In order to infect wildly, these viruses have mastered the ability to "monitor" cells

▎Editor of WuXi AppTec content team

Viruses are often thought to be so simple in structure that they simply cannot survive without the help of cells of other organisms
.
However, these small viruses, which cannot be self-reliant, have developed a superb ability
to make full use of their environment for their own benefit.

For example, a new study published in Frontiers in Microbiology has just found that they can "monitor" the state of host cells to decide when to stay on the fly and when to replicate and break through cells in order to infect more bacteria
.

Scientists at the University of Maryland, Baltimore County (UMBC), studied bacteriophages that specifically infect a class of bacteria that grow or flagella
.

For example, the S.
s.
caulobacterales bacteria that the researchers first observed have two different forms, one form has elongated bacterial hairs or flagella, and swims freely with the help of hairs; Another form has no bacterial hairs or flagella, at this time they attach to the surface
of the object.
According to the researchers, these S.
s.
bacteria usually live in a nutrient-poor environment and are widely distributed, but when they find a good place for growth, they will change to the latter form and begin to proliferate, resulting in a large population
of cells.

The bacteriophage that infects this bacterium seems to be very good at timing, taking advantage of the opportunity of bacterial mass multiplication to rush out of the cell in order to infect as many bacteria
around it as possible.

So, how do bacteriophages grasp the timing? The researchers found that bacterial cells express a protein called CtrA, which controls when cells produce bacterial or flagella, and their protein levels fluctuate
up and down the cell cycle.
The phage genome leaves a large area that can bind to the CtrA protein, and these binding sites mean that the phage can monitor CtrA levels
within bacterial cells.

This bacteriophage virus was first found to have a binding site of CtrA, whereby the expression of CtrA in the host bacteria was monitored in order to "decide" whether to replicate in large quantities and leave the cell (image source: reference [2]; Credit：Tagide deCarvalho/UMBC）

More critically, this surveillance ability of viruses is not only the unique ability
of a certain bacteriophage.
Through detailed genomic analysis, the research team found that many different types of bacteriophages have CtrA protein binding sites, and the bacterial hosts infected by these phages also grow bacterial hairs or flagella
.
Obviously, this is not a coincidence
.

Research lead Professor Ivan Erill believes that different bacteriophages infected with different bacteria are likely to have developed the ability to monitor CtrA levels many times during evolution, and this "convergent evolution" also shows that this survival skill mastered by viruses is very effective
.
Therefore, the researchers further speculate that infections with other organisms besides viruses that infect bacteria cannot be ruled out — even human viruses have similar "surveillance" capabilities
.

"Everything we know about bacteriophages, and every evolutionary strategy they develop, has been shown to translate into viruses that infect plants and animals," Professor Erill added
.
"It's almost a matter of course
.
So if phages are monitoring their hosts, viruses that affect humans can certainly do the same
.
"For example, to optimize its survival and replication strategies, an animal virus may want to know the type of tissue it is in, or how strongly
the host responds to its infection.
"

While the virus may sound scarier, "knowing each other is invincible," the researchers note, and with these new discoveries we can develop new therapies
.
"If we're going to develop an antiviral drug and you know that the virus is monitoring a particular signal, then maybe we can manage to trick the
virus.
"