Most of us are familiar with viruses as the tiny packets of DNA that can infect us and make us sick, and antibiotics can't help. Viruses such as smallpox, hepatitis, rabies, diphtheria, and COVID-19 are often quite deadly. But the world of viruses is much larger than those we've had bad experiences with.
Viruses infect animals, plants, funguses, and even bacteria. The viruses, or bacteriophages, that invade bacteria cells keep them at manageable levels, whether in the oceans or in our digestive systems. This is an upside to viruses that equate to "the enemy of my enemy is my friend." Scientists are experimenting with bacteriophages that can attack cancer cells. But viruses have contributed to our ecosystem in other ways.
There are two types of virus. Virulent phages are the ones that infect cells, replace their DNA, and use the cell to manufacture more virus. The other type are the temperate phages. These viruses will infect a cell and merge its DNA with that of the cell instead of evicting it. It may lie dormant and then become infectious years down the road. Or it may just create new combinations of DNA. In fact, temperate phages may be the crucial method of inserting genes that change existing life forms. Read how that happens at The Conversation. -via Damn Interesting