# Bacteriophage --- **Bacteriophages** or just "phages" are [[virus|viruses]] that infect [[bacteria]] and [[archaea]]. These are the only viruses that have a [[virus#Structure|complex shape]]. They land on the outside of a bacteria and inject their genetic material directly into the cell. Bacteria are not [[bacterial immune system|entirely defenseless]] against bacteriophages, and they have their own sort of [[bacterial immune system]] with tools that specifically defend against phages. ## Replication Cycles There are two replication cycles that phages can use, **productive** or **latent/lysogenic**. - A [[productive phage infection]] creates whole, new viruses right away. Some phages can only produce productive infections and they are called "lytic" phages. - A **latent** or [[lysogenic phage infection]] is something that phages can do to store their genetic material away in the *host's* DNA, for later activation. During the "latent" period the host cell may gain new abilities. Phages that are able to produce this type of infection are called "temperate" phages. ___