Quorum Sensing and Viral Espionage

Shaheera Rahman
Junior
School of Life Sciences
Independent University, Bangladesh

March 23rd, 2019

Do you know how communities develop and civilizations come to be? It has taken thousands of years for human civilization to reach where it is today. This would not have been possible without communication. Communication is the vital thing that enabled us to grow as a species. However, we are not only the species that inhabits this giant planet. All other species similarly rely on communication, for survival if not for civilization as we define it. Among these other species, many are visible to the naked eye and countless others are not.

Bacteria are superstars among these unseen forms of life, at least for their sheer numbers and diversity. Could bacteria, that have existed for almost the entire span of life on earth, have been so successful without the ability to communicate among themselves? Of course not. While they do not call each other up and say, “Hey, what’s up?”, they do have their unique way of communicating and their language is known to scientists and bacterial communication enthusiasts as quorum sensing. For bacteria to use quorum sensing effectively, they need to be able to do three things: produce signals, detect the level of those signals in the environment, and produce different responses as a result of sensing the signals. If an individual bacterium picks up a lot of these signals from the environment, it immediately knows that it is in a high-density population, and starts behaving accordingly.

Quorum sensing relies on the detection of autoinducer signals at high cell densities. Small Things Considered

Now, history without war seems a bit unrealistic, doesn’t it? War has raged between us and microorganisms for millions of years but do these microorganisms not fight with each other? Of course they do. Bacteria, despite often being infectious and dangerous themselves, are at risk of getting infected themselves. By viruses! Considering the small size of viruses, one might think they are insignificant but that couldn’t be further from the truth. Viruses that infect us often cause disease, and the ones that infect bacteria, the bacteriophages, are no less devastating. Bacteriophages can cause infections in two pathways: in the first kind of infection, they activate Hulk mode and destroy everything; in more scientific terms, they infect the host cells, keep on replicating, and break apart the host cell to release all their offspring into the surroundings to infect new bacteria. In the second pathway, the virus enters stealth mode where they incorporate their genetic material into the host chromosome in such a way that every time the bacteria multiplies, the virus multiplies as well. However, in this pathway, the virus does not break apart the bacterial cell and keeps on living inside it undetected. Many bacteriophages are capable of switching between hulk mode and stealth mode.

Now, we must always remember that where there is war, there are spies as well. You know who the best spies in the world have been? Viruses! How? Allow me to explain. Certain viruses have evolved a way of tapping into the bacterial communication system in order to determine whether it would be more beneficial to use Hulk mode or stealth mode. You see, if the bacterial population is large and dense, these bacteriophages can detect this by eavesdropping on the bacterial quorum sensing system, and go into Hulk mode to infect the large pool of possible hosts. They can similarly go into stealth mode when the bacterial population is sparse as it would not be very nice to break out of a host and find no new bacteria to infect. Viruses, by definition, cannot survive for long or reproduce outside their hosts. Being tuned in to bacterial communication therefore helps these bacteriophages choose the best lifestyle for their continued survival.

Sources to explore:

Ed Yong article on a study demonstrating the phenomenon in a vibriophage
The original study

More fun research if you are interested in quorum sensing

Shaheera plans to go into biomedical research to figure out all the cures. Her hobbies include reading and eating.