Viruses have a poor reputation. They are the cause of the COVID-19 pandemic, as well as a host of other diseases that have plagued mankind since infancy. Are there any reasons to be proud of them?
Myself and many biologists believe that there is at least one type of virus, which is bacteriophages. Bacteria-infecting viruses are the ones I think about. These viruses may have instructions in their DNA that allow cells to learn new tricks.
The power of bacterial virus
Bacteriophages (or phages short) keep bacteria populations under control on both land and at sea. They can kill up to 40% of the ocean's bacteria each day and help control bacterial blooms as well as redistribution organic matter.
Doctors are also excited about their ability to selectively kill bacteria. Both engineered and natural phages can be used to treat bacterial infection that does not respond to antibiotics. This is known as phage treatment. It could be used to combat antibiotic resistance.
Recent research has revealed that phages may also play an important role in nature's genetic tinkering, creating novel genes that can be retooled by cells to gain new functions.
Phages are the most abundant form of life on Earth, and there's an estimated nonillion (a 1 with 31 zeroes) of them floating around the globe at any given moment.
Phage viruses are also known for their high mutation and replication rates. This means that they create many variants each time they reproduce.
The capsid, which is the rigid shell of most phages, contains their genetic material. The shell often has more space than what the phage requires to store its DNA.
This allows phages to store extra genetic baggage, genes that aren't necessary for their survival but that they can alter at will.
How bacteria reversed a viral switch
Let's look into the phage lifecycle to see how it plays out.
Phages are available in two main flavors: temperate or virulent. Virulent phages, like many other viruses, operate on an invade-replicate-kill program. They invade the cell and make copies of their own cells before bursting out.
Temperate phages on the other side, however, are long-term players. They can fuse their DNA with cells' DNA and remain dormant for many years before being activated. They then revert back to virulent behavior and reproduce, bursting out.
Many temperate phages use damage to DNA as their trigger. It is a signal that says "Houston, there's a problem."
If the cell's genome is being damaged, it means that the resident phage's DNA will likely be next. So the phage decides to get on board. Unless DNA damage is detected, the genes that control phage replication and burst out of cells are disabled.
Bacteria have retooled those mechanisms to create a complex genetic system that my collaborators have been studying for more than two decades.
Bacterial cells also care about whether their DNA is being damaged. If so, they activate a group of genes to try and repair their DNA. This is called the bacterial SOS response. If it fails, the cell will be destroyed.
Bacteria create the SOS response by using a protein switch-like that responds to DNA damages.
It is not surprising that phage and bacteria switches are evolutionary related. The question is: Which one invented the switch? Bacteria or viruses?
Research by us and other researchers has shown that phages were the first to reach this conclusion.
Our recent report revealed that Bacteroidetes' SOS response, which is a group of bacteria that can make up half of your gut bacteria, is controlled by a phage switch. This switch was retooled to allow the bacteria to execute its own complex genetic programs. This indicates that the bacterial SOS switch are actually phage switches that were retooled decades ago.
These phage inventions are not limited to bacterial switches.
Amazing detective work has revealed that the bacterial gene required for cell division was also created by "domestication", which is the act of inserting a phage-toxin gene.
Many bacterial attack systems, including toxins and genetic guns that are used to inject them into the cells, as well the camouflage they use in order to evade the immune defense system, have been identified or suspected to be phage-derived.
The upside to viruses
Although phages may seem cool, viruses that infect us can be quite dangerous.
There is increasing evidence that viruses infecting animals and plants are a major source for genetic innovation.
For example, it has been demonstrated that domesticated viral genes play a crucial role in the evolution and maintenance of human skin moisture.
Recent evidence suggests that even a cell's nucleus, which contains DNA, may have been an invention of the virus.
Researchers also believe that DNA may have been the first molecule to be used for life by the ancestors today's viruses. This is no small feat.
While you might think of viruses as the evil twins, they are in fact nature's most powerful source for genetic innovation. They are probably the reason that humans are here today.
Ivan Erill Associate Professor of Biology, University of Maryland Baltimore County
This article was republished by The Conversation under Creative Commons. You can read the original article.
