Prophages and Cryptic Prophages

Abstract

A large group of natural bacteriophages (called temperate) can establish a permanent relationship with their hosts (lysogeny), where most viral functions are repressed and the phage genome (prophage) is transmitted vertically from mother to daughters at cell division. Some prophages are inserted into the bacterial chromosome (either by site-specific recombination, like coliphage $λ$, or by transposition, like coliphage Mu-1), whereas others, like coliphage P1, establish themselves as plasmids. Established lysogens frequently suffer mutations or partial prophage deletions that destroy genes needed for lytic development. The prophage in such cases is called defective or cryptic.