are the ones that communicate in order to “decide” the faith of their victims. Some phages can infect bacterial cells in two distinct ways, using lytic or lysogenic cycle. Usually they hijack host bacterial cells and multiply until the host bursts and dies (lytic cycle). However, sometimes, phages integrate their own genetic material (genome) into the host’s genome. Like this, they can stay dormant for a longer period of time, until a trigger “wakes them up” and they start multiplying. The decision whether to enter lytic or lysogenic cycle was believed to be random, but as the team around Sorek shows, a phage called phi3T makes a chemical that can change behavior of their viruses and influence decision making. They filtered the contents of the flask to remove bacteria and viruses, in order to keep the small molecules, and when they added this medium to a fresh culture of bacteria and phages, the behavior of phages changed, and they were rather undergoing lysogenic cycle than killing bacteria. The new molecule was named arbitrium and later identified as a short viral protein that goes out of infected bacteria once they are killed. When levels of arbitrium rise above a certain threshold – meaning a large number of bacteria have died, phages stop killing and “choose” to rather integrate their genome in bacterial genetic material. This viral chemical communication system serves to ensure that there are always some host cells left alive, so that viral particles can further multiply. Sorek’s team additionally identified other systems of phage communication, which are independent of each other, meaning that they all “speak” different languages.

Now there are reasons to assume that viruses that infect humans, such as HIV or herpes, could utilize similar communication systems. If the “messenger” molecules with functions similar to arbitium would be identified, than we could potentially target those molecules and influence the behavior of the virus.