A recent study published in Frontiers in Microbiology attracts researchers' attention because it reveals that some viruses might have the ability to monitor their surroundings and take action accordingly. To be specific, viruses can sense the environment around themselves and their host and then decide whether or when to suspend their activities, spread infection, attack or kill the host cells, multiply, and burst out inside their hosts at any given time. This finding is significant to uncover unknown interactions between viruses and their hosts and may have implications for the development of a new generation of antiviral drugs.
Bacteriophages, or simply phages, are viruses that infect and harm bacteria. In this study, researchers look into a phage that can only infect the host when the bacterial cells have special appendages—pili and flagella that can help the bacteria move and mate. Specifically, this flagellotropic phage infects Caulobacter bacteria cells, which have two forms. One is the non-motile stalkers when the food is plentiful, and the other is removable swarmers with flagella/pili when the food is scarce.
Researchers conducted further analysis on this flagellotropic phage and discovered binding sites for a protein called CtrA in the DNA of this phage. The interesting fact is that a phage would never produce the CtrA protein. Conversely, the CtrA protein is usually produced by the bacteria to control the generation of appendages that enable the microorganism to move, attach, reproduce, and infect a host. In other words, it's the CtrA protein that decides whether the bacterial cell would divide to form stalkers or swarmers.
In the process of understanding why the phage's DNA has a binding site for CtrA and how it distinguishes different forms of caulobacterales to infect, researchers noticed that the binding sites to CtrA could be found in many different types of phages and all of them can only infect hosts with pili/flagella, the so-called swarmer cells.
Consequently, researchers suggested that these flagellotropic phages might have the ability to monitor the level of the CtrA protein in a caulobacter cell, which is a signal for the phage to kill the bacteria when a factory of swarmers is produced. What's more, the ability could be developed several times by diverse phages that infect different bacteria until distantly related species exhibit a similar trait through convergent evolution.
In addition, taking advantage of the CtrA binding sites to recognize bacteria with pili/flagella and monitor their environment before any actions is believed just one of the many talents of bacteriophages. For instance, researchers in this study also make a bold prediction that certain phages might have receptors that allow them to listen in on the activities taking place inside their host cells and they think the viruses that affect humans are bound to have the same ability.
The significance of this study is that as more information about such binding sites and receptors is discovered, more and better phage-based therapy or antiviral drugs could be developed. That's to say, if scientists know viruses in humans are listening in on a particular signal to detect the tissue types surrounding them or immune responses to their infection, which help them optimize survival and replication strategy, then researchers probably can develop antiviral drugs that trigger fake signals to fool viruses.
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