I HAVE ALWAYS been fascinated by viruses so I decided to specialize on plant viruses, a safer choice. Viruses are responsible for the COVID-19 pandemic and a long list of maladies that have plagued humanity since time immemorial. But is there anything good about them?

Many biologists believe there is, at least for one specific type of virus – namely, bacteriophages, or viruses that kill specific types of bacteria. Natural and engineered phages have been successfully used to treat bacterial infections that do not respond to antibiotics. This process, known as phage therapy, could help fight antibiotic resistance.

Recent research points to another important function of phages. They may be nature’s ultimate genetic tinkerers, creating novel genes that cells can retool to gain new functions.

Phages come in two main forms: temperate and virulent. Virulent phages operate on an invade-replicate-kill program. They enter the cell, hijack its components, make copies of themselves and burst out.

Temperate phages, on the other hand, play the long game. They fuse their DNA with the cell’s and may lay dormant for years until something triggers their activation. Then they revert to virulent behavior – replicate and burst out.

Virulent phages follow the lytic cycle of viral reproduction, destroying their hosts as soon as they complete replication. Temperate phages, on the other hand, follow the lysogenic cycle and stay dormant inside their host’s DNA until they’re triggered to burst out. 

Bacteria have retooled the mechanisms controlling that life cycle to generate a complex genetic system. Bacterial cells are also interested in knowing if their DNA is getting busted. If it is, they activate a set of genes that attempt to repair the DNA. This is known as the bacterial SOS response because, if it fails, the cell is killed. Bacteria orchestrate the SOS response using a switch-like protein that responds to DNA damage. It turns on if there is damage and stays off if there isn’t.

Perhaps not surprisingly, bacterial and phage switches are evolutionarily related. This prompts the question: Who invented the switch, bacteria or viruses?

Research indicates that phages got there first. It has been discovered that the SOS response of Bacteroidetes, a group of bacteria that comprise up to a half of the bacteria living in our gut, is under control of a phage switch that was retooled to implement the bacteria’s own complex genetic programs.

There is mounting evidence that the viruses that infect plants and animals are also a major source of genetic innovation in these organisms.

Recent evidence suggests that even the nucleus of a cell, which houses DNA, could have also been a viral invention. Researchers have also speculated that the ancestors of today’s viruses may have pioneered the use of DNA as the primary molecule for life.

So while many scientists may be used to thinking of viruses as the ultimate villains, they are arguably nature’s powerhouses for genetic innovation. Humans are likely here today because of them. By Manny Palomar, PhD (EV Mail June 10-16, 2024 issue)