Phages can sense DNA damage in bacteria, which triggers replication and jumpship.
A virus may be “watching” you. Some microbes wait until the host unknowingly signals them to start multiplying and kill.
especially after more than two years[{” attribute=””>COVID-19 pandemic, many people picture a virus as a nasty spiked ball – essentially a mindless killer that gets into a cell and hijacks its machinery to create a gazillion copies of itself before bursting out. For many viruses, including the coronavirus that causes COVID-19, the “mindless killer” moniker is essentially true.
However, there’s more to virus biology than meets the eye.
A suitable illustration is HIV, the virus that causes AIDS. HIV is a retrovirus that does not immediately go on a killing spree when it enters a cell. Instead, it integrates itself into your chromosomes and chills, waiting for the proper opportunity to command the cell to make copies of it and burst out to infect other immune cells and eventually cause AIDS.
Bacteriophages, or simply phages, are naturally occurring viruses that attack and kill bacteria. They cannot infect human cells. Phages are extremely diverse and exist everywhere in the environment, including in our bodies. In fact, humans contain more phages than human cells.
A phage has three main parts: a head, a sheath, and a tail. The phage uses its tail to attach to a bacterial cell. They use the bacteria to replicate themselves. After finding a “matching” bacterial cell, the phage injects its genetic material, hijacking the system normally used for bacterial reproduction. Instead the system will make thousands more phages, which ultimately burst the bacterial cell, releasing it into the environment.
Exactly what moment HIV is waiting for is not clear, as it’s still an area of active study. However, research on other viruses has long indicated that these pathogens can be quite “thoughtful” about killing. Of course, viruses cannot think the way you and I do. But, as it turns out, evolution has bestowed them with some pretty elaborate decision-making mechanisms. For example, some viruses will choose to leave the cell they have been residing in if they detect DNA damage. Not even viruses, it appears, like to stay on a sinking ship.
For over two decades, my laboratory has been studying the molecular biology of bacteriophages, or phages for short, the viruses that infect bacteria. Recently, my colleagues and I demonstrated that phages can listen for key cellular signals to help them in their decision-making. Even worse, they can use the cell’s own “ears” to do the listening for them.
Escaping DNA damage
If the enemy of your enemy is your friend, phages are certainly your friends. Phages control bacterial populations in nature, and clinicians are increasingly using them to treat bacterial infections that do not respond to antibiotics.
The best-studied phage, lambda, works a bit like HIV. Upon entering the bacterial cell, lambda decides whether to replicate and kill the cell outright, like most viruses do, or to integrate itself into the cell’s chromosome, as HIV does. If the latter, lambda harmlessly replicates with its host each time the bacteria divides.
This video shows lambda phage infecting E. coli.
However, like HIV, Lambda isn’t just left alone. Like a stethoscope, he uses a special protein called CI to listen for signs of DNA damage within bacterial cells. When the bacterial DNA is compromised, it’s bad news for the lambda phage nested inside. Damaged DNA goes straight to the evolutionary landfill because it’s useless for the phages that need to reproduce. So lambda turns on its replication gene, makes copies of itself, and flies out of the cell to seek out other undamaged cells to infect.
eavesdrop on a cell’s communication system
Instead of gathering information with their own proteins, some phages utilize the infected cell’s very own DNA damage sensor, LexA.
Proteins such as CI and LexA are transcription factor It turns genes on and off by binding to specific gene patterns within the instructions of DNA, the chromosome. We found that some phages, such as Coliphage 186, do not require their own viral CI protein if they carry a short DNA sequence on their chromosome that allows bacterial LexA to bind. Upon detecting DNA damage, LexA activates the phage’s replicate-and-kill gene, essentially causing the cell to double-cross and commit suicide, allowing the phage to escape.
Researchers first report the role of CI in phage decision-making in the 1980s and Coliphage 186 counterintelligence tricks late 1990sSince then, there have been several other reports of phages eavesdropping on bacterial communication systems.An example is Phage phi29It utilizes host transcription factors to detect when bacteria are ready to produce spores or a type of bacterial egg. Able to withstand extreme environmentsPhi29 instructs the cell to package its DNA into spores and kills the budding bacteria when the spores germinate.
https://www.youtube.com/watch?v=MkUgkDLp2iE
Transcription factors turn genes on and off.
of recently published research, my colleagues and I show that several groups of phages have independently evolved the ability to utilize yet another bacterial communication system, the CtrA protein. It integrates external signals to initiate various developmental processes in bacteria. Key among these is the production of bacterial appendages. flagella and fimbriaeAfter all, these phage attach to and infect the fimbriae and flagella of bacteria.
Our main hypothesis is that phages use CtrA to infer when there are enough bacteria near the sporting fimbriae and flagella to readily infect them. Quite a clever trick for a “heartless killer”.
These aren’t the only phages that make sophisticated decisions – they all don’t even have the advantage of having brains. bacillus Bacteria produce small molecules every time they infect a cell. Phages sense this molecule and Count the number of phage infections happening around them. As with alien invaders, this count helps determine when to turn on genes that replicate and kill only when the host is relatively abundant. It ensures its own long-term survival by ensuring that it never runs out of hosts.
counter virus counterintelligence
A good question is why we should pay attention to counterintelligence operations carried out by bacterial viruses.Bacteria are very different from humans, but the viruses that infect bacteria are not much different from viruses that infect humans.rather every trick It was later shown to be played by phages and used by viruses that infect humans. If phages can eavesdrop on bacterial lines of communication, why can’t human viruses eavesdrop on yours?
So far, scientists don’t know what they’re hearing if a human virus hijacks these lines, but there are many possible options. I believe it may be possible to count and strategize, detect cell growth and tissue formation, and even monitor immune responses. However, scientific research is ongoing.
Having a virus overhear a cell’s private conversations is far from optimistic, but it’s not without its silver lining. As intelligence agencies around the world know very well, counterintelligence only works undercover. Once detected, the system can be very easily exploited and misinformed the adversary. Similarly, future antiviral therapies will combine traditional artillery, such as antiviral drugs that prevent the virus from replicating, and information warfare ploys, such as tricking the virus into believing that the cell it is in belongs to another tissue. I believe it might be possible to combine them.
But shut up and don’t tell anyone. A virus may be listening.
Written by Ivan Erill, Associate Professor of Biological Sciences, University of Maryland, Baltimore County.
This article was originally published conversation.
