A
bacteriophage (informally,
phage ) is a
virus that infects and replicates within a
bacterium. The term is derived from "bacteria" and the (
phagein), "to devour". Bacteriophages are composed of
proteins that
encapsulate a
DNA or
RNA genome, and may have relatively simple or elaborate structures. Their genomes may encode
as few as four genes, and as many as hundreds of
genes. Phages replicate within the bacterium following the injection of their genome into its
cytoplasm. Bacteriophages are among the most common and diverse entities in the
biosphere.
