Bacteria, Viruses, and Protists

Virus Basics

Can a virus infect bacteria?

Yes, in particular, a bacteriophage (also called a phage) is a virus that can infect bacteria. The term “bacteriophage” means “bacteria eater” (from the Greek word phagein, meaning “to devour”). Phages consist of a long nucleic acid molecule (usually DNA) coiled within a protein head, with many of the phages having a tail attached to the head. It is the fibers extending from the tail that are often used to attach the virus to the bacterium.

Bacteriophages are classified in two ways: lytic phages destroy the host cell. When a lytic virus infects a susceptible host cell, it uses the host’s metabolic machinery to replicate viral nucleic acid and produce viral proteins. Temperate phages do not always destroy their host cell. After attachment and penetration, the DNA from a temperate phage becomes incorporated into the host bacterial DNA; it is then referred to as a prophage. The prophage replicates at the same time as the bacterial DNA—but the viral genes may be repressed indefinitely.


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