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Do Viruses Lie Low?

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Viruses
Courtesy of Michael Kwok (Flickr CC0)

Some microorganisms wait for their hosts to unintentionally deliver them a signal to multiply and kill them. After more than two years of this COVID-19 virus spreading, many people imagine a spiked ball with a mindless killer that gets into a cell and takes full control to create billions of copies of itself before attacking when they hear the word virus. Well although that’s not fully true, the “mindless killer” mentality has some truth to it.

Viruses
Courtesy of Christine Warner (Flickr CC0)

A good example to take a look at is HIV, which is the virus that causes AIDS. HIV is known as a retrovirus, it doesn’t immediately go for the kill as soon as it enters a cell. HIV waits for the perfect opportunity to command the cell to make copies and burst out to infect the other immune cells, in the meantime, it moves into your chromosomes. The final step of HIV is to cause AIDS.

Even though a virus doesn’t have the same mental capacities as we humans do, they have greatly evolved to develop some pretty elaborate decision-making skills. Research made on other viruses has shown that these pathogens can be quite thoughtful about when and what they kill. Some examples are viruses that choose to leave a cell that they have been staying in if they detect DNA damage.

Phages control bacterial populations in nature, and scientists are starting to use them to help treat bacterial infections that show no effect on antibiotics. A phage that is well studied and researched is, lambda, and it works similarly to HIV. When it enters the bacterial cell, lambda makes the decision to either replicate and kill the cell or to integrate itself into the cell’s chromosome.

But in comparison to HIV, lambda does not sit idle. Lambda uses CI, a special protein, like a stethoscope to listen for possible signs of DNA damage within the bacterial cell. If the bacterium’s phage is compromised and damaged it is bad news for the lambda. Damaged DNA is a road straight to the evolution’s landfill because it’s useless for the phage that it needs to reproduce. So, lambda replicates its genes, makes copies of itself, and then bursts out to look for damaged cells to infect.

Phages also have the power to tap the infected cell’s DNA damage sensor instead of accumulating intel with their own proteins. The protein called LexA is the infected cell’s DNA damage sensor. Transcription factors are molecules that turn genes on and off. They include proteins like CI and LexA that bind to specific genetic patterns found in chromosomes, the DNA instruction book. Coliphage 186 and other phages have found that if their chromosomes have a short DNA sequence that bacterial LexA can connect to, they don’t need to produce their own viral CI protein. LexA successfully double-crosses the cell into dying while allowing the phage to escape by causing the replicate-and-kill genes of the phage to be activated in response to DNA damage.

Coliphage 186’s counterintelligence strategy was first discovered by researchers in the late 1990s, and CI’s role in phage decision-making was discovered in the 1980s. Since then, numerous further instances of phages interfering with bacterial communication systems have been reported.

The phage phi29 is one example of this; it uses the transcription factor of its host to ascertain when the bacterium is about to create a spore or a tough bacterial egg. Phi29 instructs the cell to pack its DNA into the spore when the spore germinates, killing the growing bacterium. CtrA combines a range of internal and environmental stimuli to start a number of bacterial developmental pathways. It is essential for the growth of pili and flagella, two types of bacterial appendages. It turns out that these phages bind to the pili and flagella of bacteria to infect them.

One main theory is that phages use CtrA to predict when there will be enough pili- and flagellated bacteria in the area that they can easily infect.

These phages are not the only ones that can make complex judgments without the aid of a brain. Each time they infect a cell, some phages that attack Bacillus bacteria create a tiny chemical. The phages can detect this chemical and utilize it to determine how many phage infections are present nearby. This count assists in determining when they should activate their replicate-and-kill genes, killing only when hosts are comparatively plentiful, much like extraterrestrial invaders do. By ensuring they never run out of victims to infect, phages ensure their own long-term survival.

Why you should be interested in the counterintelligence operations carried out by bacterial viruses is a valid question. Although bacteria and people are vastly different from one another, the viruses that infect them are not that dissimilar. The exploitation of virtually every tactic employed by phages by viruses that infect people has since been demonstrated. Although having viruses listening in on your cells’ private discussions is not the best scenario, there is a bright side. Counterintelligence only functions when it is clandestine, as intelligence organizations around the world are well aware. Once discovered, the method is very readily abused to provide your adversary with false information. In a similar vein, future antiviral treatments might be able to mix traditional weapons, such as antivirals that stop viral reproduction, with information warfare ploys, including tricking the virus into thinking the cell it’s in is part of different tissue.

Written by Gabriel Salgado

Sources:

SciTechDaily: Viruses May Be “Watching” You – Lying in Wait Before Multiplying and Killing

UMBC: Viruses may be ‘watching’ you – some microbes lie in wait until their hosts unknowingly give them the signal to start multiplying and kill them

Head Topics: Viruses May Be “Watching” You – Lying in Wait Before Multiplying and Killing

Top and Featured Image Courtesy of Michael Kwok Flickr Page – Creative Commons License

Inset Image Courtesy of Christine Warner Flickr Page – Creative Commons License

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