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…

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…

However, like HIV, lambda is not just sitting idle. It uses a special protein called CI like a stethoscope to listen for signs of DNA damage within the bacterial cell. If the bacterium’s DNA gets compromised, that’s bad news for the lambda phage nested within it. Damaged DNA leads straight to evolution’s landfill because it’s useless for the phage that needs it to reproduce. So lambda turns on its replication genes, makes copies of itself, and bursts out of the cell to look for other undamaged cells to infect.

Scary stuff; but, interesting and perhaps even necessary information. If you’re serious about living a healthy life, there is always a need for more info about both the good guys and bad guys that live within your body.